Handle dead infinite loops in DCE (#2471)
Fixes #2456
* When eliminating a structured construct that has an unreachable merge,
replace that unreachable terminator with an appropriate return
* New tests
diff --git a/source/opt/aggressive_dead_code_elim_pass.cpp b/source/opt/aggressive_dead_code_elim_pass.cpp
index 82d7499..b5ce4cc 100644
--- a/source/opt/aggressive_dead_code_elim_pass.cpp
+++ b/source/opt/aggressive_dead_code_elim_pass.cpp
@@ -513,6 +513,26 @@
AddBranch(mergeBlockId, *bi);
for (++bi; (*bi)->id() != mergeBlockId; ++bi) {
}
+
+ auto merge_terminator = (*bi)->terminator();
+ if (merge_terminator->opcode() == SpvOpUnreachable) {
+ // The merge was unreachable. This is undefined behaviour so just
+ // return (or return an undef). Then mark the new return as live.
+ auto func_ret_type_inst = get_def_use_mgr()->GetDef(func->type_id());
+ if (func_ret_type_inst->opcode() == SpvOpTypeVoid) {
+ merge_terminator->SetOpcode(SpvOpReturn);
+ } else {
+ // Find an undef for the return value and make sure it gets kept by
+ // the pass.
+ auto undef_id = Type2Undef(func->type_id());
+ auto undef = get_def_use_mgr()->GetDef(undef_id);
+ live_insts_.Set(undef->unique_id());
+ merge_terminator->SetOpcode(SpvOpReturnValue);
+ merge_terminator->SetInOperands({{SPV_OPERAND_TYPE_ID, {undef_id}}});
+ get_def_use_mgr()->AnalyzeInstUse(merge_terminator);
+ }
+ live_insts_.Set(merge_terminator->unique_id());
+ }
} else {
++bi;
}
diff --git a/test/opt/aggressive_dead_code_elim_test.cpp b/test/opt/aggressive_dead_code_elim_test.cpp
index 8b9b40a..a883fb2 100644
--- a/test/opt/aggressive_dead_code_elim_test.cpp
+++ b/test/opt/aggressive_dead_code_elim_test.cpp
@@ -6210,6 +6210,134 @@
SetAssembleOptions(SPV_TEXT_TO_BINARY_OPTION_PRESERVE_NUMERIC_IDS);
SinglePassRunAndMatch<AggressiveDCEPass>(test, true);
}
+
+TEST_F(AggressiveDCETest, DeadInfiniteLoop) {
+ const std::string test = R"(
+; CHECK: OpSwitch {{%\w+}} {{%\w+}} {{\w+}} {{%\w+}} {{\w+}} [[block:%\w+]]
+; CHECK: [[block]] = OpLabel
+; CHECK-NEXT: OpBranch [[block:%\w+]]
+; CHECK: [[block]] = OpLabel
+; CHECK-NEXT: OpBranch [[block:%\w+]]
+; CHECK: [[block]] = OpLabel
+; CHECK-NEXT: OpReturn
+ OpCapability Shader
+ OpMemoryModel Logical GLSL450
+ OpEntryPoint Fragment %2 "main"
+ OpExecutionMode %2 OriginUpperLeft
+ %6 = OpTypeVoid
+ %7 = OpTypeFunction %6
+ %8 = OpTypeFloat 32
+ %9 = OpTypeVector %8 3
+ %10 = OpTypeFunction %9
+ %11 = OpConstant %8 1
+ %12 = OpConstantComposite %9 %11 %11 %11
+ %13 = OpTypeInt 32 1
+ %32 = OpUndef %13
