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dawn-cmake/src/tint/resolver/uniformity.cc
Ben Clayton 23946b3606 tint: Move Switch() to own header 
castable.h is bigger than it needs to be, and pretty much every tint .cc file includes castable.h
Reduce the amount of code that .cc files that don't use Switch() need to compile.

Change-Id: Ibb4e8b0bc7104ad33a7f2f39587c7d9e749fee97
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/123401
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
2023-03-09 16:50:19 +00:00

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// Copyright 2022 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "src/tint/resolver/uniformity.h"
#include <limits>
#include <string>
#include <utility>
#include <vector>
#include "src/tint/builtin/builtin_value.h"
#include "src/tint/program_builder.h"
#include "src/tint/resolver/dependency_graph.h"
#include "src/tint/scope_stack.h"
#include "src/tint/sem/block_statement.h"
#include "src/tint/sem/builtin.h"
#include "src/tint/sem/for_loop_statement.h"
#include "src/tint/sem/function.h"
#include "src/tint/sem/if_statement.h"
#include "src/tint/sem/info.h"
#include "src/tint/sem/load.h"
#include "src/tint/sem/loop_statement.h"
#include "src/tint/sem/statement.h"
#include "src/tint/sem/switch_statement.h"
#include "src/tint/sem/value_constructor.h"
#include "src/tint/sem/value_conversion.h"
#include "src/tint/sem/variable.h"
#include "src/tint/sem/while_statement.h"
#include "src/tint/switch.h"
#include "src/tint/utils/block_allocator.h"
#include "src/tint/utils/map.h"
#include "src/tint/utils/string_stream.h"
#include "src/tint/utils/unique_vector.h"
// Set to `1` to dump the uniformity graph for each function in graphviz format.
#define TINT_DUMP_UNIFORMITY_GRAPH 0
#if TINT_DUMP_UNIFORMITY_GRAPH
#include <iostream>
#endif
namespace tint::resolver {
namespace {
/// Unwraps `u->expr`'s chain of indirect (*) and address-of (&) expressions, returning the first
/// expression that is neither of these.
/// E.g. If `u` is `*(&(*(&p)))`, returns `p`.
const ast::Expression* UnwrapIndirectAndAddressOfChain(const ast::UnaryOpExpression* u) {
auto* e = u->expr;
while (true) {
auto* unary = e->As<ast::UnaryOpExpression>();
if (unary &&
(unary->op == ast::UnaryOp::kIndirection || unary->op == ast::UnaryOp::kAddressOf)) {
e = unary->expr;
} else {
break;
}
}
return e;
}
/// CallSiteTag describes the uniformity requirements on the call sites of a function.
struct CallSiteTag {
enum {
CallSiteRequiredToBeUniform,
CallSiteNoRestriction,
} tag;
builtin::DiagnosticSeverity severity = builtin::DiagnosticSeverity::kUndefined;
};
/// FunctionTag describes a functions effects on uniformity.
enum FunctionTag {
ReturnValueMayBeNonUniform,
NoRestriction,
};
/// ParameterTag describes the uniformity requirements of values passed to a function parameter.
struct ParameterTag {
enum {
ParameterValueRequiredToBeUniform,
ParameterContentsRequiredToBeUniform,
ParameterNoRestriction,
} tag;
builtin::DiagnosticSeverity severity = builtin::DiagnosticSeverity::kUndefined;
};
/// Node represents a node in the graph of control flow and value nodes within the analysis of a
/// single function.
struct Node {
/// Constructor
/// @param a the corresponding AST node
explicit Node(const ast::Node* a) : ast(a) {}
#if TINT_DUMP_UNIFORMITY_GRAPH
/// The node tag.
std::string tag;
#endif
/// Type describes the type of the node, which is used to determine additional diagnostic
/// information.
enum Type {
kRegular,
kFunctionCallArgumentValue,
kFunctionCallArgumentContents,
kFunctionCallPointerArgumentResult,
kFunctionCallReturnValue,
};
/// The type of the node.
Type type = kRegular;
/// `true` if this node represents a potential control flow change.
bool affects_control_flow = false;
/// The corresponding AST node, or nullptr.
const ast::Node* ast = nullptr;
/// The function call argument index, if applicable.
uint32_t arg_index = 0xffffffffu;
/// The set of edges from this node to other nodes in the graph.
utils::UniqueVector<Node*, 4> edges;
/// The node that this node was visited from, or nullptr if not visited.
Node* visited_from = nullptr;
/// Add an edge to the `to` node.
/// @param to the destination node
void AddEdge(Node* to) {
TINT_ASSERT(Resolver, to != nullptr);
edges.Add(to);
}
};
/// ParameterInfo holds information about the uniformity requirements and effects for a particular
/// function parameter.
struct ParameterInfo {
/// The semantic node in corresponds to this parameter.
const sem::Parameter* sem;
/// The parameter's direct uniformity requirements.
ParameterTag tag_direct = {ParameterTag::ParameterNoRestriction};
/// The parameter's uniformity requirements that affect the function return value.
ParameterTag tag_retval = {ParameterTag::ParameterNoRestriction};
/// Will be `true` if this function may cause the contents of this pointer parameter to become
/// non-uniform.
bool pointer_may_become_non_uniform = false;
/// The parameters that are required to be uniform for the contents of this pointer parameter to
/// be uniform at function exit.
utils::Vector<const sem::Parameter*, 8> ptr_output_source_param_values;
/// The pointer parameters whose contents are required to be uniform for the contents of this
/// pointer parameter to be uniform at function exit.
utils::Vector<const sem::Parameter*, 8> ptr_output_source_param_contents;
/// The node in the graph that corresponds to this parameter's (immutable) value.
Node* value;
/// The node in the graph that corresponds to this pointer parameter's initial contents.
Node* ptr_input_contents = nullptr;
/// The node in the graph that corresponds to this pointer parameter's contents on return.
Node* ptr_output_contents = nullptr;
};
/// FunctionInfo holds information about the uniformity requirements and effects for a particular
/// function, as well as the control flow graph.
struct FunctionInfo {
/// Constructor
/// @param func the AST function
/// @param builder the program builder
FunctionInfo(const ast::Function* func, const ProgramBuilder* builder) {
name = builder->Symbols().NameFor(func->name->symbol);
callsite_tag = {CallSiteTag::CallSiteNoRestriction};
function_tag = NoRestriction;
// Create special nodes.
required_to_be_uniform_error = CreateNode({"RequiredToBeUniform_Error"});
required_to_be_uniform_warning = CreateNode({"RequiredToBeUniform_Warning"});
required_to_be_uniform_info = CreateNode({"RequiredToBeUniform_Info"});
may_be_non_uniform = CreateNode({"MayBeNonUniform"});
cf_start = CreateNode({"CF_start"});
if (func->return_type) {
value_return = CreateNode({"Value_return"});
}
// Create nodes for parameters.
parameters.Resize(func->params.Length());
for (size_t i = 0; i < func->params.Length(); i++) {
auto* param = func->params[i];
auto param_name = builder->Symbols().NameFor(param->name->symbol);
auto* sem = builder->Sem().Get<sem::Parameter>(param);
parameters[i].sem = sem;
parameters[i].value = CreateNode({"param_", param_name});
if (sem->Type()->Is<type::Pointer>()) {
// Create extra nodes for a pointer parameter's initial contents and its contents
// when the function returns.
parameters[i].ptr_input_contents =
CreateNode({"ptrparam_", param_name, "_input_contents"});
parameters[i].ptr_output_contents =
CreateNode({"ptrparam_", param_name, "_output_contents"});
variables.Set(sem, parameters[i].ptr_input_contents);
local_var_decls.Add(sem);
} else {
variables.Set(sem, parameters[i].value);
}
}
}
/// The name of the function.
std::string name;
/// The call site uniformity requirements.
CallSiteTag callsite_tag;
/// The function's uniformity effects.
FunctionTag function_tag;
/// The uniformity requirements of the function's parameters.
utils::Vector<ParameterInfo, 8> parameters;
/// The control flow graph.
utils::BlockAllocator<Node> nodes;
/// Special `RequiredToBeUniform` nodes.
Node* required_to_be_uniform_error = nullptr;
Node* required_to_be_uniform_warning = nullptr;
Node* required_to_be_uniform_info = nullptr;
/// Special `MayBeNonUniform` node.
Node* may_be_non_uniform = nullptr;
/// Special `CF_start` node.
Node* cf_start = nullptr;
/// Special `Value_return` node.
Node* value_return = nullptr;
/// Map from variables to their value nodes in the graph, scoped with respect to control flow.
ScopeStack<const sem::Variable*, Node*> variables;
/// The set of mutable variables declared in the function that are in scope at any given point
/// in the analysis. This includes the contents of parameters to the function that are pointers.
