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Fix ADCE to treat OpUnreachable correctly during liveness analysis (#1984)

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ADCE liveness algorithm should treat OpUnreachable at least like other
branch instructions. It was being treated as always live which was
preventing useless structured constructs from being eliminated.
OpUnreachable is generated by dead branch elimination which is now
being required by merge return, so this fix should accompany that
change.
This commit is contained in:
greg-lunarg 2018-10-19 08:16:35 -06:00 committed by Steven Perron
parent 0e68bb3632
commit c4687889b7
2 changed files with 158 additions and 4 deletions
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10
source/opt/aggressive_dead_code_elim_pass.cpp
View File

@ -142,8 +142,9 @@ bool AggressiveDCEPass::AllExtensionsSupported() const {
bool AggressiveDCEPass::IsDead(Instruction* inst) {
if (IsLive(inst)) return false;
if (inst->IsBranch() && !IsStructuredHeader(context()->get_instr_block(inst),
nullptr, nullptr, nullptr))
if ((inst->IsBranch() || inst->opcode() == SpvOpUnreachable) &&
!IsStructuredHeader(context()->get_instr_block(inst), nullptr, nullptr,
nullptr))
return false;
return true;
}
@ -383,7 +384,8 @@ bool AggressiveDCEPass::AggressiveDCE(Function* func) {
} break;
case SpvOpSwitch:
case SpvOpBranch:
case SpvOpBranchConditional: {
case SpvOpBranchConditional:
case SpvOpUnreachable: {
if (assume_branches_live.top()) {
AddToWorklist(&*ii);
}
@ -462,7 +464,7 @@ bool AggressiveDCEPass::AggressiveDCE(Function* func) {
if (varId != 0) {
ProcessLoad(varId);
}
// If merge, add all other branches part of that control structure
// If merge, add other branches that are part of its control structure
} else if (liveInst->opcode() == SpvOpLoopMerge ||
liveInst->opcode() == SpvOpSelectionMerge) {
AddBreaksAndContinuesToWorklist(liveInst);

