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[spirv-reader] Hoist definitions as needed 

Compensate for the fact that dominance does not correspond
exactly to scoping. A definition can dominate a use, but when mapped
in a naive way to constant definitiion and its use, the definition
name goes out of scope by the time you reach the use.

This is correct for storable types.

Bug: tint:3
Change-Id: I03e6c5ba68393151485ed4cdbe6b2b3d7773d1ad
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/24141
Reviewed-by: dan sinclair <dsinclair@google.com>
This commit is contained in:
David Neto 2020-06-30 15:16:18 +00:00
parent de7b15ebb9
commit e91325956d
3 changed files with 235 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

71
src/reader/spirv/function.cc
View File

@ -624,7 +624,7 @@ bool FunctionEmitter::EmitBody() {
// TODO(dneto): register phis
// TODO(dneto): register SSA values which need to be hoisted
RegisterValuesNeedingNamedDefinition();
RegisterValuesNeedingNamedOrHoistedDefinition();
if (!EmitFunctionVariables()) {
return false;
@ -2361,6 +2361,19 @@ bool FunctionEmitter::EmitStatementsInBasicBlock(const BlockInfo& block_info,
// Only emit this part of the basic block once.
return true;
}
// Emit declarations of hoisted variables.
for (auto id : block_info.hoisted_ids) {
const auto* def_inst = def_use_mgr_->GetDef(id);
assert(def_inst);
AddStatement(
std::make_unique<ast::VariableDeclStatement>(parser_impl_.MakeVariable(
id, ast::StorageClass::kFunction,
parser_impl_.ConvertType(def_inst->type_id()))));
// Save this as an already-named value.
identifier_values_.insert(id);
}
const spvtools::opt::BasicBlock& bb = *(block_info.basic_block);
const auto* terminator = bb.terminator();
const auto* merge = bb.GetMergeInst(); // Might be nullptr
@ -2399,22 +2412,38 @@ bool FunctionEmitter::EmitConstDefinition(
return success();
}
bool FunctionEmitter::EmitConstDefOrWriteToHoistedVar(
const spvtools::opt::Instruction& inst,
TypedExpression ast_expr) {
const auto result_id = inst.result_id();
if (needs_hoisted_def_.count(result_id) != 0) {
// Emit an assignment of the expression to the hoisted variable.
AddStatement(std::make_unique<ast::AssignmentStatement>(
std::make_unique<ast::IdentifierExpression>(namer_.Name(result_id)),
std::move(ast_expr.expr)));
return true;
}
return EmitConstDefinition(inst, std::move(ast_expr));
}
bool FunctionEmitter::EmitStatement(const spvtools::opt::Instruction& inst) {
// Handle combinatorial instructions first.
const auto result_id = inst.result_id();
// Handle combinatorial instructions.
auto combinatorial_expr = MaybeEmitCombinatorialValue(inst);
if (combinatorial_expr.expr != nullptr) {
if ((needs_named_const_def_.count(inst.result_id()) == 0) &&
if ((needs_hoisted_def_.count(result_id) == 0) &&
(needs_named_const_def_.count(result_id) == 0) &&
(def_use_mgr_->NumUses(&inst) == 1)) {
// If it's used once, and doesn't need a named constant definition,
// then defer emitting the expression until it's used. Any supporting
// statements have already been emitted.
singly_used_values_.insert(
std::make_pair(inst.result_id(), std::move(combinatorial_expr)));
std::make_pair(result_id, std::move(combinatorial_expr)));
return success();
}
// Otherwise, generate a const definition for it now and later use
// the const's name at the uses of the value.
return EmitConstDefinition(inst, std::move(combinatorial_expr));
return EmitConstDefOrWriteToHoistedVar(inst, std::move(combinatorial_expr));
}
if (failed()) {
return false;
@ -2435,13 +2464,13 @@ bool FunctionEmitter::EmitStatement(const spvtools::opt::Instruction& inst) {
case SpvOpLoad:
// Memory accesses must be issued in SPIR-V program order.
// So represent a load by a new const definition.
return EmitConstDefinition(
return EmitConstDefOrWriteToHoistedVar(
inst, MakeExpression(inst.GetSingleWordInOperand(0)));
case SpvOpCopyObject:
// Arguably, OpCopyObject is purely combinatorial. On the other hand,
// it exists to make a new name for something. So we choose to make
// a new named constant definition.
return EmitConstDefinition(
return EmitConstDefOrWriteToHoistedVar(
inst, MakeExpression(inst.GetSingleWordInOperand(0)));
case SpvOpFunctionCall:
// TODO(dneto): Fill this out. Make this pass, for existing tests
@ -2876,7 +2905,7 @@ TypedExpression FunctionEmitter::MakeVectorShuffle(
result_type, std::move(values))};
}
void FunctionEmitter::RegisterValuesNeedingNamedDefinition() {
void FunctionEmitter::RegisterValuesNeedingNamedOrHoistedDefinition() {
// Maps a result ID to the block position where it is last used.
std::unordered_map<uint32_t, uint32_t> id_to_last_use_pos;
// List of pairs of (result id, block position of the definition).
@ -2930,12 +2959,32 @@ void FunctionEmitter::RegisterValuesNeedingNamedDefinition() {
auto last_use_where = id_to_last_use_pos.find(id);
if (last_use_where != id_to_last_use_pos.end()) {
const auto last_use_pos = last_use_where->second;
const auto* def_in_construct =
const auto* const def_in_construct =
GetBlockInfo(block_order_[def_pos])->construct;
const auto* last_use_in_construct =
const auto* const construct_with_last_use =
GetBlockInfo(block_order_[last_use_pos])->construct;
if (def_in_construct != last_use_in_construct) {
// Find the smallest structured construct that encloses the definition
// and all its uses.
const auto* enclosing_construct = def_in_construct;
while (enclosing_construct &&
!enclosing_construct->ContainsPos(last_use_pos)) {
enclosing_construct = enclosing_construct->parent;
}
// At worst, we go all the way out to the function construct.
assert(enclosing_construct != nullptr);
if (def_in_construct != construct_with_last_use) {
if (enclosing_construct == def_in_construct) {
// We can use a plain 'const' definition.
needs_named_const_def_.insert(id);
} else {
// We need to make a hoisted variable definition.
// TODO(dneto): Handle non-storable types, particularly pointers.
needs_hoisted_def_.insert(id);
auto* hoist_to_block = GetBlockInfo(enclosing_construct->begin_id);
hoist_to_block->hoisted_ids.push_back(id);
}
}
}
}

