spirv-opt: CCP pass still changes the module and returns SuccessWithoutChange

[Vasniktel]

The following shader

               OpCapability Shader
          %1 = OpExtInstImport "GLSL.std.450"
               OpMemoryModel Logical GLSL450
               OpEntryPoint Fragment %4 "main"
               OpExecutionMode %4 OriginUpperLeft
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %8 = OpTypeFloat 32
         %12 = OpTypeVector %8 3
         %87 = OpTypeInt 32 0
         %88 = OpConstant %87 0
        %153 = OpTypeBool
        %154 = OpTypeVector %153 3
        %398 = OpConstant %8 0
        %399 = OpConstantComposite %12 %398 %398 %398
        %533 = OpConstant %8 0.300000012
        %534 = OpConstantComposite %12 %533 %533 %533
          %4 = OpFunction %2 None %3
          %5 = OpLabel
               OpBranch %2209
       %2209 = OpLabel
       %3155 = OpPhi %12 %399 %5 %534 %2272
       %3246 = OpFOrdLessThan %154 %3155 %534
       %3247 = OpAll %153 %3246
               OpLoopMerge %2275 %2272 None
               OpBranchConditional %3247 %2272 %2275
       %2272 = OpLabel
               OpBranch %2209
       %2275 = OpLabel
        %535 = OpExtInst %12 %1 FMix %399 %3155 %534
               OpReturn
               OpFunctionEnd

produces an error

spirv-opt: /home/vasniktel/gsoc/spirv-repo/source/opt/optimizer.cpp:592: bool spvtools::Optimizer::Run(const uint32_t *, const size_t, std::vector<uint32_t> *, const spv_optimizer_options) const: Assertion `optimized_binary_with_nop.size() == original_binary_size && "Binary size unexpectedly changed despite the optimizer saying " "there was no change"' failed.

when executed with spirv-opt <compiled binary> -o out.spv --ccp --validate-after-all.

Can be reproduced on 4dd1223.

The situation is similar to #3636 except that the created constant is not returned and instead used internally by the folder. In this particular example, the folder creates a constant 1 and 1 - %534 (this is required by the OpFMix instruction).

[Vasniktel]

@dnovillo for info.

[dnovillo]

Thanks. I'll try to work on it this week.

[dnovillo]

@Vasniktel apologies for the delay. It is unlikely that I will have time to work on this in the next couple of weeks.

[Vasniktel]

@dnovillo, no worries :)