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[IR] Track inbound branches to flow nodes. 

This CL updates the flow node to track the nodes which are inbound
to the current target. This allows to fix an issue with a loop,
after a continuing with a break, properly eliminating dead code.

This also allows always providing the merge target for an if, it
just knows if it's disconnected by having zero inbound branches.

Bug: tint:1718
Change-Id: Ia9b9dbc734bf1e9cd0c829093c0cb1e470efb32e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/107800
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
This commit is contained in:
dan sinclair 2022-11-01 14:22:10 +00:00 committed by Dawn LUCI CQ
parent 6c5db2afa6
commit b9ed75cf2f
7 changed files with 310 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
src/tint/ir/builder.cc
View File

@ -39,19 +39,23 @@ Function* Builder::CreateFunction(const ast::Function* ast_func) {
auto* ir_func = ir.flow_nodes.Create<Function>(ast_func); auto* ir_func = ir.flow_nodes.Create<Function>(ast_func);
ir_func->start_target = CreateBlock(); ir_func->start_target = CreateBlock();
ir_func->end_target = CreateTerminator(); ir_func->end_target = CreateTerminator();
// Function is always branching into the start target
ir_func->start_target->inbound_branches.Push(ir_func);
return ir_func; return ir_func;
} }
If* Builder::CreateIf(const ast::Statement* stmt, IfFlags flags) { If* Builder::CreateIf(const ast::Statement* stmt) {
auto* ir_if = ir.flow_nodes.Create<If>(stmt); auto* ir_if = ir.flow_nodes.Create<If>(stmt);
ir_if->false_target = CreateBlock();
ir_if->true_target = CreateBlock(); ir_if->true_target = CreateBlock();
ir_if->false_target = CreateBlock();
if (flags == IfFlags::kCreateMerge) {
ir_if->merge_target = CreateBlock(); ir_if->merge_target = CreateBlock();
} else {
ir_if->merge_target = nullptr; // An if always branches to both the true and false block.
} ir_if->true_target->inbound_branches.Push(ir_if);
ir_if->false_target->inbound_branches.Push(ir_if);
return ir_if; return ir_if;
} }
@ -61,13 +65,17 @@ Loop* Builder::CreateLoop(const ast::LoopStatement* stmt) {
ir_loop->continuing_target = CreateBlock(); ir_loop->continuing_target = CreateBlock();
ir_loop->merge_target = CreateBlock(); ir_loop->merge_target = CreateBlock();
// A loop always branches to the start block.
ir_loop->start_target->inbound_branches.Push(ir_loop);
return ir_loop; return ir_loop;
} }
void Builder::Branch(Block* from, const FlowNode* to) { void Builder::Branch(Block* from, FlowNode* to) {
TINT_ASSERT(IR, from); TINT_ASSERT(IR, from);
TINT_ASSERT(IR, to); TINT_ASSERT(IR, to);
from->branch_target = to; from->branch_target = to;
to->inbound_branches.Push(from);
} }
} // namespace tint::ir } // namespace tint::ir

14
src/tint/ir/builder.h
View File

@ -52,20 +52,10 @@ class Builder {
/// @returns the flow node /// @returns the flow node
Function* CreateFunction(const ast::Function* func); Function* CreateFunction(const ast::Function* func);
/// Flags used for creation of if flow nodes
enum class IfFlags {
/// Do not create a merge node, `merge_target` will be `nullptr`
kSkipMerge,
/// Create the `merge_target` block
kCreateMerge,
};
/// Creates an if flow node for the given ast::IfStatement or ast::BreakIfStatement /// Creates an if flow node for the given ast::IfStatement or ast::BreakIfStatement
/// @param stmt the ast::IfStatement or ast::BreakIfStatement /// @param stmt the ast::IfStatement or ast::BreakIfStatement
/// @param flags the if creation flags. By default the merge block will not be created, pass
/// IfFlags::kCreateMerge if creation is desired.
/// @returns the flow node /// @returns the flow node
If* CreateIf(const ast::Statement* stmt, IfFlags flags = IfFlags::kSkipMerge); If* CreateIf(const ast::Statement* stmt);
/// Creates a loop flow node for the given ast::LoopStatement /// Creates a loop flow node for the given ast::LoopStatement
/// @param stmt the ast::LoopStatement /// @param stmt the ast::LoopStatement
@ -75,7 +65,7 @@ class Builder {
/// Branches the given block to the given flow node. /// Branches the given block to the given flow node.
/// @param from the block to branch from /// @param from the block to branch from
/// @param to the node to branch too /// @param to the node to branch too
void Branch(Block* from, const FlowNode* to); void Branch(Block* from, FlowNode* to);
/// The IR module. /// The IR module.
Module ir; Module ir;