44
src/reader/spirv/function.h
View File

@ -157,6 +157,11 @@ struct BlockInfo {
/// This occurs when a block in this selection has both an if-break edge, and
/// also a different normal forward edge but without a merge instruction.
std::string flow_guard_name = "";
/// The result IDs that this block is responsible for declaring as a
/// hoisted variable. See the |needs_hoisted_def_| member of
/// FunctionEmitter for an explanation.
std::vector<uint32_t> hoisted_ids;
};
inline std::ostream& operator<<(std::ostream& o, const BlockInfo& bi) {
@ -278,11 +283,18 @@ class FunctionEmitter {
bool FindIfSelectionInternalHeaders();
/// Record the SPIR-V IDs of non-constants that should get a 'const'
/// definition in WGSL. This occurs when a SPIR-V instruction might use the
/// dynamically computed value only once, but the WGSL code might reference
/// it multiple times. For example, this occurs for the vector operands of
/// OpVectorShuffle. Populates |needs_named_const_def_|
void RegisterValuesNeedingNamedDefinition();
/// definition in WGSL, or a 'var' definition at an outer scope.
/// This occurs in several cases:
/// - When a SPIR-V instruction might use the dynamically computed value
/// only once, but the WGSL code might reference it multiple times.
/// For example, this occurs for the vector operands of OpVectorShuffle.
/// In this case the definition is added to |needs_named_const_def_|.
/// - When a definition and at least one of its uses are not in the
/// same structured construct.
/// In this case the definition is added to |needs_named_const_def_|.
/// - When a definition is in a construct that does not enclose all the
/// uses. In this case the definition is added to |needs_hoisted_def_|.
void RegisterValuesNeedingNamedOrHoistedDefinition();
/// Emits declarations of function variables.
/// @returns false if emission failed.
@ -431,6 +443,15 @@ class FunctionEmitter {
bool EmitConstDefinition(const spvtools::opt::Instruction& inst,
TypedExpression ast_expr);
/// Emits a write to a hoisted variable for the given SPIR-V id,
/// if that ID has a hoisted declaration. Otherwise, emits a const
/// definition instead.
/// @param inst the SPIR-V instruction defining the value
/// @param ast_expr the already-computed AST expression for the value
/// @returns false if emission failed.
bool EmitConstDefOrWriteToHoistedVar(const spvtools::opt::Instruction& inst,
TypedExpression ast_expr);
/// Makes an expression
/// @param id the SPIR-V ID of the value
/// @returns true if emission has not yet failed.
@ -603,6 +624,19 @@ class FunctionEmitter {
std::unordered_map<uint32_t, TypedExpression> singly_used_values_;
// Set of SPIR-V IDs which should get a named const definition.
std::unordered_set<uint32_t> needs_named_const_def_;
// The SPIR-V IDs that must be declared in WGSL before the corresponding
// location in SPIR-V. This compensates for the difference between dominance
// and scoping. An SSA definition can dominate all its uses, but the construct
// where it is defined does not enclose all the uses, and so if it were
// declared as a WGSL constant definition at the point of its SPIR-V
// definition, then the WGSL name would go out of scope too early. Fix that by
// creating a variable at the top of the smallest construct that encloses both
// the definition and all its uses. Then the original SPIR-V definition maps
// to a WGSL assignment to that variable, and each SPIR-V use becomes a WGSL
// read from the variable.
// TODO(dneto): This works for constants of storable type, but not, for
// example, pointers.
std::unordered_set<uint32_t> needs_hoisted_def_;
// The IDs of basic blocks, in reverse structured post-order (RSPO).
// This is the output order for the basic blocks.