/// This is used by the analysis for if statements and loops to know which variables need extra
/// nodes to capture their state when entering/exiting those constructs.
utils::Hashset<const sem::Variable*, 8> local_var_decls;
/// The set of partial pointer variables - pointers that point to a subobject (into an array or
/// struct).
utils::Hashset<const sem::Variable*, 4> partial_ptrs;
/// LoopSwitchInfo tracks information about the value of variables for a control flow construct.
struct LoopSwitchInfo {
/// The type of this control flow construct.
std::string type;
/// The input values for local variables at the start of this construct.
utils::Hashmap<const sem::Variable*, Node*, 4> var_in_nodes;
/// The exit values for local variables at the end of this construct.
utils::Hashmap<const sem::Variable*, Node*, 4> var_exit_nodes;
};
/// @returns the RequiredToBeUniform node that corresponds to `severity`
Node* RequiredToBeUniform(builtin::DiagnosticSeverity severity) {
switch (severity) {
case builtin::DiagnosticSeverity::kError:
return required_to_be_uniform_error;
case builtin::DiagnosticSeverity::kWarning:
return required_to_be_uniform_warning;
case builtin::DiagnosticSeverity::kInfo:
return required_to_be_uniform_info;
default:
TINT_ASSERT(Resolver, false && "unhandled severity");
return nullptr;
}
}
/// @returns a LoopSwitchInfo for the given statement, allocating the LoopSwitchInfo if this is
/// the first call with the given statement.
LoopSwitchInfo& LoopSwitchInfoFor(const sem::Statement* stmt) {
return *loop_switch_infos.GetOrCreate(stmt,
[&] { return loop_switch_info_allocator.Create(); });
}
/// Disassociates the LoopSwitchInfo for the given statement.
void RemoveLoopSwitchInfoFor(const sem::Statement* stmt) { loop_switch_infos.Remove(stmt); }
/// Create a new node.
/// @param tag_list a string list that will be used to identify the node for debugging purposes
/// @param ast the optional AST node that this node corresponds to
/// @returns the new node
Node* CreateNode([[maybe_unused]] std::initializer_list<std::string_view> tag_list,
const ast::Node* ast = nullptr) {
auto* node = nodes.Create(ast);
#if TINT_DUMP_UNIFORMITY_GRAPH
// Make the tag unique and set it.
// This only matters if we're dumping the graph.
std::string tag = "";
for (auto& t : tag_list) {
tag += t;
}
std::string unique_tag = tag;
int suffix = 0;
while (tags_.Contains(unique_tag)) {
unique_tag = tag + "_$" + std::to_string(++suffix);
}
tags_.Add(unique_tag);
node->tag = name + "." + unique_tag;
#endif
return node;
}
/// Reset the visited status of every node in the graph.
void ResetVisited() {
for (auto* node : nodes.Objects()) {
node->visited_from = nullptr;
}
}
private:
/// A list of tags that have already been used within the current function.
utils::Hashset<std::string, 8> tags_;
/// Map from control flow statements to the corresponding LoopSwitchInfo structure.
utils::Hashmap<const sem::Statement*, LoopSwitchInfo*, 8> loop_switch_infos;
/// Allocator of LoopSwitchInfos
utils::BlockAllocator<LoopSwitchInfo> loop_switch_info_allocator;
};
/// UniformityGraph is used to analyze the uniformity requirements and effects of functions in a
/// module.
class UniformityGraph {
public:
/// Constructor.
/// @param builder the program to analyze
explicit UniformityGraph(ProgramBuilder* builder)
: builder_(builder), sem_(builder->Sem()), diagnostics_(builder->Diagnostics()) {}
/// Destructor.
~UniformityGraph() {}
/// Build and analyze the graph to determine whether the program satisfies the uniformity
/// constraints of WGSL.
/// @param dependency_graph the dependency-ordered module-scope declarations
/// @returns true if all uniformity constraints are satisfied, otherise false
bool Build(const DependencyGraph& dependency_graph) {
#if TINT_DUMP_UNIFORMITY_GRAPH
std::cout << "digraph G {\n";
std::cout << "rankdir=BT\n";
#endif
// Process all functions in the module.
bool success = true;
for (auto* decl : dependency_graph.ordered_globals) {
if (auto* func = decl->As<ast::Function>()) {
if (!ProcessFunction(func)) {
success = false;
break;
}
}
}
#if TINT_DUMP_UNIFORMITY_GRAPH
std::cout << "\n}\n";
#endif
return success;
}
private:
const ProgramBuilder* builder_;
const sem::Info& sem_;
diag::List& diagnostics_;
/// Map of analyzed function results.
utils::Hashmap<const ast::Function*, FunctionInfo, 8> functions_;
/// The function currently being analyzed.
FunctionInfo* current_function_;
/// Create a new node.
/// @param tag_list a string list that will be used to identify the node for debugging purposes
/// @param ast the optional AST node that this node corresponds to
/// @returns the new node
inline Node* CreateNode(std::initializer_list<std::string_view> tag_list,
const ast::Node* ast = nullptr) {
return current_function_->CreateNode(std::move(tag_list), ast);
}
/// Get the symbol name of an AST expression.
/// @param expr the expression to get the symbol name of
/// @returns the symbol name
inline std::string NameFor(const ast::IdentifierExpression* expr) {
return builder_->Symbols().NameFor(expr->identifier->symbol);
}
/// @param var the variable to get the name of
/// @returns the name of the variable @p var
inline std::string NameFor(const ast::Variable* var) {
return builder_->Symbols().NameFor(var->name->symbol);
}
/// @param var the variable to get the name of
/// @returns the name of the variable @p var
inline std::string NameFor(const sem::Variable* var) { return NameFor(var->Declaration()); }
/// @param fn the function to get the name of
/// @returns the name of the function @p fn
inline std::string NameFor(const sem::Function* fn) {
return builder_->Symbols().NameFor(fn->Declaration()->name->symbol);
}
/// Process a function.
/// @param func the function to process
/// @returns true if there are no uniformity issues, false otherwise
bool ProcessFunction(const ast::Function* func) {
current_function_ = functions_.Add(func, FunctionInfo(func, builder_)).value;
// Process function body.
if (func->body) {
ProcessStatement(current_function_->cf_start, func->body);
}
#if TINT_DUMP_UNIFORMITY_GRAPH
// Dump the graph for this function as a subgraph.
std::cout << "\nsubgraph cluster_" << current_function_->name << " {\n";
std::cout << " label=" << current_function_->name << ";";
for (auto* node : current_function_->nodes.Objects()) {
std::cout << "\n \"" << node->tag << "\";";
for (auto* edge : node->edges) {
std::cout << "\n \"" << node->tag << "\" -> \"" << edge->tag << "\";";
}
}
std::cout << "\n}\n";
#endif
/// Helper to generate a tag for the uniformity requirements of the parameter at `index`.
auto get_param_tag = [&](utils::UniqueVector<Node*, 4>& reachable, size_t index) {
auto* param = sem_.Get(func->params[index]);
auto& param_info = current_function_->parameters[index];
if (param->Type()->Is<type::Pointer>()) {
// For pointers, we distinguish between requiring uniformity of the contents versus
// the pointer itself.
if (reachable.Contains(param_info.ptr_input_contents)) {
return ParameterTag::ParameterContentsRequiredToBeUniform;
} else if (reachable.Contains(param_info.value)) {
return ParameterTag::ParameterValueRequiredToBeUniform;
}
} else if (reachable.Contains(current_function_->variables.Get(param))) {
// For non-pointers, the requirement is always on the value.
return ParameterTag::ParameterValueRequiredToBeUniform;
}
return ParameterTag::ParameterNoRestriction;
};
// Look at which nodes are reachable from "RequiredToBeUniform".