48
src/tint/ir/builder_impl.cc
View File

@ -50,23 +50,41 @@ class FlowStackScope {
BuilderImpl* impl_; BuilderImpl* impl_;
}; };
bool IsBranched(const Block* b) {
return b->branch_target != nullptr;
}
bool IsConnected(const FlowNode* b) {
// Function is always connected as it's the start.
if (b->Is<ir::Function>()) {
return true;
}
for (auto* parent : b->inbound_branches) {
if (IsConnected(parent)) {
return true;
}
}
// Getting here means all the incoming branches are disconnected.
return false;
}
} // namespace } // namespace
BuilderImpl::BuilderImpl(const Program* program) : builder_(program) {} BuilderImpl::BuilderImpl(const Program* program) : builder_(program) {}
BuilderImpl::~BuilderImpl() = default; BuilderImpl::~BuilderImpl() = default;
void BuilderImpl::BranchTo(const FlowNode* node) { void BuilderImpl::BranchTo(FlowNode* node) {
TINT_ASSERT(IR, current_flow_block_); TINT_ASSERT(IR, current_flow_block_);
TINT_ASSERT(IR, !current_flow_block_->branch_target); TINT_ASSERT(IR, !IsBranched(current_flow_block_));
builder_.Branch(current_flow_block_, node); builder_.Branch(current_flow_block_, node);
current_flow_block_->branch_target = node;
current_flow_block_ = nullptr; current_flow_block_ = nullptr;
} }
void BuilderImpl::BranchToIfNeeded(const FlowNode* node) { void BuilderImpl::BranchToIfNeeded(FlowNode* node) {
if (!current_flow_block_ || current_flow_block_->branch_target) { if (!current_flow_block_ || IsBranched(current_flow_block_)) {
return; return;
} }
BranchTo(node); BranchTo(node);
@ -168,7 +186,7 @@ bool BuilderImpl::EmitStatements(utils::VectorRef<const ast::Statement*> stmts)
// If the current flow block has a branch target then the rest of the statements in this // If the current flow block has a branch target then the rest of the statements in this
// block are dead code. Skip them. // block are dead code. Skip them.
if (!current_flow_block_ || current_flow_block_->branch_target) { if (!current_flow_block_ || IsBranched(current_flow_block_)) {
break; break;
} }
} }
@ -239,20 +257,19 @@ bool BuilderImpl::EmitIf(const ast::IfStatement* stmt) {
// If both branches went somewhere, then they both returned, continued or broke. So, // If both branches went somewhere, then they both returned, continued or broke. So,
// there is no need for the if merge-block and there is nothing to branch to the merge // there is no need for the if merge-block and there is nothing to branch to the merge
// block anyway. // block anyway.
if (if_node->true_target->branch_target && if_node->false_target->branch_target) { if (IsBranched(if_node->true_target) && IsBranched(if_node->false_target)) {
return true; return true;
} }
if_node->merge_target = builder_.CreateBlock();
current_flow_block_ = if_node->merge_target; current_flow_block_ = if_node->merge_target;
// If the true branch did not execute control flow, then go to the merge target // If the true branch did not execute control flow, then go to the merge target
if (!if_node->true_target->branch_target) { if (!IsBranched(if_node->true_target)) {
if_node->true_target->branch_target = if_node->merge_target; builder_.Branch(if_node->true_target, if_node->merge_target);
} }
// If the false branch did not execute control flow, then go to the merge target // If the false branch did not execute control flow, then go to the merge target
if (!if_node->false_target->branch_target) { if (!IsBranched(if_node->false_target)) {
if_node->false_target->branch_target = if_node->merge_target; builder_.Branch(if_node->false_target, if_node->merge_target);
} }
return true; return true;
@ -287,7 +304,12 @@ bool BuilderImpl::EmitLoop(const ast::LoopStatement* stmt) {
BranchToIfNeeded(loop_node->start_target); BranchToIfNeeded(loop_node->start_target);
} }
// The loop merge can get disconnected if the loop returns directly, or the continuing target
// branches, eventually, to the merge, but nothing branched to the continuing target.
current_flow_block_ = loop_node->merge_target; current_flow_block_ = loop_node->merge_target;
if (!IsConnected(loop_node->merge_target)) {
current_flow_block_ = nullptr;
}
return true; return true;
} }
@ -337,7 +359,7 @@ bool BuilderImpl::EmitContinue(const ast::ContinueStatement*) {
} }
bool BuilderImpl::EmitBreakIf(const ast::BreakIfStatement* stmt) { bool BuilderImpl::EmitBreakIf(const ast::BreakIfStatement* stmt) {
auto* if_node = builder_.CreateIf(stmt, Builder::IfFlags::kCreateMerge); auto* if_node = builder_.CreateIf(stmt);
// TODO(dsinclair): Emit the condition expression into the current block // TODO(dsinclair): Emit the condition expression into the current block

