Don't merge unreachable blocks (#2375)
Fixes #2374
* Block merging no longer merges unreachable blocks into their
successors
* added a test
diff --git a/source/opt/block_merge_util.cpp b/source/opt/block_merge_util.cpp
index 5d6048a..107723d 100644
--- a/source/opt/block_merge_util.cpp
+++ b/source/opt/block_merge_util.cpp
@@ -86,6 +86,11 @@
return false;
}
+ // Don't bother trying to merge unreachable blocks.
+ if (auto dominators = context->GetDominatorAnalysis(block->GetParent())) {
+ if (!dominators->IsReachable(block)) return false;
+ }
+
Instruction* merge_inst = block->GetMergeInst();
const bool pred_is_header = IsHeader(block);
if (pred_is_header && lab_id != merge_inst->GetSingleWordInOperand(0u)) {
diff --git a/test/opt/block_merge_test.cpp b/test/opt/block_merge_test.cpp
index 64ee952..b0f914a 100644
--- a/test/opt/block_merge_test.cpp
+++ b/test/opt/block_merge_test.cpp
@@ -483,6 +483,8 @@
; CHECK-NOT: OpLoopMerge
; CHECK: OpReturn
; CHECK: [[continue:%\w+]] = OpLabel
+; CHECK-NEXT: OpBranch [[block:%\w+]]
+; CHECK: [[block]] = OpLabel
; CHECK-NEXT: OpBranch [[header]]
OpCapability Shader
%1 = OpExtInstImport "GLSL.std.450"
@@ -880,6 +882,47 @@
prefix + suffix_after, true, true);
}
+TEST_F(BlockMergeTest, UnreachableLoop) {
+ const std::string spirv = R"(OpCapability Shader
+%1 = OpExtInstImport "GLSL.std.450"
+OpMemoryModel Logical GLSL450
+OpEntryPoint Fragment %main "main"
+OpExecutionMode %main OriginUpperLeft
+OpSource ESSL 310
+OpName %main "main"
+%void = OpTypeVoid
+%4 = OpTypeFunction %void
+%int = OpTypeInt 32 1
+%_ptr_Function_int = OpTypePointer Function %int
+%bool = OpTypeBool
+%false = OpConstantFalse %bool
+%main = OpFunction %void None %4
+%9 = OpLabel
+OpBranch %10
+%11 = OpLabel
+OpLoopMerge %12 %13 None
+OpBranchConditional %false %13 %14
+%13 = OpLabel
+OpSelectionMerge %15 None
+OpBranchConditional %false %16 %17
+%16 = OpLabel
+OpBranch %15
+%17 = OpLabel
+OpBranch %15
+%15 = OpLabel
+OpBranch %11
+%14 = OpLabel
+OpReturn
+%12 = OpLabel
+OpBranch %10
+%10 = OpLabel
+OpReturn
+OpFunctionEnd
+)";
+
+ SinglePassRunAndCheck<BlockMergePass>(spirv, spirv, true, true);
+}
+
// TODO(greg-lunarg): Add tests to verify handling of these cases:
//
// More complex control flow