{
utils::UniqueVector<Node*, 4> reachable;
auto traverse = [&](builtin::DiagnosticSeverity severity) {
Traverse(current_function_->RequiredToBeUniform(severity), &reachable);
if (reachable.Contains(current_function_->may_be_non_uniform)) {
MakeError(*current_function_, current_function_->may_be_non_uniform, severity);
return false;
}
if (reachable.Contains(current_function_->cf_start)) {
if (current_function_->callsite_tag.tag == CallSiteTag::CallSiteNoRestriction) {
current_function_->callsite_tag = {CallSiteTag::CallSiteRequiredToBeUniform,
severity};
}
}
// Set the tags to capture the direct uniformity requirements of each parameter.
for (size_t i = 0; i < func->params.Length(); i++) {
if (current_function_->parameters[i].tag_direct.tag ==
ParameterTag::ParameterNoRestriction) {
current_function_->parameters[i].tag_direct = {get_param_tag(reachable, i),
severity};
}
}
return true;
};
if (!traverse(builtin::DiagnosticSeverity::kError)) {
return false;
} else {
if (traverse(builtin::DiagnosticSeverity::kWarning)) {
traverse(builtin::DiagnosticSeverity::kInfo);
}
}
}
// If "Value_return" exists, look at which nodes are reachable from it.
if (current_function_->value_return) {
current_function_->ResetVisited();
utils::UniqueVector<Node*, 4> reachable;
Traverse(current_function_->value_return, &reachable);
if (reachable.Contains(current_function_->may_be_non_uniform)) {
current_function_->function_tag = ReturnValueMayBeNonUniform;
}
// Set the tags to capture the uniformity requirements of each parameter with respect to
// the function return value.
for (size_t i = 0; i < func->params.Length(); i++) {
current_function_->parameters[i].tag_retval = {get_param_tag(reachable, i)};
}
}
// Traverse the graph for each pointer parameter.
for (size_t i = 0; i < func->params.Length(); i++) {
auto& param_info = current_function_->parameters[i];
if (param_info.ptr_output_contents == nullptr) {
continue;
}
// Reset "visited" state for all nodes.
current_function_->ResetVisited();
utils::UniqueVector<Node*, 4> reachable;
Traverse(param_info.ptr_output_contents, &reachable);
if (reachable.Contains(current_function_->may_be_non_uniform)) {
param_info.pointer_may_become_non_uniform = true;
}
// Check every parameter to see if it feeds into this parameter's output value.
// This includes checking this parameter (as it may feed into its own output value), so
// we do not skip the `i==j` case.
for (size_t j = 0; j < func->params.Length(); j++) {
auto tag = get_param_tag(reachable, j);
auto* source_param = sem_.Get<sem::Parameter>(func->params[j]);
if (tag == ParameterTag::ParameterContentsRequiredToBeUniform) {
param_info.ptr_output_source_param_contents.Push(source_param);
} else if (tag == ParameterTag::ParameterValueRequiredToBeUniform) {
param_info.ptr_output_source_param_values.Push(source_param);
}
}
}
return true;
}
/// Process a statement, returning the new control flow node.
/// @param cf the input control flow node
/// @param stmt the statement to process d
/// @returns the new control flow node
Node* ProcessStatement(Node* cf, const ast::Statement* stmt) {
return Switch(
stmt,
[&](const ast::AssignmentStatement* a) {
if (a->lhs->Is<ast::PhonyExpression>()) {
auto [cf_r, _] = ProcessExpression(cf, a->rhs);
return cf_r;
}
auto [cf_l, v_l, apply] = ProcessLValueExpression(cf, a->lhs);
auto [cf_r, v_r] = ProcessExpression(cf_l, a->rhs);
v_l->AddEdge(v_r);
apply();
return cf_r;
},
[&](const ast::BlockStatement* b) {
utils::Hashmap<const sem::Variable*, Node*, 4> scoped_assignments;
{
// Push a new scope for variable assignments in the block.
current_function_->variables.Push();
TINT_DEFER(current_function_->variables.Pop());
for (auto* s : b->statements) {
cf = ProcessStatement(cf, s);
if (!sem_.Get(s)->Behaviors().Contains(sem::Behavior::kNext)) {
break;
}
}
auto* parent = sem_.Get(b)->Parent();
auto* loop = parent ? parent->As<sem::LoopStatement>() : nullptr;
if (loop) {
// We've reached the end of a loop body. If there is a continuing block,
// process it before ending the block so that any variables declared in the
// loop body are visible to the continuing block.
if (auto* continuing =
loop->Declaration()->As<ast::LoopStatement>()->continuing) {
auto& loop_body_behavior = sem_.Get(b)->Behaviors();
if (loop_body_behavior.Contains(sem::Behavior::kNext) ||
loop_body_behavior.Contains(sem::Behavior::kContinue)) {
cf = ProcessStatement(cf, continuing);
}
}
}
if (sem_.Get<sem::FunctionBlockStatement>(b)) {
// We've reached the end of the function body.
// Add edges from pointer parameter outputs to their current value.
for (auto& param : current_function_->parameters) {
if (param.ptr_output_contents) {
param.ptr_output_contents->AddEdge(
current_function_->variables.Get(param.sem));
}
}
}
scoped_assignments = std::move(current_function_->variables.Top());
}
// Propagate all variables assignments to the containing scope if the behavior is
// 'Next'.
auto& behaviors = sem_.Get(b)->Behaviors();
if (behaviors.Contains(sem::Behavior::kNext)) {
for (auto var : scoped_assignments) {
current_function_->variables.Set(var.key, var.value);
}
}
// Remove any variables declared in this scope from the set of in-scope variables.
for (auto decl : sem_.Get<sem::BlockStatement>(b)->Decls()) {
current_function_->local_var_decls.Remove(decl.value.variable);
}
return cf;
},
[&](const ast::BreakStatement* b) {
// Find the loop or switch statement that we are in.
auto* parent = sem_.Get(b)
->FindFirstParent<sem::SwitchStatement, sem::LoopStatement,
sem::ForLoopStatement, sem::WhileStatement>();
auto& info = current_function_->LoopSwitchInfoFor(parent);
// Propagate variable values to the loop/switch exit nodes.
for (auto* var : current_function_->local_var_decls) {
// Skip variables that were declared inside this loop/switch.
if (auto* lv = var->As<sem::LocalVariable>();
lv &&
lv->Statement()->FindFirstParent([&](auto* s) { return s == parent; })) {
continue;
}
// Add an edge from the variable exit node to its value at this point.
auto* exit_node = info.var_exit_nodes.GetOrCreate(var, [&]() {
auto name = NameFor(var);
return CreateNode({name, "_value_", info.type, "_exit"});
});
exit_node->AddEdge(current_function_->variables.Get(var));
}
return cf;
},
[&](const ast::BreakIfStatement* b) {
// This works very similar to the IfStatement uniformity below, execpt instead of
// processing the body, we directly inline the BreakStatement uniformity from
// above.
auto [_, v_cond] = ProcessExpression(cf, b->condition);
// Add a diagnostic node to capture the control flow change.
auto* v = CreateNode({"break_if_stmt"}, b);
v->affects_control_flow = true;
v->AddEdge(v_cond);
{
auto* parent = sem_.Get(b)->FindFirstParent<sem::LoopStatement>();
auto& info = current_function_->LoopSwitchInfoFor(parent);
// Propagate variable values to the loop exit nodes.
for (auto* var : current_function_->local_var_decls) {
// Skip variables that were declared inside this loop.
if (auto* lv = var->As<sem::LocalVariable>();
lv && lv->Statement()->FindFirstParent(
[&](auto* s) { return s == parent; })) {
continue;
}
// Add an edge from the variable exit node to its value at this point.
auto* exit_node = info.var_exit_nodes.GetOrCreate(var, [&]() {
auto name = NameFor(var);
return CreateNode({name, "_value_", info.type, "_exit"});
});
exit_node->AddEdge(current_function_->variables.Get(var));
}
}
auto* sem_break_if = sem_.Get(b);
if (sem_break_if->Behaviors() != sem::Behaviors{sem::Behavior::kNext}) {
auto* cf_end = CreateNode({"break_if_CFend"});
cf_end->AddEdge(v);
return cf_end;
}
return cf;
},
[&](const ast::CallStatement* c) {
auto [cf1, _] = ProcessCall(cf, c->expr);
return cf1;
},
[&](const ast::CompoundAssignmentStatement* c) {
// The compound assignment statement `a += b` is equivalent to:
// let p = &a;
// *p = *p + b;
// Note: we set load_rule=true when evaluating the LHS, as the resolver does not add
// a load node for it.
auto [cf1, l1, apply] = ProcessLValueExpression(cf, c->lhs);
auto [cf2, v2] = ProcessExpression(cf1, c->lhs, /* load_rule */ true);
auto [cf3, v3] = ProcessExpression(cf2, c->rhs);
auto* result = CreateNode({"binary_expr_result"});
result->AddEdge(v2);
result->AddEdge(v3);
l1->AddEdge(result);
apply();
return cf3;
},
[&](const ast::ContinueStatement* c) {
// Find the loop statement that we are in.
auto* parent = sem_.Get(c)
->FindFirstParent<sem::LoopStatement, sem::ForLoopStatement,
sem::WhileStatement>();
auto& info = current_function_->LoopSwitchInfoFor(parent);
// Propagate assignments to the loop input nodes.
for (auto v : info.var_in_nodes) {
auto* in_node = v.value;
auto* out_node = current_function_->variables.Get(v.key);
if (out_node != in_node) {
in_node->AddEdge(out_node);
}
}
return cf;
},
[&](const ast::DiscardStatement*) { return cf; },
[&](const ast::ForLoopStatement* f) {
auto* sem_loop = sem_.Get(f);
auto* cfx = CreateNode({"loop_start"});
// Insert the initializer before the loop.