4
src/tint/ir/builder_impl.h
View File

@ -133,8 +133,8 @@ class BuilderImpl {
private: private:
enum class ControlFlags { kNone, kExcludeSwitch }; enum class ControlFlags { kNone, kExcludeSwitch };
void BranchTo(const ir::FlowNode* node); void BranchTo(ir::FlowNode* node);
void BranchToIfNeeded(const ir::FlowNode* node); void BranchToIfNeeded(ir::FlowNode* node);
FlowNode* FindEnclosingControl(ControlFlags flags); FlowNode* FindEnclosingControl(ControlFlags flags);

249
src/tint/ir/builder_impl_test.cc
View File

@ -36,6 +36,9 @@ TEST_F(IRBuilderImplTest, Func) {
EXPECT_NE(f->start_target, nullptr); EXPECT_NE(f->start_target, nullptr);
EXPECT_NE(f->end_target, nullptr); EXPECT_NE(f->end_target, nullptr);
EXPECT_EQ(1u, f->start_target->inbound_branches.Length());
EXPECT_EQ(1u, f->end_target->inbound_branches.Length());
EXPECT_EQ(f->start_target->branch_target, f->end_target); EXPECT_EQ(f->start_target->branch_target, f->end_target);
} }
@ -82,6 +85,13 @@ TEST_F(IRBuilderImplTest, IfStatement) {
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, flow->inbound_branches.Length());
EXPECT_EQ(1u, flow->true_target->inbound_branches.Length());
EXPECT_EQ(1u, flow->false_target->inbound_branches.Length());
EXPECT_EQ(2u, flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(1u, func->end_target->inbound_branches.Length());
EXPECT_EQ(func->start_target->branch_target, flow); EXPECT_EQ(func->start_target->branch_target, flow);
EXPECT_EQ(flow->true_target->branch_target, flow->merge_target); EXPECT_EQ(flow->true_target->branch_target, flow->merge_target);
EXPECT_EQ(flow->false_target->branch_target, flow->merge_target); EXPECT_EQ(flow->false_target->branch_target, flow->merge_target);
@ -116,6 +126,13 @@ TEST_F(IRBuilderImplTest, IfStatement_TrueReturns) {
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, flow->inbound_branches.Length());
EXPECT_EQ(1u, flow->true_target->inbound_branches.Length());
EXPECT_EQ(1u, flow->false_target->inbound_branches.Length());
EXPECT_EQ(1u, flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(2u, func->end_target->inbound_branches.Length());
EXPECT_EQ(func->start_target->branch_target, flow); EXPECT_EQ(func->start_target->branch_target, flow);
EXPECT_EQ(flow->true_target->branch_target, func->end_target); EXPECT_EQ(flow->true_target->branch_target, func->end_target);
EXPECT_EQ(flow->false_target->branch_target, flow->merge_target); EXPECT_EQ(flow->false_target->branch_target, flow->merge_target);
@ -150,6 +167,13 @@ TEST_F(IRBuilderImplTest, IfStatement_FalseReturns) {
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, flow->inbound_branches.Length());
EXPECT_EQ(1u, flow->true_target->inbound_branches.Length());
EXPECT_EQ(1u, flow->false_target->inbound_branches.Length());
EXPECT_EQ(1u, flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(2u, func->end_target->inbound_branches.Length());
EXPECT_EQ(func->start_target->branch_target, flow); EXPECT_EQ(func->start_target->branch_target, flow);
EXPECT_EQ(flow->true_target->branch_target, flow->merge_target); EXPECT_EQ(flow->true_target->branch_target, flow->merge_target);
EXPECT_EQ(flow->false_target->branch_target, func->end_target); EXPECT_EQ(flow->false_target->branch_target, func->end_target);
@ -179,14 +203,21 @@ TEST_F(IRBuilderImplTest, IfStatement_BothReturn) {
auto* flow = ir_if->As<ir::If>(); auto* flow = ir_if->As<ir::If>();
ASSERT_NE(flow->true_target, nullptr); ASSERT_NE(flow->true_target, nullptr);
ASSERT_NE(flow->false_target, nullptr); ASSERT_NE(flow->false_target, nullptr);
ASSERT_NE(flow->merge_target, nullptr);
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, flow->inbound_branches.Length());
EXPECT_EQ(1u, flow->true_target->inbound_branches.Length());
EXPECT_EQ(1u, flow->false_target->inbound_branches.Length());
EXPECT_EQ(0u, flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(2u, func->end_target->inbound_branches.Length());
EXPECT_EQ(func->start_target->branch_target, flow); EXPECT_EQ(func->start_target->branch_target, flow);
EXPECT_EQ(flow->true_target->branch_target, func->end_target); EXPECT_EQ(flow->true_target->branch_target, func->end_target);
EXPECT_EQ(flow->false_target->branch_target, func->end_target); EXPECT_EQ(flow->false_target->branch_target, func->end_target);
EXPECT_EQ(flow->merge_target, nullptr);
} }
TEST_F(IRBuilderImplTest, Loop_WithBreak) { TEST_F(IRBuilderImplTest, Loop_WithBreak) {