135
src/reader/spirv/function_var_test.cc
View File

@ -61,9 +61,13 @@ std::string Preamble() {
%false = OpConstantFalse %bool
%float_0 = OpConstant %float 0.0
%float_1p5 = OpConstant %float 1.5
%uint_0 = OpConstant %uint 0
%uint_1 = OpConstant %uint 1
%int_m1 = OpConstant %int -1
%uint_2 = OpConstant %uint 2
%uint_3 = OpConstant %uint 3
%uint_4 = OpConstant %uint 4
%uint_5 = OpConstant %uint 5
%v2float = OpTypeVector %float 2
%m3v2float = OpTypeMatrix %v2float 3
@ -794,6 +798,137 @@ Return{}
)")) << ToString(fe.ast_body());
}
TEST_F(
SpvParserTest,
EmitStatement_CombinatorialNonPointer_DefConstruct_DoesNotEncloseAllUses) {
// Compensate for the difference between dominance and scoping.
// Exercise hoisting of the constant definition to before its natural
// location.
//
// The definition of %2 should be hoisted
auto assembly = Preamble() + R"(
%pty = OpTypePointer Private %uint
%1 = OpVariable %pty Private
%100 = OpFunction %void None %voidfn
%3 = OpLabel
OpStore %1 %uint_0
OpBranch %5
%5 = OpLabel
OpStore %1 %uint_1
OpLoopMerge %99 %80 None
OpBranchConditional %false %99 %20
%20 = OpLabel
OpStore %1 %uint_3
OpSelectionMerge %50 None
OpBranchConditional %true %30 %40
%30 = OpLabel
; This combinatorial definition in nested control flow dominates
; the use in the merge block in %50
%2 = OpIAdd %uint %uint_1 %uint_1
OpBranch %50
%40 = OpLabel
OpReturn
%50 = OpLabel ; merge block for if-selection
OpStore %1 %2
OpBranch %80
%80 = OpLabel ; merge block
OpStore %1 %uint_4
OpBranchConditional %false %99 %5 ; loop backedge
%99 = OpLabel
OpStore %1 %uint_5
OpReturn
OpFunctionEnd
)";
auto* p = parser(test::Assemble(assembly));
ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << assembly;
FunctionEmitter fe(p, *spirv_function(100));
EXPECT_TRUE(fe.EmitBody()) << p->error();
EXPECT_THAT(ToString(fe.ast_body()), Eq(R"(Assignment{
Identifier{x_1}
ScalarConstructor{0}
}
Loop{
VariableDeclStatement{
Variable{
x_2
function
__u32
}
}
Assignment{
Identifier{x_1}
ScalarConstructor{1}
}
If{
(
ScalarConstructor{false}
)
{
Break{}
}
}
Assignment{
Identifier{x_1}
ScalarConstructor{3}
}
If{
(
ScalarConstructor{true}
)
{
Assignment{
Identifier{x_2}
Binary{
ScalarConstructor{1}
add
ScalarConstructor{1}
}
}
}
}
Else{
{
Return{}
}
}
Assignment{
Identifier{x_1}
Identifier{x_2}
}
continuing {
Assignment{
Identifier{x_1}
ScalarConstructor{4}
}
If{
(
ScalarConstructor{false}
)
{
Break{}
}
}
}
}
Assignment{
Identifier{x_1}
ScalarConstructor{5}
}
Return{}
)")) << ToString(fe.ast_body());
}
} // namespace
} // namespace spirv
} // namespace reader