auto* cf_init = cf;
if (f->initializer) {
cf_init = ProcessStatement(cf, f->initializer);
}
auto* cf_start = cf_init;
auto& info = current_function_->LoopSwitchInfoFor(sem_loop);
info.type = "forloop";
// Create input nodes for any variables declared before this loop.
for (auto* v : current_function_->local_var_decls) {
auto* in_node = CreateNode({NameFor(v), "_value_forloop_in"});
in_node->AddEdge(current_function_->variables.Get(v));
info.var_in_nodes.Replace(v, in_node);
current_function_->variables.Set(v, in_node);
}
// Insert the condition at the start of the loop body.
if (f->condition) {
auto [cf_cond, v] = ProcessExpression(cfx, f->condition);
auto* cf_condition_end = CreateNode({"for_condition_CFend"}, f);
cf_condition_end->affects_control_flow = true;
cf_condition_end->AddEdge(v);
cf_start = cf_condition_end;
// Propagate assignments to the loop exit nodes.
for (auto* var : current_function_->local_var_decls) {
auto* exit_node = info.var_exit_nodes.GetOrCreate(var, [&]() {
auto name = NameFor(var);
return CreateNode({name, "_value_", info.type, "_exit"});
});
exit_node->AddEdge(current_function_->variables.Get(var));
}
}
auto* cf1 = ProcessStatement(cf_start, f->body);
// Insert the continuing statement at the end of the loop body.
if (f->continuing) {
auto* cf2 = ProcessStatement(cf1, f->continuing);
cfx->AddEdge(cf2);
} else {
cfx->AddEdge(cf1);
}
cfx->AddEdge(cf);
// Add edges from variable loop input nodes to their values at the end of the loop.
for (auto v : info.var_in_nodes) {
auto* in_node = v.value;
auto* out_node = current_function_->variables.Get(v.key);
if (out_node != in_node) {
in_node->AddEdge(out_node);
}
}
// Set each variable's exit node as its value in the outer scope.
for (auto v : info.var_exit_nodes) {
current_function_->variables.Set(v.key, v.value);
}
if (f->initializer) {
// Remove variables declared in the for-loop initializer from the current scope.
if (auto* decl = f->initializer->As<ast::VariableDeclStatement>()) {
current_function_->local_var_decls.Remove(sem_.Get(decl->variable));
}
}
current_function_->RemoveLoopSwitchInfoFor(sem_loop);
if (sem_loop->Behaviors() == sem::Behaviors{sem::Behavior::kNext}) {
return cf;
} else {
return cfx;
}
},
[&](const ast::WhileStatement* w) {
auto* sem_loop = sem_.Get(w);
auto* cfx = CreateNode({"loop_start"});
auto* cf_start = cf;
auto& info = current_function_->LoopSwitchInfoFor(sem_loop);
info.type = "whileloop";
// Create input nodes for any variables declared before this loop.
for (auto* v : current_function_->local_var_decls) {
auto* in_node = CreateNode({NameFor(v), "_value_forloop_in"});
in_node->AddEdge(current_function_->variables.Get(v));
info.var_in_nodes.Replace(v, in_node);
current_function_->variables.Set(v, in_node);
}
// Insert the condition at the start of the loop body.
{
auto [cf_cond, v] = ProcessExpression(cfx, w->condition);
auto* cf_condition_end = CreateNode({"while_condition_CFend"}, w);
cf_condition_end->affects_control_flow = true;
cf_condition_end->AddEdge(v);
cf_start = cf_condition_end;
}
// Propagate assignments to the loop exit nodes.
for (auto* var : current_function_->local_var_decls) {
auto* exit_node = info.var_exit_nodes.GetOrCreate(var, [&]() {
auto name = NameFor(var);
return CreateNode({name, "_value_", info.type, "_exit"});
});
exit_node->AddEdge(current_function_->variables.Get(var));
}
auto* cf1 = ProcessStatement(cf_start, w->body);
cfx->AddEdge(cf1);
cfx->AddEdge(cf);
// Add edges from variable loop input nodes to their values at the end of the loop.
for (auto v : info.var_in_nodes) {
auto* in_node = v.value;
auto* out_node = current_function_->variables.Get(v.key);
if (out_node != in_node) {
in_node->AddEdge(out_node);
}
}
// Set each variable's exit node as its value in the outer scope.
for (auto v : info.var_exit_nodes) {
current_function_->variables.Set(v.key, v.value);
}
current_function_->RemoveLoopSwitchInfoFor(sem_loop);
if (sem_loop->Behaviors() == sem::Behaviors{sem::Behavior::kNext}) {
return cf;
} else {
return cfx;
}
},
[&](const ast::IfStatement* i) {
auto* sem_if = sem_.Get(i);
auto [_, v_cond] = ProcessExpression(cf, i->condition);
// Add a diagnostic node to capture the control flow change.
auto* v = CreateNode({"if_stmt"}, i);
v->affects_control_flow = true;
v->AddEdge(v_cond);
utils::Hashmap<const sem::Variable*, Node*, 4> true_vars;
utils::Hashmap<const sem::Variable*, Node*, 4> false_vars;
// Helper to process a statement with a new scope for variable assignments.
// Populates `assigned_vars` with new nodes for any variables that are assigned in
// this statement.
auto process_in_scope =
[&](Node* cf_in, const ast::Statement* s,
utils::Hashmap<const sem::Variable*, Node*, 4>& assigned_vars) {
// Push a new scope for variable assignments.
current_function_->variables.Push();
// Process the statement.
auto* cf_out = ProcessStatement(cf_in, s);
assigned_vars = current_function_->variables.Top();
// Pop the scope and return.
current_function_->variables.Pop();
return cf_out;
};
auto* cf1 = process_in_scope(v, i->body, true_vars);
bool true_has_next = sem_.Get(i->body)->Behaviors().Contains(sem::Behavior::kNext);
bool false_has_next = true;
Node* cf2 = nullptr;
if (i->else_statement) {
cf2 = process_in_scope(v, i->else_statement, false_vars);
false_has_next =
sem_.Get(i->else_statement)->Behaviors().Contains(sem::Behavior::kNext);
}
// Update values for any variables assigned in the if or else blocks.
for (auto* var : current_function_->local_var_decls) {
// Skip variables not assigned in either block.
if (!true_vars.Contains(var) && !false_vars.Contains(var)) {
continue;
}
// Create an exit node for the variable.
auto* out_node = CreateNode({NameFor(var), "_value_if_exit"});
// Add edges to the assigned value or the initial value.
// Only add edges if the behavior for that block contains 'Next'.
if (true_has_next) {
if (true_vars.Contains(var)) {
out_node->AddEdge(*true_vars.Find(var));
} else {
out_node->AddEdge(current_function_->variables.Get(var));
}
}
if (false_has_next) {
if (false_vars.Contains(var)) {
out_node->AddEdge(*false_vars.Find(var));
} else {
out_node->AddEdge(current_function_->variables.Get(var));
}
}
current_function_->variables.Set(var, out_node);
}
if (sem_if->Behaviors() != sem::Behaviors{sem::Behavior::kNext}) {
auto* cf_end = CreateNode({"if_CFend"});
cf_end->AddEdge(cf1);
if (cf2) {
cf_end->AddEdge(cf2);
}
return cf_end;
}
return cf;
},
[&](const ast::IncrementDecrementStatement* i) {
// The increment/decrement statement `i++` is equivalent to `i = i + 1`.