@ -214,6 +245,13 @@ TEST_F(IRBuilderImplTest, Loop_WithBreak) {
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, flow->inbound_branches.Length());
EXPECT_EQ(2u, flow->start_target->inbound_branches.Length());
EXPECT_EQ(0u, flow->continuing_target->inbound_branches.Length());
EXPECT_EQ(1u, flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(1u, func->end_target->inbound_branches.Length());
EXPECT_EQ(func->start_target->branch_target, flow); EXPECT_EQ(func->start_target->branch_target, flow);
EXPECT_EQ(flow->start_target->branch_target, flow->merge_target); EXPECT_EQ(flow->start_target->branch_target, flow->merge_target);
EXPECT_EQ(flow->continuing_target->branch_target, flow->start_target); EXPECT_EQ(flow->continuing_target->branch_target, flow->start_target);
@ -260,6 +298,17 @@ TEST_F(IRBuilderImplTest, Loop_WithContinue) {
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, loop_flow->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow->start_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow->continuing_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->true_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->false_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(1u, func->end_target->inbound_branches.Length());
EXPECT_EQ(func->start_target->branch_target, loop_flow); EXPECT_EQ(func->start_target->branch_target, loop_flow);
EXPECT_EQ(loop_flow->start_target->branch_target, if_flow); EXPECT_EQ(loop_flow->start_target->branch_target, if_flow);
EXPECT_EQ(if_flow->true_target->branch_target, loop_flow->merge_target); EXPECT_EQ(if_flow->true_target->branch_target, loop_flow->merge_target);
@ -308,6 +357,17 @@ TEST_F(IRBuilderImplTest, Loop_WithContinuing_BreakIf) {
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, loop_flow->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow->start_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow->continuing_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, break_if_flow->inbound_branches.Length());
EXPECT_EQ(1u, break_if_flow->true_target->inbound_branches.Length());
EXPECT_EQ(1u, break_if_flow->false_target->inbound_branches.Length());
EXPECT_EQ(1u, break_if_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(1u, func->end_target->inbound_branches.Length());
EXPECT_EQ(func->start_target->branch_target, loop_flow); EXPECT_EQ(func->start_target->branch_target, loop_flow);
EXPECT_EQ(loop_flow->start_target->branch_target, loop_flow->continuing_target); EXPECT_EQ(loop_flow->start_target->branch_target, loop_flow->continuing_target);
EXPECT_EQ(loop_flow->continuing_target->branch_target, break_if_flow); EXPECT_EQ(loop_flow->continuing_target->branch_target, break_if_flow);
@ -325,7 +385,7 @@ TEST_F(IRBuilderImplTest, Loop_WithReturn) {
// [if false] -> if merge // [if false] -> if merge
// [if merge] -> loop continuing // [if merge] -> loop continuing
// [loop continuing] -> loop start // [loop continuing] -> loop start
// [loop merge] -> func end // [loop merge] -> nullptr
// //
auto* ast_if = If(true, Block(Return())); auto* ast_if = If(true, Block(Return()));
auto* ast_loop = Loop(Block(ast_if, Continue())); auto* ast_loop = Loop(Block(ast_if, Continue()));
@ -357,14 +417,147 @@ TEST_F(IRBuilderImplTest, Loop_WithReturn) {
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, loop_flow->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow->start_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow->continuing_target->inbound_branches.Length());
EXPECT_EQ(0u, loop_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->true_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->false_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(1u, func->end_target->inbound_branches.Length());
EXPECT_EQ(loop_flow->start_target->branch_target, if_flow); EXPECT_EQ(loop_flow->start_target->branch_target, if_flow);
EXPECT_EQ(if_flow->true_target->branch_target, func->end_target); EXPECT_EQ(if_flow->true_target->branch_target, func->end_target);
EXPECT_EQ(if_flow->false_target->branch_target, if_flow->merge_target); EXPECT_EQ(if_flow->false_target->branch_target, if_flow->merge_target);
EXPECT_EQ(loop_flow->continuing_target->branch_target, loop_flow->start_target); EXPECT_EQ(loop_flow->continuing_target->branch_target, loop_flow->start_target);
