spirv-opt: An off-by-1 error in constant folding #3631
Description
Consider the following SPIR-V
OpCapability Shader
%1 = OpExtInstImport "GLSL.std.450"
OpMemoryModel Logical GLSL450
OpEntryPoint Fragment %4 "main"
OpExecutionMode %4 OriginUpperLeft
OpSource ESSL 310
%2 = OpTypeVoid
%3 = OpTypeFunction %2
%6 = OpTypeFloat 32
%7 = OpTypeVector %6 3
%8 = OpConstant %6 0
%9 = OpConstantComposite %7 %8 %8 %8
%10 = OpTypeVector %6 4
%4 = OpFunction %2 None %3
%5 = OpLabel
%11 = OpCompositeConstruct %10 %9 %8
%12 = OpCompositeExtract %6 %11 3
OpReturn
OpFunctionEnd
An attempt to replace the use of %11 in %12 fails because of the off-by-1 error in
SPIRV-Tools/source/opt/folding_rules.cpp
Lines 1469 to 1479 in b78f4b1
Can be reproduced on b78f4b1.