// Note: we set load_rule=true when evaluating the LHS the first time, as the
// resolver does not add a load node for it.
auto [cf1, v1] = ProcessExpression(cf, i->lhs, /* load_rule */ true);
auto* result = CreateNode({"incdec_result"});
result->AddEdge(v1);
result->AddEdge(cf1);
auto [cf2, l2, apply] = ProcessLValueExpression(cf1, i->lhs);
l2->AddEdge(result);
apply();
return cf2;
},
[&](const ast::LoopStatement* l) {
auto* sem_loop = sem_.Get(l);
auto* cfx = CreateNode({"loop_start"});
auto& info = current_function_->LoopSwitchInfoFor(sem_loop);
info.type = "loop";
// Create input nodes for any variables declared before this loop.
for (auto* v : current_function_->local_var_decls) {
auto name = NameFor(v);
auto* in_node = CreateNode({name, "_value_loop_in"}, v->Declaration());
in_node->AddEdge(current_function_->variables.Get(v));
info.var_in_nodes.Replace(v, in_node);
current_function_->variables.Set(v, in_node);
}
// Note: The continuing block is processed as a special case at the end of
// processing the loop body BlockStatement. This is so that variable declarations
// inside the loop body are visible to the continuing statement.
auto* cf1 = ProcessStatement(cfx, l->body);
cfx->AddEdge(cf1);
cfx->AddEdge(cf);
// Add edges from variable loop input nodes to their values at the end of the loop.
for (auto v : info.var_in_nodes) {
auto* in_node = v.value;
auto* out_node = current_function_->variables.Get(v.key);
if (out_node != in_node) {
in_node->AddEdge(out_node);
}
}
// Set each variable's exit node as its value in the outer scope.
for (auto v : info.var_exit_nodes) {
current_function_->variables.Set(v.key, v.value);
}
current_function_->RemoveLoopSwitchInfoFor(sem_loop);
if (sem_loop->Behaviors() == sem::Behaviors{sem::Behavior::kNext}) {
return cf;
} else {
return cfx;
}
},
[&](const ast::ReturnStatement* r) {
Node* cf_ret;
if (r->value) {
auto [cf1, v] = ProcessExpression(cf, r->value);
current_function_->value_return->AddEdge(v);
cf_ret = cf1;
} else {
TINT_ASSERT(Resolver, cf != nullptr);
cf_ret = cf;
}
// Add edges from each pointer parameter output to its current value.
for (auto& param : current_function_->parameters) {
if (param.ptr_output_contents) {
param.ptr_output_contents->AddEdge(
current_function_->variables.Get(param.sem));
}
}
return cf_ret;
},
[&](const ast::SwitchStatement* s) {
auto* sem_switch = sem_.Get(s);
auto [cfx, v_cond] = ProcessExpression(cf, s->condition);
// Add a diagnostic node to capture the control flow change.
auto* v = CreateNode({"switch_stmt"}, s);
v->affects_control_flow = true;
v->AddEdge(v_cond);
Node* cf_end = nullptr;
if (sem_switch->Behaviors() != sem::Behaviors{sem::Behavior::kNext}) {
cf_end = CreateNode({"switch_CFend"});
}
auto& info = current_function_->LoopSwitchInfoFor(sem_switch);
info.type = "switch";
auto* cf_n = v;
for (auto* c : s->body) {
auto* sem_case = sem_.Get(c);
current_function_->variables.Push();
cf_n = ProcessStatement(v, c->body);
if (cf_end) {
cf_end->AddEdge(cf_n);
}
if (sem_case->Behaviors().Contains(sem::Behavior::kNext)) {
// Propagate variable values to the switch exit nodes.
for (auto* var : current_function_->local_var_decls) {
// Skip variables that were declared inside the switch.
if (auto* lv = var->As<sem::LocalVariable>();
lv && lv->Statement()->FindFirstParent(
[&](auto* st) { return st == sem_switch; })) {
continue;
}
// Add an edge from the variable exit node to its new value.
auto* exit_node = info.var_exit_nodes.GetOrCreate(var, [&]() {
auto name = NameFor(var);
return CreateNode({name, "_value_", info.type, "_exit"});
});
exit_node->AddEdge(current_function_->variables.Get(var));
}
}
current_function_->variables.Pop();
}
// Update nodes for any variables assigned in the switch statement.
for (auto var : info.var_exit_nodes) {
current_function_->variables.Set(var.key, var.value);
}
return cf_end ? cf_end : cf;
},
[&](const ast::VariableDeclStatement* decl) {
Node* node;
auto* sem_var = sem_.Get(decl->variable);
if (decl->variable->initializer) {
auto [cf1, v] = ProcessExpression(cf, decl->variable->initializer);
cf = cf1;
node = v;
// Store if lhs is a partial pointer
if (sem_var->Type()->Is<type::Pointer>()) {
auto* init = sem_.Get(decl->variable->initializer);
if (auto* unary_init = init->Declaration()->As<ast::UnaryOpExpression>()) {
auto* e = UnwrapIndirectAndAddressOfChain(unary_init);
if (e->Is<ast::AccessorExpression>()) {
current_function_->partial_ptrs.Add(sem_var);
}
}
}
} else {
node = cf;
}
current_function_->variables.Set(sem_var, node);
if (decl->variable->Is<ast::Var>()) {
current_function_->local_var_decls.Add(
sem_.Get<sem::LocalVariable>(decl->variable));
}
return cf;
},
[&](const ast::ConstAssert*) {
return cf; // No impact on uniformity
},
[&](Default) {
TINT_ICE(Resolver, diagnostics_)
<< "unknown statement type: " << std::string(stmt->TypeInfo().name);
return nullptr;
});
}
/// Process an identifier expression.
/// @param cf the input control flow node
/// @param ident the identifier expression to process
/// @param load_rule true if the load rule is being invoked on this identifier
/// @returns a pair of (control flow node, value node)
std::pair<Node*, Node*> ProcessIdentExpression(Node* cf,
const ast::IdentifierExpression* ident,
bool load_rule = false) {
// Helper to check if the entry point attribute of `obj` indicates non-uniformity.
auto has_nonuniform_entry_point_attribute = [&](auto* obj) {
// Only the num_workgroups and workgroup_id builtins are uniform.
if (auto* builtin_attr = ast::GetAttribute<ast::BuiltinAttribute>(obj->attributes)) {
auto builtin = builder_->Sem().Get(builtin_attr)->Value();
if (builtin == builtin::BuiltinValue::kNumWorkgroups ||
builtin == builtin::BuiltinValue::kWorkgroupId) {
return false;
}
}
return true;
};
auto* node = CreateNode({NameFor(ident), "_ident_expr"}, ident);
auto* sem_ident = sem_.GetVal(ident);
TINT_ASSERT(Resolver, sem_ident);
auto* var_user = sem_ident->Unwrap()->As<sem::VariableUser>();
auto* sem = var_user->Variable();
return Switch(
sem,
[&](const sem::Parameter* param) {
auto* user_func = param->Owner()->As<sem::Function>();
if (user_func && user_func->Declaration()->IsEntryPoint()) {
if (auto* str = param->Type()->As<sem::Struct>()) {
// We consider the whole struct to be non-uniform if any one of its members
// is non-uniform.
bool uniform = true;
for (auto* member : str->Members()) {
if (has_nonuniform_entry_point_attribute(member->Declaration())) {
uniform = false;
}
}
node->AddEdge(uniform ? cf : current_function_->may_be_non_uniform);
return std::make_pair(cf, node);
} else {
if (has_nonuniform_entry_point_attribute(param->Declaration())) {
node->AddEdge(current_function_->may_be_non_uniform);
} else {
node->AddEdge(cf);
}
return std::make_pair(cf, node);
}
} else {
node->AddEdge(cf);
auto* current_value = current_function_->variables.Get(param);
if (param->Type()->Is<type::Pointer>()) {
if (load_rule) {
// We are loading from the pointer, so add an edge to its contents.
node->AddEdge(current_value);
} else {
// This is a pointer parameter that we are not loading from, so add an
// edge to the pointer value itself.
node->AddEdge(current_function_->parameters[param->Index()].value);
}
} else {
// The parameter is a value, so add an edge to it.
node->AddEdge(current_value);
}
return std::make_pair(cf, node);
}
},
[&](const sem::GlobalVariable* global) {
// Loads from global read-write variables may be non-uniform.
if (global->Declaration()->Is<ast::Var>() &&
global->Access() != builtin::Access::kRead && load_rule) {
node->AddEdge(current_function_->may_be_non_uniform);
} else {
node->AddEdge(cf);
}
return std::make_pair(cf, node);
},
[&](const sem::LocalVariable* local) {
node->AddEdge(cf);
auto* local_value = current_function_->variables.Get(local);
if (local->Type()->Is<type::Pointer>()) {
if (load_rule) {
// We are loading from the pointer, so add an edge to its contents.
auto* root = var_user->RootIdentifier();
if (root->Is<sem::GlobalVariable>()) {
if (root->Access() != builtin::Access::kRead) {
// The contents of a mutable global variable is always non-uniform.
node->AddEdge(current_function_->may_be_non_uniform);
}
} else {
node->AddEdge(current_function_->variables.Get(root));
}
// The uniformity of the contents also depends on the uniformity of the
// pointer itself. For a pointer captured in a let declaration, this will
// come from the value node of that declaration.
node->AddEdge(local_value);
} else {
// The variable is a pointer that we are not loading from, so add an edge to
// the pointer value itself.
node->AddEdge(local_value);
}
} else if (local->Type()->Is<type::Reference>()) {
if (load_rule) {
// We are loading from the reference, so add an edge to its contents.
node->AddEdge(local_value);
} else {
// References to local variables (i.e. var declarations) are always uniform,
// so no other edges needed.