EXPECT_EQ(func->start_target->branch_target, ir_loop); EXPECT_EQ(func->start_target->branch_target, ir_loop);
EXPECT_EQ(loop_flow->merge_target->branch_target, func->end_target); EXPECT_EQ(loop_flow->merge_target->branch_target, nullptr);
}
TEST_F(IRBuilderImplTest, Loop_WithOnlyReturn) {
// {
// loop {
// return;
// continue;
// }
// if true { return; }
// }
//
// func -> start -> loop -> loop start -> return -> func end
//
// [loop continuing] -> loop start
// [loop merge] -> nullptr
//
// Note, the continue; is here is a dead call, so we won't emit a branch to the continuing block
// so the inbound_branches will be zero for continuing.
//
// The `if` after the `loop` is also eliminated as there is no control-flow path reaching the
// block.
auto* ast_loop = Loop(Block(Return(), Continue()));
WrapInFunction(ast_loop, If(true, Block(Return())));
auto& b = Build();
auto r = b.Build();
ASSERT_TRUE(r) << b.error();
auto m = r.Move();
auto* ir_loop = b.FlowNodeForAstNode(ast_loop);
ASSERT_NE(ir_loop, nullptr);
EXPECT_TRUE(ir_loop->Is<ir::Loop>());
auto* loop_flow = ir_loop->As<ir::Loop>();
ASSERT_NE(loop_flow->start_target, nullptr);
ASSERT_NE(loop_flow->continuing_target, nullptr);
ASSERT_NE(loop_flow->merge_target, nullptr);
ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0];
EXPECT_EQ(1u, loop_flow->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow->start_target->inbound_branches.Length());
EXPECT_EQ(0u, loop_flow->continuing_target->inbound_branches.Length());
EXPECT_EQ(0u, loop_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(1u, func->end_target->inbound_branches.Length());
EXPECT_EQ(loop_flow->start_target->branch_target, func->end_target);
EXPECT_EQ(loop_flow->continuing_target->branch_target, loop_flow->start_target);
EXPECT_EQ(func->start_target->branch_target, ir_loop);
}
TEST_F(IRBuilderImplTest, Loop_WithOnlyReturn_ContinuingBreakIf) {
// {
// loop {
// return;
// continuing {
// break if true;
// }
// }
// if (true) { return; }
// }
//
// func -> start -> loop -> loop start -> return -> func end
//
// [loop continuing] -> break if true
// -> break if false
// [break if true] -> loop merge
// [break if false] -> if merge
// [break if merge] -> loop start
// [loop merge] -> nullptr
//
// In this case, the continuing block is dead code, but we don't really know that when parsing
// so we end up with a branch into the loop merge target. The loop merge can tell it's dead code
// so we can drop the if ater the loop.
auto* ast_break_if = BreakIf(true);
auto* ast_loop = Loop(Block(Return()), Block(ast_break_if));
auto* ast_if = If(true, Block(Return()));
WrapInFunction(Block(ast_loop, ast_if));
auto& b = Build();
auto r = b.Build();
ASSERT_TRUE(r) << b.error();
auto m = r.Move();
auto* ir_loop = b.FlowNodeForAstNode(ast_loop);
ASSERT_NE(ir_loop, nullptr);
EXPECT_TRUE(ir_loop->Is<ir::Loop>());
auto* loop_flow = ir_loop->As<ir::Loop>();
ASSERT_NE(loop_flow->start_target, nullptr);
ASSERT_NE(loop_flow->continuing_target, nullptr);
ASSERT_NE(loop_flow->merge_target, nullptr);
auto* ir_if = b.FlowNodeForAstNode(ast_if);
EXPECT_EQ(ir_if, nullptr);
auto* ir_break_if = b.FlowNodeForAstNode(ast_break_if);
ASSERT_NE(ir_break_if, nullptr);
EXPECT_TRUE(ir_break_if->Is<ir::If>());
auto* break_if_flow = ir_break_if->As<ir::If>();
ASSERT_NE(break_if_flow->true_target, nullptr);
ASSERT_NE(break_if_flow->false_target, nullptr);
ASSERT_NE(break_if_flow->merge_target, nullptr);
ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0];
EXPECT_EQ(1u, loop_flow->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow->start_target->inbound_branches.Length());
EXPECT_EQ(0u, loop_flow->continuing_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
// This is 1 because only the loop branch happens. The subsequent if return is dead code.
EXPECT_EQ(1u, func->end_target->inbound_branches.Length());
EXPECT_EQ(loop_flow->start_target->branch_target, func->end_target);
EXPECT_EQ(loop_flow->continuing_target->branch_target, break_if_flow);
EXPECT_EQ(func->start_target->branch_target, ir_loop);
} }
TEST_F(IRBuilderImplTest, Loop_WithIf_BothBranchesBreak) { TEST_F(IRBuilderImplTest, Loop_WithIf_BothBranchesBreak) {
@ -402,10 +595,22 @@ TEST_F(IRBuilderImplTest, Loop_WithIf_BothBranchesBreak) {
auto* if_flow = ir_if->As<ir::If>(); auto* if_flow = ir_if->As<ir::If>();
ASSERT_NE(if_flow->true_target, nullptr); ASSERT_NE(if_flow->true_target, nullptr);
