inliner generates invalid OpLabel if callee has single return in block that does not appear last #755
Description
Example code:
OpCapability Shader
%1 = OpExtInstImport "GLSL.std.450"
OpMemoryModel Logical GLSL450
OpEntryPoint Vertex %main "main"
OpSource GLSL 450
OpName %main "main"
OpName %foo_ "foo("
%void = OpTypeVoid
%3 = OpTypeFunction %void
%bool = OpTypeBool
%true = OpConstantTrue %bool
%main = OpFunction %void None %3
%5 = OpLabel
%12 = OpFunctionCall %void %foo_
OpReturn
OpFunctionEnd
%foo_ = OpFunction %void None %3
%7 = OpLabel
OpSelectionMerge %11 None
OpBranchConditional %true %10 %11
%11 = OpLabel
OpReturn ; This causes returnLabelId to be non-zero, but earlyReturn is false.
%10 = OpLabel
OpBranch %11
OpFunctionEnd
It's generated from this vertex shader, but where I reorder, in the SPIR-V assembly, the last two basic blocks of the "foo" function:
#version 450
void foo() {
if (true) {
}
}
void main() {
foo();
}
When running spirv-opt with inline-entry-points-exhaustive:
- returnLabelId is non-zero since we encountered an OpReturn well before the OpFunctionEnd
- but earlyReturn is false
- but at OpFunctionEnd we generate "continue target" with OpLabel for result id singleTripLoopContinueId. But that is still zero.
- this causes a new instruction with OpLabel opcode, but zero result Id, and generates a 1-word OpLabel instruction, which is invalid.
Likely remedy is to guard the codegen of continue target block by earlyReturn. Still have to create the block with label Id returnLabelId.