}
} else {
// The identifier is a value declaration, so add an edge to it.
node->AddEdge(local_value);
}
return std::make_pair(cf, node);
},
[&](Default) {
TINT_ICE(Resolver, diagnostics_)
<< "unknown identifier expression type: " << std::string(sem->TypeInfo().name);
return std::pair<Node*, Node*>(nullptr, nullptr);
});
}
/// Process an expression.
/// @param cf the input control flow node
/// @param expr the expression to process
/// @param load_rule true if the load rule is being invoked on this expression
/// @returns a pair of (control flow node, value node)
std::pair<Node*, Node*> ProcessExpression(Node* cf,
const ast::Expression* expr,
bool load_rule = false) {
if (sem_.Get<sem::Load>(expr)) {
// Set the load-rule flag to indicate that identifier expressions in this sub-tree
// should add edges to the contents of the variables that they refer to.
load_rule = true;
}
return Switch(
expr,
[&](const ast::BinaryExpression* b) {
if (b->IsLogical()) {
// Short-circuiting binary operators are a special case.
auto [cf1, v1] = ProcessExpression(cf, b->lhs);
// Add a diagnostic node to capture the control flow change.
auto* v1_cf = CreateNode({"short_circuit_op"}, b);
v1_cf->affects_control_flow = true;
v1_cf->AddEdge(v1);
auto [cf2, v2] = ProcessExpression(v1_cf, b->rhs);
return std::pair<Node*, Node*>(cf, v2);
} else {
auto [cf1, v1] = ProcessExpression(cf, b->lhs);
auto [cf2, v2] = ProcessExpression(cf1, b->rhs);
auto* result = CreateNode({"binary_expr_result"}, b);
result->AddEdge(v1);
result->AddEdge(v2);
return std::pair<Node*, Node*>(cf2, result);
}
},
[&](const ast::BitcastExpression* b) { return ProcessExpression(cf, b->expr); },
[&](const ast::CallExpression* c) { return ProcessCall(cf, c); },
[&](const ast::IdentifierExpression* i) {
return ProcessIdentExpression(cf, i, load_rule);
},
[&](const ast::IndexAccessorExpression* i) {
auto [cf1, v1] = ProcessExpression(cf, i->object, load_rule);
auto [cf2, v2] = ProcessExpression(cf1, i->index);
auto* result = CreateNode({"index_accessor_result"});
result->AddEdge(v1);
result->AddEdge(v2);
return std::pair<Node*, Node*>(cf2, result);
},
[&](const ast::LiteralExpression*) { return std::make_pair(cf, cf); },
[&](const ast::MemberAccessorExpression* m) {
return ProcessExpression(cf, m->object, load_rule);
},
[&](const ast::UnaryOpExpression* u) {
return ProcessExpression(cf, u->expr, load_rule);
},
[&](Default) {
TINT_ICE(Resolver, diagnostics_)
<< "unknown expression type: " << std::string(expr->TypeInfo().name);
return std::pair<Node*, Node*>(nullptr, nullptr);
});
}
/// @param u unary expression with op == kIndirection
/// @returns true if `u` is an indirection unary expression that ultimately dereferences a
/// partial pointer, false otherwise.
bool IsDerefOfPartialPointer(const ast::UnaryOpExpression* u) {
TINT_ASSERT(Resolver, u->op == ast::UnaryOp::kIndirection);
// To determine if we're dereferencing a partial pointer, unwrap *&
// chains; if the final expression is an identifier, see if it's a
// partial pointer. If it's not an identifier, then it must be an
// index/member accessor expression, and thus a partial pointer.
auto* e = UnwrapIndirectAndAddressOfChain(u);
if (auto* var_user = sem_.Get<sem::VariableUser>(e)) {
if (current_function_->partial_ptrs.Contains(var_user->Variable())) {
return true;
}
} else {
TINT_ASSERT(Resolver, e->Is<ast::AccessorExpression>());
return true;
}
return false;
}
/// LValue holds the Nodes returned by ProcessLValueExpression()
struct LValue {
/// The control-flow node for an LValue expression
Node* cf = nullptr;
/// The new value node for an LValue expression
Node* new_val = nullptr;
/// Updates the value node of the LValue expression to be #new_val.
std::function<void()> apply;
};
/// Process an LValue expression.
/// @param cf the input control flow node
/// @param expr the expression to process
/// @returns a pair of (control flow node, variable node)
LValue ProcessLValueExpression(Node* cf,
const ast::Expression* expr,
bool is_partial_reference = false) {
return Switch(
expr,
[&](const ast::IdentifierExpression* i) {
auto* sem = sem_.GetVal(i)->UnwrapLoad()->As<sem::VariableUser>();
if (sem->Variable()->Is<sem::GlobalVariable>()) {
return LValue{cf, current_function_->may_be_non_uniform, [] {}};
} else if (auto* local = sem->Variable()->As<sem::LocalVariable>()) {
// Create a new value node for this variable.
auto* value = CreateNode({NameFor(i), "_lvalue"});
auto apply = [=] { current_function_->variables.Set(local, value); };
// If i is part of an expression that is a partial reference to a variable (e.g.
// index or member access), we link back to the variable's previous value. If
// the previous value was non-uniform, a partial assignment will not make it
// uniform.
auto* old_value = current_function_->variables.Get(local);
if (is_partial_reference && old_value) {
value->AddEdge(old_value);
}
return LValue{cf, value, apply};
} else {
TINT_ICE(Resolver, diagnostics_)
<< "unknown lvalue identifier expression type: "
<< std::string(sem->Variable()->TypeInfo().name);
return LValue{};
}
},
[&](const ast::IndexAccessorExpression* i) {
auto [cf1, l1, apply] =
ProcessLValueExpression(cf, i->object, /*is_partial_reference*/ true);
auto [cf2, v2] = ProcessExpression(cf1, i->index);
l1->AddEdge(v2);
return LValue{cf2, l1, apply};
},
[&](const ast::MemberAccessorExpression* m) {
return ProcessLValueExpression(cf, m->object, /*is_partial_reference*/ true);
},
[&](const ast::UnaryOpExpression* u) {
if (u->op == ast::UnaryOp::kIndirection) {
// Cut the analysis short, since we only need to know the originating variable
// that is being written to.
auto* root_ident = sem_.Get(u)->RootIdentifier();
auto* deref = CreateNode({NameFor(root_ident), "_deref"});
auto apply = [=] { current_function_->variables.Set(root_ident, deref); };
if (auto* old_value = current_function_->variables.Get(root_ident)) {
// If dereferencing a partial reference or partial pointer, we link back to
// the variable's previous value. If the previous value was non-uniform, a
// partial assignment will not make it uniform.
if (is_partial_reference || IsDerefOfPartialPointer(u)) {
deref->AddEdge(old_value);
}
}
return LValue{cf, deref, apply};
}
return ProcessLValueExpression(cf, u->expr, is_partial_reference);
},
[&](Default) {
TINT_ICE(Resolver, diagnostics_)
<< "unknown lvalue expression type: " << std::string(expr->TypeInfo().name);
return LValue{};
});
}
/// Process a function call expression.
/// @param cf the input control flow node
/// @param call the function call to process
/// @returns a pair of (control flow node, value node)
std::pair<Node*, Node*> ProcessCall(Node* cf, const ast::CallExpression* call) {
std::string name = NameFor(call->target);
// Process call arguments
Node* cf_last_arg = cf;
utils::Vector<Node*, 8> args;
utils::Vector<Node*, 8> ptrarg_contents;
ptrarg_contents.Resize(call->args.Length());
for (size_t i = 0; i < call->args.Length(); i++) {
auto [cf_i, arg_i] = ProcessExpression(cf_last_arg, call->args[i]);
// Capture the index of this argument in a new node.
// Note: This is an additional node that isn't described in the specification, for the
// purpose of providing diagnostic information.
Node* arg_node = CreateNode({name, "_arg_", std::to_string(i)}, call);
arg_node->type = Node::kFunctionCallArgumentValue;
arg_node->arg_index = static_cast<uint32_t>(i);
arg_node->AddEdge(arg_i);
// For pointer arguments, create an additional node to represent the contents of that
// pointer prior to the function call.
auto* sem_arg = sem_.GetVal(call->args[i]);
if (sem_arg->Type()->Is<type::Pointer>()) {
auto* arg_contents =
CreateNode({name, "_ptrarg_", std::to_string(i), "_contents"}, call);
arg_contents->type = Node::kFunctionCallArgumentContents;
arg_contents->arg_index = static_cast<uint32_t>(i);
auto* root = sem_arg->RootIdentifier();
if (root->Is<sem::GlobalVariable>()) {
if (root->Access() != builtin::Access::kRead) {
// The contents of a mutable global variable is always non-uniform.
arg_contents->AddEdge(current_function_->may_be_non_uniform);
}
} else {
arg_contents->AddEdge(current_function_->variables.Get(root));
}
arg_contents->AddEdge(arg_node);
ptrarg_contents[i] = arg_contents;
}
cf_last_arg = cf_i;
args.Push(arg_node);
}
// Note: This is an additional node that isn't described in the specification, for the
// purpose of providing diagnostic information.
