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Simplify OpPhi instructions referencing unreachable continues

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In dead branch elimination, we already recognize unreachable continue
blocks, and update OpPhi instruction accordingly.  This change adds an
extra check: if the head block has exactly 1 other incoming edge, then
replace the OpPhi with the value from that edge.

Fixes #1314.
This commit is contained in:
Steven Perron 2018-02-13 21:08:43 -05:00 committed by Steven Perron
parent 3756b387f3
commit 50f307f889
2 changed files with 61 additions and 16 deletions
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12
source/opt/dead_branch_elim_pass.cpp
View File

@ -211,12 +211,17 @@ bool DeadBranchElimPass::FixPhiNodesInLiveBlocks(
operands.push_back(inst->GetOperand(0u));
operands.push_back(inst->GetOperand(1u));
// Iterate through the incoming labels and determine which to keep
// and/or modify.
// and/or modify. If there in an unreachable continue block, there will
// be an edge from that block to the header. We need to keep it to
// maintain the structured control flow. If the header has more that 2
// incoming edges, then the OpPhi must have an entry for that edge.
// However, if there is only one other incoming edge, the OpPhi can be
// eliminated.
for (uint32_t i = 1; i < inst->NumInOperands(); i += 2) {
ir::BasicBlock* inc = GetParentBlock(inst->GetSingleWordInOperand(i));
auto cont_iter = unreachable_continues.find(inc);
if (cont_iter != unreachable_continues.end() &&
cont_iter->second == &block) {
cont_iter->second == &block && inst->NumInOperands() > 4) {
if (get_def_use_mgr()
->GetDef(inst->GetSingleWordInOperand(i - 1))
->opcode() == SpvOpUndef) {
@ -250,7 +255,8 @@ bool DeadBranchElimPass::FixPhiNodesInLiveBlocks(
modified = true;
uint32_t continue_id = block.ContinueBlockIdIfAny();
if (!backedge_added && continue_id != 0 &&
unreachable_continues.count(GetParentBlock(continue_id))) {
unreachable_continues.count(GetParentBlock(continue_id)) &&
operands.size() > 4) {
// Changed the backedge to branch from the continue block instead
// of a successor of the continue block. Add an entry to the phi to
// provide an undef for the continue block. Since the successor of

