spirv-opt module builder injects extra OpLine instructions that don't exist on the input #4029
Description
This is a consequence of #3951
This breaks some line number attribution in Tint, and breaks one of its tests.
Here's the sample SPIR-V assembly:
OpCapability Shader
OpMemoryModel Logical Simple
OpEntryPoint GLCompute %2 "main"
OpExecutionMode %2 LocalSize 1 1 1
%15 = OpString "myfile"
%void = OpTypeVoid
%4 = OpTypeFunction %void
OpLine %15 42 53
%uint = OpTypeInt 32 0
%60 = OpConstantNull %uint
OpNoLine
%2 = OpFunction %void None %4
%1 = OpLabel
OpReturn
OpFunctionEnd
The test checks to see that %1 is instruction number 13 (start counting from 1).
That worked until #3951 was merged, and now it is reported as instruction number 14.
The Tint cod uses module->ForEachInst to walk the module. To help debug the issue I added a print to see the opcode for each instruction that is visited. I get this output:
[ RUN ] SpvParserTest.Impl_Source_WithOpLine_WithOpNoLine
inst 17
inst 14
inst 15
inst 16
inst 7
inst 19
inst 33
inst 8
inst 21
inst 8 ; <<<<< This was an OpLine injected by the change in #3951
inst 46
inst 317
inst 54
inst 248
inst 253
inst 56
Basically, the module no longer accurately represents the input module.