Node* call_node = CreateNode({name, "_call"}, call);
call_node->AddEdge(cf_last_arg);
Node* result = CreateNode({name, "_return_value"}, call);
result->type = Node::kFunctionCallReturnValue;
Node* cf_after = CreateNode({"CF_after_", name}, call);
auto default_severity = kUniformityFailuresAsError ? builtin::DiagnosticSeverity::kError
: builtin::DiagnosticSeverity::kWarning;
// Get tags for the callee.
CallSiteTag callsite_tag = {CallSiteTag::CallSiteNoRestriction};
FunctionTag function_tag = NoRestriction;
auto* sem = SemCall(call);
const FunctionInfo* func_info = nullptr;
Switch(
sem->Target(),
[&](const sem::Builtin* builtin) {
// Most builtins have no restrictions. The exceptions are barriers, derivatives,
// some texture sampling builtins, and atomics.
if (builtin->IsBarrier()) {
callsite_tag = {CallSiteTag::CallSiteRequiredToBeUniform, default_severity};
} else if (builtin->Type() == builtin::Function::kWorkgroupUniformLoad) {
callsite_tag = {CallSiteTag::CallSiteRequiredToBeUniform, default_severity};
} else if (builtin->IsDerivative() ||
builtin->Type() == builtin::Function::kTextureSample ||
builtin->Type() == builtin::Function::kTextureSampleBias ||
builtin->Type() == builtin::Function::kTextureSampleCompare) {
// Get the severity of derivative uniformity violations in this context.
auto severity = sem_.DiagnosticSeverity(
call, builtin::DiagnosticRule::kDerivativeUniformity);
if (severity != builtin::DiagnosticSeverity::kOff) {
callsite_tag = {CallSiteTag::CallSiteRequiredToBeUniform, severity};
}
function_tag = ReturnValueMayBeNonUniform;
} else if (builtin->IsAtomic()) {
callsite_tag = {CallSiteTag::CallSiteNoRestriction};
function_tag = ReturnValueMayBeNonUniform;
}
},
[&](const sem::Function* func) {
// We must have already analyzed the user-defined function since we process
// functions in dependency order.
auto info = functions_.Find(func->Declaration());
TINT_ASSERT(Resolver, info != nullptr);
callsite_tag = info->callsite_tag;
function_tag = info->function_tag;
func_info = info;
},
[&](const sem::ValueConstructor*) {
callsite_tag = {CallSiteTag::CallSiteNoRestriction};
function_tag = NoRestriction;
},
[&](const sem::ValueConversion*) {
callsite_tag = {CallSiteTag::CallSiteNoRestriction};
function_tag = NoRestriction;
},
[&](Default) {
TINT_ICE(Resolver, diagnostics_) << "unhandled function call target: " << name;
});
cf_after->AddEdge(call_node);
if (function_tag == ReturnValueMayBeNonUniform) {
result->AddEdge(current_function_->may_be_non_uniform);
}
result->AddEdge(cf_after);
// For each argument, add edges based on parameter tags.
for (size_t i = 0; i < args.Length(); i++) {
if (func_info) {
auto& param_info = func_info->parameters[i];
// Capture the direct uniformity requirements.
switch (param_info.tag_direct.tag) {
case ParameterTag::ParameterValueRequiredToBeUniform:
current_function_->RequiredToBeUniform(param_info.tag_direct.severity)
->AddEdge(args[i]);
break;
case ParameterTag::ParameterContentsRequiredToBeUniform: {
current_function_->RequiredToBeUniform(param_info.tag_direct.severity)
->AddEdge(ptrarg_contents[i]);
break;
}
case ParameterTag::ParameterNoRestriction:
break;
}
// Capture the effects of this parameter on the return value.
switch (param_info.tag_retval.tag) {
case ParameterTag::ParameterValueRequiredToBeUniform:
result->AddEdge(args[i]);
break;
case ParameterTag::ParameterContentsRequiredToBeUniform: {
result->AddEdge(ptrarg_contents[i]);
break;
}
case ParameterTag::ParameterNoRestriction:
break;
}
// Capture the effects of other call parameters on the contents of this parameter
// after the call returns.
auto* sem_arg = sem_.GetVal(call->args[i]);
if (sem_arg->Type()->Is<type::Pointer>()) {
auto* ptr_result =
CreateNode({name, "_ptrarg_", std::to_string(i), "_result"}, call);
ptr_result->type = Node::kFunctionCallPointerArgumentResult;
ptr_result->arg_index = static_cast<uint32_t>(i);
if (param_info.pointer_may_become_non_uniform) {
ptr_result->AddEdge(current_function_->may_be_non_uniform);
} else {
// Add edge to the call to catch when it's called in non-uniform control
// flow.
ptr_result->AddEdge(call_node);
// Add edges from the resulting pointer value to any other arguments that
// feed it. We distinguish between requirements on the source arguments
// value versus its contents for pointer arguments.
for (auto* source : param_info.ptr_output_source_param_values) {
ptr_result->AddEdge(args[source->Index()]);
}
for (auto* source : param_info.ptr_output_source_param_contents) {
ptr_result->AddEdge(ptrarg_contents[source->Index()]);
}
}
// Update the current stored value for this pointer argument.
auto* root_ident = sem_arg->RootIdentifier();
TINT_ASSERT(Resolver, root_ident);
current_function_->variables.Set(root_ident, ptr_result);
}
} else {
auto* builtin = sem->Target()->As<sem::Builtin>();
if (builtin && builtin->Type() == builtin::Function::kWorkgroupUniformLoad) {
// The workgroupUniformLoad builtin requires its parameter to be uniform.
current_function_->RequiredToBeUniform(default_severity)->AddEdge(args[i]);
} else {
// All other builtin function parameters are RequiredToBeUniformForReturnValue,
// as are parameters for value constructors and value conversions.
result->AddEdge(args[i]);
}
}
}
// Add the callsite requirement last.
// We traverse edges in reverse order, so this makes the callsite requirement take highest
// priority when reporting violations.
if (callsite_tag.tag == CallSiteTag::CallSiteRequiredToBeUniform) {
current_function_->RequiredToBeUniform(callsite_tag.severity)->AddEdge(call_node);
}
return {cf_after, result};
}
/// Traverse a graph starting at `source`, inserting all visited nodes into `reachable` and
/// recording which node they were reached from.
/// @param source the starting node
/// @param reachable the set of reachable nodes to populate, if required
void Traverse(Node* source, utils::UniqueVector<Node*, 4>* reachable = nullptr) {
utils::Vector<Node*, 8> to_visit{source};
while (!to_visit.IsEmpty()) {
auto* node = to_visit.Back();
to_visit.Pop();
if (reachable) {
reachable->Add(node);
}
for (auto* to : node->edges) {
if (to->visited_from == nullptr) {
to->visited_from = node;
to_visit.Push(to);
}
}
}
}
/// Trace back along a path from `start` until finding a node that matches a predicate.
/// @param start the starting node
/// @param pred the predicate function
/// @returns the first node found that matches the predicate, or nullptr
template <typename F>
Node* TraceBackAlongPathUntil(Node* start, F&& pred) {
auto* current = start;
while (current) {
if (pred(current)) {
break;
}
current = current->visited_from;
}
return current;
}
/// Recursively descend through the function called by `call` and the functions that it calls in
/// order to find a call to a builtin function that requires uniformity with the given severity.
const ast::CallExpression* FindBuiltinThatRequiresUniformity(
const ast::CallExpression* call,
builtin::DiagnosticSeverity severity) {
auto* target = SemCall(call)->Target();
if (target->Is<sem::Builtin>()) {
// This is a call to a builtin, so we must be done.
return call;
} else if (auto* user = target->As<sem::Function>()) {
// This is a call to a user-defined function, so inspect the functions called by that
// function and look for one whose node has an edge from the RequiredToBeUniform node.
auto target_info = functions_.Find(user->Declaration());
for (auto* call_node : target_info->RequiredToBeUniform(severity)->edges) {
if (call_node->type == Node::kRegular) {
auto* child_call = call_node->ast->As<ast::CallExpression>();
return FindBuiltinThatRequiresUniformity(child_call, severity);
}
}
TINT_ASSERT(Resolver, false && "unable to find child call with uniformity requirement");
} else {
TINT_ASSERT(Resolver, false && "unexpected call expression type");
}
return nullptr;
}
/// Add diagnostic notes to show where control flow became non-uniform on the way to a node.