ASSERT_NE(if_flow->false_target, nullptr); ASSERT_NE(if_flow->false_target, nullptr);
ASSERT_NE(if_flow->merge_target, nullptr);
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, loop_flow->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow->start_target->inbound_branches.Length());
EXPECT_EQ(0u, loop_flow->continuing_target->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->true_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow->false_target->inbound_branches.Length());
EXPECT_EQ(0u, if_flow->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(1u, func->end_target->inbound_branches.Length());
// Note, the `continue` is dead code because both if branches go out of loop, so it just gets // Note, the `continue` is dead code because both if branches go out of loop, so it just gets
// dropped. // dropped.
@ -413,7 +618,6 @@ TEST_F(IRBuilderImplTest, Loop_WithIf_BothBranchesBreak) {
EXPECT_EQ(loop_flow->start_target->branch_target, if_flow); EXPECT_EQ(loop_flow->start_target->branch_target, if_flow);
EXPECT_EQ(if_flow->true_target->branch_target, loop_flow->merge_target); EXPECT_EQ(if_flow->true_target->branch_target, loop_flow->merge_target);
EXPECT_EQ(if_flow->false_target->branch_target, loop_flow->merge_target); EXPECT_EQ(if_flow->false_target->branch_target, loop_flow->merge_target);
EXPECT_EQ(if_flow->merge_target, nullptr);
EXPECT_EQ(loop_flow->continuing_target->branch_target, loop_flow->start_target); EXPECT_EQ(loop_flow->continuing_target->branch_target, loop_flow->start_target);
EXPECT_EQ(loop_flow->merge_target->branch_target, func->end_target); EXPECT_EQ(loop_flow->merge_target->branch_target, func->end_target);
} }
@ -551,6 +755,41 @@ TEST_F(IRBuilderImplTest, Loop_Nested) {
ASSERT_EQ(1u, m.functions.Length()); ASSERT_EQ(1u, m.functions.Length());
auto* func = m.functions[0]; auto* func = m.functions[0];
EXPECT_EQ(1u, loop_flow_a->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow_a->start_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow_a->continuing_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow_a->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow_b->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow_b->start_target->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow_b->continuing_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow_b->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow_c->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow_c->start_target->inbound_branches.Length());
EXPECT_EQ(0u, loop_flow_c->continuing_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow_c->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow_d->inbound_branches.Length());
EXPECT_EQ(2u, loop_flow_d->start_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow_d->continuing_target->inbound_branches.Length());
EXPECT_EQ(1u, loop_flow_d->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_a->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_a->true_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_a->false_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_a->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_b->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_b->true_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_b->false_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_b->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_c->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_c->true_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_c->false_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_c->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_d->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_d->true_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_d->false_target->inbound_branches.Length());
EXPECT_EQ(1u, if_flow_d->merge_target->inbound_branches.Length());
EXPECT_EQ(1u, func->start_target->inbound_branches.Length());
EXPECT_EQ(1u, func->end_target->inbound_branches.Length());
EXPECT_EQ(func->start_target->branch_target, loop_flow_a); EXPECT_EQ(func->start_target->branch_target, loop_flow_a);
EXPECT_EQ(loop_flow_a->start_target->branch_target, loop_flow_b); EXPECT_EQ(loop_flow_a->start_target->branch_target, loop_flow_b);
EXPECT_EQ(loop_flow_b->start_target->branch_target, if_flow_a); EXPECT_EQ(loop_flow_b->start_target->branch_target, if_flow_a);