152
test/opt/aggressive_dead_code_elim_test.cpp
View File

@ -5930,6 +5930,158 @@ OpFunctionEnd
SinglePassRunAndCheck<AggressiveDCEPass>(test, test, true, true);
}
TEST_F(AggressiveDCETest, EliminateLoopWithUnreachable) {
// #version 430
//
// layout(std430) buffer U_t
// {
// float g_F[10];
// float g_S;
// };
//
// layout(location = 0)out float o;
//
// void main(void)
// {
// // Useless loop
// for (int i = 0; i<10; i++) {
// if (g_F[i] == 0.0)
// break;
// else
// break;
// // Unreachable merge block created here.
// // Need to edit SPIR-V to change to OpUnreachable
// }
// o = g_S;
// }
const std::string before =
R"(OpCapability Shader
%1 = OpExtInstImport "GLSL.std.450"
OpMemoryModel Logical GLSL450
OpEntryPoint Fragment %main "main" %o
OpExecutionMode %main OriginUpperLeft
OpSource GLSL 430
OpName %main "main"
OpName %i "i"
OpName %U_t "U_t"
OpMemberName %U_t 0 "g_F"
OpMemberName %U_t 1 "g_S"
OpName %_ ""
OpName %o "o"
OpDecorate %_arr_float_uint_10 ArrayStride 4
OpMemberDecorate %U_t 0 Offset 0
OpMemberDecorate %U_t 1 Offset 40
OpDecorate %U_t BufferBlock
OpDecorate %_ DescriptorSet 0
OpDecorate %o Location 0
%void = OpTypeVoid
%9 = OpTypeFunction %void
%int = OpTypeInt 32 1
%_ptr_Function_int = OpTypePointer Function %int
%int_0 = OpConstant %int 0
%int_10 = OpConstant %int 10
%bool = OpTypeBool
%float = OpTypeFloat 32
%uint = OpTypeInt 32 0
%uint_10 = OpConstant %uint 10
%_arr_float_uint_10 = OpTypeArray %float %uint_10
%U_t = OpTypeStruct %_arr_float_uint_10 %float
%_ptr_Uniform_U_t = OpTypePointer Uniform %U_t
%_ = OpVariable %_ptr_Uniform_U_t Uniform
%_ptr_Uniform_float = OpTypePointer Uniform %float
%float_0 = OpConstant %float 0
%int_1 = OpConstant %int 1
%_ptr_Output_float = OpTypePointer Output %float
%o = OpVariable %_ptr_Output_float Output
%main = OpFunction %void None %9
%23 = OpLabel
%i = OpVariable %_ptr_Function_int Function
OpStore %i %int_0
OpBranch %24
%24 = OpLabel
OpLoopMerge %25 %26 None
OpBranch %27
%27 = OpLabel
%28 = OpLoad %int %i
%29 = OpSLessThan %bool %28 %int_10
OpBranchConditional %29 %30 %25
%30 = OpLabel
%31 = OpLoad %int %i
%32 = OpAccessChain %_ptr_Uniform_float %_ %int_0 %31
%33 = OpLoad %float %32
%34 = OpFOrdEqual %bool %33 %float_0
OpSelectionMerge %35 None
OpBranchConditional %34 %36 %37
%36 = OpLabel
OpBranch %25
%37 = OpLabel
OpBranch %25
%35 = OpLabel
OpUnreachable
%26 = OpLabel
%38 = OpLoad %int %i
%39 = OpIAdd %int %38 %int_1
OpStore %i %39
OpBranch %24
%25 = OpLabel
%40 = OpAccessChain %_ptr_Uniform_float %_ %int_1
%41 = OpLoad %float %40
OpStore %o %41
OpReturn
OpFunctionEnd
)";
const std::string after =
R"(OpCapability Shader
%1 = OpExtInstImport "GLSL.std.450"
OpMemoryModel Logical GLSL450
OpEntryPoint Fragment %main "main" %o
OpExecutionMode %main OriginUpperLeft
OpSource GLSL 430
OpName %main "main"
OpName %U_t "U_t"
OpMemberName %U_t 0 "g_F"
OpMemberName %U_t 1 "g_S"
OpName %_ ""
OpName %o "o"
OpDecorate %_arr_float_uint_10 ArrayStride 4
OpMemberDecorate %U_t 0 Offset 0
OpMemberDecorate %U_t 1 Offset 40
OpDecorate %U_t BufferBlock
OpDecorate %_ DescriptorSet 0
OpDecorate %o Location 0
%void = OpTypeVoid
%9 = OpTypeFunction %void
%int = OpTypeInt 32 1
%float = OpTypeFloat 32
%uint = OpTypeInt 32 0
%uint_10 = OpConstant %uint 10
%_arr_float_uint_10 = OpTypeArray %float %uint_10
%U_t = OpTypeStruct %_arr_float_uint_10 %float
%_ptr_Uniform_U_t = OpTypePointer Uniform %U_t
%_ = OpVariable %_ptr_Uniform_U_t Uniform
%_ptr_Uniform_float = OpTypePointer Uniform %float
%int_1 = OpConstant %int 1
%_ptr_Output_float = OpTypePointer Output %float
%o = OpVariable %_ptr_Output_float Output
%main = OpFunction %void None %9
%23 = OpLabel
OpBranch %24
%24 = OpLabel
OpBranch %25
%25 = OpLabel
%40 = OpAccessChain %_ptr_Uniform_float %_ %int_1
%41 = OpLoad %float %40
OpStore %o %41
OpReturn
OpFunctionEnd
)";
SetAssembleOptions(SPV_TEXT_TO_BINARY_OPTION_PRESERVE_NUMERIC_IDS);
SinglePassRunAndCheck<AggressiveDCEPass>(before, after, true, true);
}
TEST_F(AggressiveDCETest, DeadHlslCounterBufferGOOGLE) {
// We are able to remove "local2" because it is not loaded, but have to keep
// the stores to "local1".