/// @param function the function being analyzed
/// @param required_to_be_uniform the node to traverse from
/// @param may_be_non_uniform the node to traverse to
void ShowControlFlowDivergence(FunctionInfo& function,
Node* required_to_be_uniform,
Node* may_be_non_uniform) {
// Traverse the graph to generate a path from the node to the source of non-uniformity.
function.ResetVisited();
Traverse(required_to_be_uniform);
// Get the source of the non-uniform value.
auto* non_uniform_source = may_be_non_uniform->visited_from;
TINT_ASSERT(Resolver, non_uniform_source);
// Show where the non-uniform value results in non-uniform control flow.
auto* control_flow = TraceBackAlongPathUntil(
non_uniform_source, [](Node* node) { return node->affects_control_flow; });
if (control_flow) {
diagnostics_.add_note(diag::System::Resolver,
"control flow depends on possibly non-uniform value",
control_flow->ast->source);
// TODO(jrprice): There are cases where the function with uniformity requirements is not
// actually inside this control flow construct, for example:
// - A conditional interrupt (e.g. break), with a barrier elsewhere in the loop
// - A conditional assignment to a variable, which is later used to guard a barrier
// In these cases, the diagnostics are not entirely accurate as they may not highlight
// the actual cause of divergence.
}
ShowSourceOfNonUniformity(non_uniform_source);
}
/// Add a diagnostic note to show the origin of a non-uniform value.
/// @param non_uniform_source the node that represents a non-uniform value
void ShowSourceOfNonUniformity(Node* non_uniform_source) {
TINT_ASSERT(Resolver, non_uniform_source);
auto var_type = [&](const sem::Variable* var) {
switch (var->AddressSpace()) {
case builtin::AddressSpace::kStorage:
return "read_write storage buffer ";
case builtin::AddressSpace::kWorkgroup:
return "workgroup storage variable ";
case builtin::AddressSpace::kPrivate:
return "module-scope private variable ";
default:
return "";
}
};
auto param_type = [&](const sem::Parameter* param) {
if (ast::HasAttribute<ast::BuiltinAttribute>(param->Declaration()->attributes)) {
return "builtin ";
} else if (ast::HasAttribute<ast::LocationAttribute>(
param->Declaration()->attributes)) {
return "user-defined input ";
} else {
return "parameter ";
}
};
// Show the source of the non-uniform value.
Switch(
non_uniform_source->ast,
[&](const ast::IdentifierExpression* ident) {
auto* var = sem_.GetVal(ident)->UnwrapLoad()->As<sem::VariableUser>()->Variable();
utils::StringStream ss;
if (auto* param = var->As<sem::Parameter>()) {
auto* func = param->Owner()->As<sem::Function>();
ss << param_type(param) << "'" << NameFor(ident) << "' of '" << NameFor(func)
<< "' may be non-uniform";
} else {
ss << "reading from " << var_type(var) << "'" << NameFor(ident)
<< "' may result in a non-uniform value";
}
diagnostics_.add_note(diag::System::Resolver, ss.str(), ident->source);
},
[&](const ast::Variable* v) {
auto* var = sem_.Get(v);
utils::StringStream ss;
ss << "reading from " << var_type(var) << "'" << NameFor(v)
<< "' may result in a non-uniform value";
diagnostics_.add_note(diag::System::Resolver, ss.str(), v->source);
},
[&](const ast::CallExpression* c) {
auto target_name = NameFor(c->target);
switch (non_uniform_source->type) {
case Node::kFunctionCallReturnValue: {
diagnostics_.add_note(
diag::System::Resolver,
"return value of '" + target_name + "' may be non-uniform", c->source);
break;
}
case Node::kFunctionCallArgumentContents: {
auto* arg = c->args[non_uniform_source->arg_index];
auto* var = sem_.GetVal(arg)->RootIdentifier();
utils::StringStream ss;
ss << "reading from " << var_type(var) << "'" << NameFor(var)
<< "' may result in a non-uniform value";
diagnostics_.add_note(diag::System::Resolver, ss.str(),
var->Declaration()->source);
break;
}
case Node::kFunctionCallArgumentValue: {
auto* arg = c->args[non_uniform_source->arg_index];
// TODO(jrprice): Which output? (return value vs another pointer argument).
diagnostics_.add_note(diag::System::Resolver,
"passing non-uniform pointer to '" + target_name +
"' may produce a non-uniform output",
arg->source);
break;
}
case Node::kFunctionCallPointerArgumentResult: {
diagnostics_.add_note(
diag::System::Resolver,
"contents of pointer may become non-uniform after calling '" +
target_name + "'",
c->args[non_uniform_source->arg_index]->source);
break;
}
default: {
TINT_ICE(Resolver, diagnostics_) << "unhandled source of non-uniformity";
break;
}
}
},
[&](const ast::Expression* e) {
diagnostics_.add_note(diag::System::Resolver,
"result of expression may be non-uniform", e->source);
},
[&](Default) {
TINT_ICE(Resolver, diagnostics_) << "unhandled source of non-uniformity";
});
}
/// Generate a diagnostic message for a uniformity issue.
/// @param function the function that the diagnostic is being produced for
/// @param source_node the node that has caused a uniformity issue in `function`
/// @param severity the severity of the diagnostic
void MakeError(FunctionInfo& function,
Node* source_node,
builtin::DiagnosticSeverity severity) {
// Helper to produce a diagnostic message, as a note or with the global failure severity.
auto report = [&](Source source, std::string msg, bool note) {
diag::Diagnostic error{};
error.severity = note ? diag::Severity::Note : builtin::ToSeverity(severity);
error.system = diag::System::Resolver;
error.source = source;
error.message = msg;
diagnostics_.add(std::move(error));
};
// Traverse the graph to generate a path from RequiredToBeUniform to the source node.
function.ResetVisited();
Traverse(function.RequiredToBeUniform(severity));
TINT_ASSERT(Resolver, source_node->visited_from);
// Find a node that is required to be uniform that has a path to the source node.
auto* cause = TraceBackAlongPathUntil(source_node, [&](Node* node) {
return node->visited_from == function.RequiredToBeUniform(severity);
});
// The node will always have a corresponding call expression.
auto* call = cause->ast->As<ast::CallExpression>();
TINT_ASSERT(Resolver, call);
auto* target = SemCall(call)->Target();
auto func_name = NameFor(call->target);
if (cause->type == Node::kFunctionCallArgumentValue ||
cause->type == Node::kFunctionCallArgumentContents) {
bool is_value = (cause->type == Node::kFunctionCallArgumentValue);
auto* user_func = target->As<sem::Function>();
if (user_func) {
// Recurse into the called function to show the reason for the requirement.
auto next_function = functions_.Find(user_func->Declaration());
auto& param_info = next_function->parameters[cause->arg_index];
MakeError(*next_function,
is_value ? param_info.value : param_info.ptr_input_contents, severity);
}
// Show the place where the non-uniform argument was passed.
// If this is a builtin, this will be the trigger location for the failure.
utils::StringStream ss;
ss << "possibly non-uniform value passed" << (is_value ? "" : " via pointer")
<< " here";
report(call->args[cause->arg_index]->source, ss.str(), /* note */ user_func != nullptr);
// Show the origin of non-uniformity for the value or data that is being passed.
ShowSourceOfNonUniformity(source_node->visited_from);
} else {
auto* builtin_call = FindBuiltinThatRequiresUniformity(call, severity);
{
// Show a builtin was reachable from this call (which may be the call itself).
// This will be the trigger location for the failure.
utils::StringStream ss;
ss << "'" << NameFor(builtin_call->target)
<< "' must only be called from uniform control flow";
report(builtin_call->source, ss.str(), /* note */ false);
}
if (builtin_call != call) {
// The call was to a user function, so show that call too.
utils::StringStream ss;
ss << "called ";
if (target->As<sem::Function>() != SemCall(builtin_call)->Stmt()->Function()) {
ss << "indirectly ";
}
ss << "by '" << func_name << "' from '" << function.name << "'";
report(call->source, ss.str(), /* note */ true);
}
// Show the point at which control-flow depends on a non-uniform value.
ShowControlFlowDivergence(function, cause, source_node);
}
}
// Helper for obtaining the sem::Call node for the ast::CallExpression
const sem::Call* SemCall(const ast::CallExpression* expr) const {
return sem_.Get(expr)->UnwrapMaterialize()->As<sem::Call>();
}
};
} // namespace
bool AnalyzeUniformity(ProgramBuilder* builder, const DependencyGraph& dependency_graph) {
UniformityGraph graph(builder);
return graph.Build(dependency_graph);
}
} // namespace tint::resolver
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