65
test/opt/dead_branch_elim_test.cpp
View File

@ -1415,13 +1415,11 @@ OpFunctionEnd
SinglePassRunAndMatch<opt::DeadBranchElimPass>(text, true);
}
TEST_F(DeadBranchElimTest, UnreachableLoopMergeAndContinueTargets) {
TEST_F(DeadBranchElimTest, RemovePhiWithUnreachableContinue) {
const std::string text = R"(
; CHECK: [[undef:%\w+]] = OpUndef %bool
; CHECK: [[entry:%\w+]] = OpLabel
; CHECK-NEXT: OpBranch [[header:%\w+]]
; CHECK: OpPhi %bool %false [[entry]] [[undef]] [[continue:%\w+]]
; CHECK-NEXT: OpLoopMerge [[merge:%\w+]] [[continue]] None
; CHECK: OpLoopMerge [[merge:%\w+]] [[continue:%\w+]] None
; CHECK-NEXT: OpBranch [[ret:%\w+]]
; CHECK-NEXT: [[ret]] = OpLabel
; CHECK-NEXT: OpReturn
@ -1458,6 +1456,54 @@ OpFunctionEnd
SinglePassRunAndMatch<opt::DeadBranchElimPass>(text, true);
}
TEST_F(DeadBranchElimTest, UnreachableLoopMergeAndContinueTargets) {
const std::string text = R"(
; CHECK: [[undef:%\w+]] = OpUndef %bool
; CHECK: OpSelectionMerge [[header:%\w+]]
; CHECK-NEXT: OpBranchConditional {{%\w+}} [[if_lab:%\w+]] [[else_lab:%\w+]]
; CHECK: OpPhi %bool %false [[if_lab]] %false [[else_lab]] [[undef]] [[continue:%\w+]]
; CHECK-NEXT: OpLoopMerge [[merge:%\w+]] [[continue]] None
; CHECK-NEXT: OpBranch [[ret:%\w+]]
; CHECK-NEXT: [[ret]] = OpLabel
; CHECK-NEXT: OpReturn
; CHECK: [[continue]] = OpLabel
; CHECK-NEXT: OpBranch [[header]]
; CHECK: [[merge]] = OpLabel
; CHECK-NEXT: OpUnreachable
OpCapability Kernel
OpCapability Linkage
OpMemoryModel Logical OpenCL
OpName %func "func"
OpDecorate %func LinkageAttributes "func" Export
%bool = OpTypeBool
%false = OpConstantFalse %bool
%true = OpConstantTrue %bool
%void = OpTypeVoid
%funcTy = OpTypeFunction %void
%func = OpFunction %void None %funcTy
%1 = OpLabel
%c = OpUndef %bool
OpSelectionMerge %2 None
OpBranchConditional %c %if %else
%if = OpLabel
OpBranch %2
%else = OpLabel
OpBranch %2
%2 = OpLabel
%phi = OpPhi %bool %false %if %false %else %true %continue
OpLoopMerge %merge %continue None
OpBranch %3
%3 = OpLabel
OpReturn
%continue = OpLabel
OpBranch %2
%merge = OpLabel
OpReturn
OpFunctionEnd
)";
SinglePassRunAndMatch<opt::DeadBranchElimPass>(text, true);
}
TEST_F(DeadBranchElimTest, EarlyReconvergence) {
const std::string text = R"(
; CHECK-NOT: OpBranchConditional
@ -1721,12 +1767,10 @@ OpFunctionEnd
TEST_F(DeadBranchElimTest, ExtraBackedgeBlocksUnreachable) {
const std::string text = R"(
; CHECK: [[undef:%\w+]] = OpUndef
; CHECK: [[entry:%\w+]] = OpLabel
; CHECK-NEXT: OpBranch [[header:%\w+]]
; CHECK-NEXT: [[header]] = OpLabel
; CHECK-NEXT: OpPhi %bool %true [[entry]] [[undef]] [[continue:%\w+]]
; CHECK-NEXT: OpLoopMerge [[merge:%\w+]] [[continue]] None
; CHECK-NEXT: OpLoopMerge [[merge:%\w+]] [[continue:%\w+]] None
; CHECK-NEXT: OpBranch [[merge]]
; CHECK-NEXT: [[continue]] = OpLabel
; CHECK-NEXT: OpBranch [[header]]
@ -1777,7 +1821,6 @@ OpEntryPoint Fragment %func "func"
%1 = OpLabel
OpBranch %2
%2 = OpLabel
%3 = OpPhi %bool %true %1 %undef %5
OpLoopMerge %4 %5 None
OpBranch %6
%6 = OpLabel
@ -1849,14 +1892,10 @@ OpFunctionEnd
TEST_F(DeadBranchElimTest, UnreachableContinuePhiInMerge) {
const std::string text = R"(
; CHECK: [[float_undef:%\w+]] = OpUndef %float
; CHECK: [[int_undef:%\w+]] = OpUndef %int
; CHECK: [[entry:%\w+]] = OpLabel
; CHECK-NEXT: OpBranch [[header:%\w+]]
; CHECK-NEXT: [[header]] = OpLabel
; CHECK-NEXT: OpPhi %float {{%\w+}} [[entry]] [[float_undef]] [[continue:%\w+]]
; CHECK-NEXT: OpPhi %int {{%\w+}} [[entry]] [[int_undef]] [[continue]]
; CHECK-NEXT: OpLoopMerge [[merge:%\w+]] [[continue]] None
; CHECK-NEXT: OpLoopMerge [[merge:%\w+]] [[continue:%\w+]] None
; CHECK-NEXT: OpBranch [[label:%\w+]]
; CHECK-NEXT: [[label]] = OpLabel
; CHECK-NEXT: [[fadd:%\w+]] = OpFAdd