+ %2 = OpFunction %6 None %7
+ %33 = OpLabel
+ OpBranch %34
+ %34 = OpLabel
+ OpLoopMerge %35 %36 None
+ OpBranch %37
+ %37 = OpLabel
+ %38 = OpFunctionCall %9 %39
+ OpSelectionMerge %40 None
+ OpSwitch %32 %40 14 %41 58 %42
+ %42 = OpLabel
+ OpBranch %43
+ %43 = OpLabel
+ OpLoopMerge %44 %45 None
+ OpBranch %45
+ %45 = OpLabel
+ OpBranch %43
+ %44 = OpLabel
+ OpUnreachable
+ %41 = OpLabel
+ OpBranch %36
+ %40 = OpLabel
+ OpBranch %36
+ %36 = OpLabel
+ OpBranch %34
+ %35 = OpLabel
+ OpReturn
+ OpFunctionEnd
+ %39 = OpFunction %9 None %10
+ %46 = OpLabel
+ OpReturnValue %12
+ OpFunctionEnd
+)";
+
+ SetAssembleOptions(SPV_TEXT_TO_BINARY_OPTION_PRESERVE_NUMERIC_IDS);
+ SinglePassRunAndMatch<AggressiveDCEPass>(test, true);
+}
+
+TEST_F(AggressiveDCETest, DeadInfiniteLoopReturnValue) {
+ const std::string test = R"(
+; CHECK: [[vec3:%\w+]] = OpTypeVector
+; CHECK: [[undef:%\w+]] = OpUndef [[vec3]]
+; CHECK: OpSwitch {{%\w+}} {{%\w+}} {{\w+}} {{%\w+}} {{\w+}} [[block:%\w+]]
+; CHECK: [[block]] = OpLabel
+; CHECK-NEXT: OpBranch [[block:%\w+]]
+; CHECK: [[block]] = OpLabel
+; CHECK-NEXT: OpBranch [[block:%\w+]]
+; CHECK: [[block]] = OpLabel
+; CHECK-NEXT: OpReturnValue [[undef]]
+ OpCapability Shader
+ OpMemoryModel Logical GLSL450
+ OpEntryPoint Fragment %2 "main"
+ OpExecutionMode %2 OriginUpperLeft
+ %6 = OpTypeVoid
+ %7 = OpTypeFunction %6
+ %8 = OpTypeFloat 32
+ %9 = OpTypeVector %8 3
+ %10 = OpTypeFunction %9
+ %11 = OpConstant %8 1
+ %12 = OpConstantComposite %9 %11 %11 %11
+ %13 = OpTypeInt 32 1
+ %32 = OpUndef %13
+ %2 = OpFunction %6 None %7
+ %entry = OpLabel
+ %call = OpFunctionCall %9 %func
+ OpReturn
+ OpFunctionEnd
+ %func = OpFunction %9 None %10
+ %33 = OpLabel
+ OpBranch %34
+ %34 = OpLabel
+ OpLoopMerge %35 %36 None
+ OpBranch %37
+ %37 = OpLabel
+ %38 = OpFunctionCall %9 %39
+ OpSelectionMerge %40 None
+ OpSwitch %32 %40 14 %41 58 %42
+ %42 = OpLabel
+ OpBranch %43
+ %43 = OpLabel
+ OpLoopMerge %44 %45 None
+ OpBranch %45
+ %45 = OpLabel
+ OpBranch %43
+ %44 = OpLabel
+ OpUnreachable
+ %41 = OpLabel
+ OpBranch %36
+ %40 = OpLabel
+ OpBranch %36
+ %36 = OpLabel
+ OpBranch %34
+ %35 = OpLabel
+ OpReturnValue %12
+ OpFunctionEnd
+ %39 = OpFunction %9 None %10
+ %46 = OpLabel
+ OpReturnValue %12
+ OpFunctionEnd
+)";
+
+ SetAssembleOptions(SPV_TEXT_TO_BINARY_OPTION_PRESERVE_NUMERIC_IDS);
+ SinglePassRunAndMatch<AggressiveDCEPass>(test, true);
+}
+
// TODO(greg-lunarg): Add tests to verify handling of these cases:
//
// Check that logical addressing required