8
src/tint/ir/flow_node.h
View File

@ -16,6 +16,7 @@
#define SRC_TINT_IR_FLOW_NODE_H_ #define SRC_TINT_IR_FLOW_NODE_H_
#include "src/tint/castable.h" #include "src/tint/castable.h"
#include "src/tint/utils/vector.h"
namespace tint::ir { namespace tint::ir {
@ -24,6 +25,13 @@ class FlowNode : public Castable<FlowNode> {
public: public:
~FlowNode() override; ~FlowNode() override;
/// The list of flow nodes which branch into this node. This list maybe empty for several
/// reasons:
/// - Node is a start node
/// - Node is a merge target outside control flow (if that returns in both branches)
/// - Node is a continue target outside control flow (loop that returns)
utils::Vector<FlowNode*, 2> inbound_branches;
protected: protected:
/// Constructor /// Constructor
FlowNode(); FlowNode();

6
src/tint/ir/if.h
View File

@ -25,8 +25,7 @@ class Block;
namespace tint::ir { namespace tint::ir {
/// A flow node representing an if statement. The node always contains a true and a false block. It /// A flow node representing an if statement.
/// may contain a merge block where the true/false blocks will merge too unless they return.
class If : public Castable<If, FlowNode> { class If : public Castable<If, FlowNode> {
public: public:
/// Constructor /// Constructor
@ -41,7 +40,8 @@ class If : public Castable<If, FlowNode> {
Block* true_target = nullptr; Block* true_target = nullptr;
/// The false branch block /// The false branch block
Block* false_target = nullptr; Block* false_target = nullptr;
/// An optional block where the true/false blocks will branch too if needed. /// An block to reconvert the true/false barnches. The block always exists, but there maybe no
/// branches into it. (e.g. if both branches `return`)
Block* merge_target = nullptr; Block* merge_target = nullptr;
}; };