spirv-diff crashing with OpString

[spencer-lunarg]

Take the following, duplicate it and go spirv-diff a.spv b.spv and it will crash with

/source/diff/diff.cpp:2734: opt::Instruction spvtools::diff::(anonymous namespace)::Differ::ToMappedSrcIds(const opt::Instruction &): Assertion `id_map_.IsDstMapped(operand.AsId())' failed.

               OpCapability Shader
               OpExtension "SPV_KHR_non_semantic_info"
          %1 = OpExtInstImport "GLSL.std.450"
         %12 = OpExtInstImport "NonSemantic.DebugPrintf"
               OpMemoryModel Logical GLSL450
               OpEntryPoint GLCompute %main "main"
               OpExecutionMode %main LocalSize 1 1 1
         %10 = OpString "unsigned == %u"
               OpSource GLSL 450
               OpSourceExtension "GL_EXT_debug_printf"
               OpName %main "main"
               OpName %foo "foo"
       %void = OpTypeVoid
          %3 = OpTypeFunction %void
       %uint = OpTypeInt 32 0
%_ptr_Function_uint = OpTypePointer Function %uint
   %uint_127 = OpConstant %uint 127
       %main = OpFunction %void None %3
          %5 = OpLabel
        %foo = OpVariable %_ptr_Function_uint Function
               OpStore %foo %uint_127
         %11 = OpLoad %uint %foo
         %13 = OpExtInst %void %12 1 %10 %11
               OpReturn
               OpFunctionEnd

cc @ShabbyX (might not get time to soon, but wanted to report it)

[ShabbyX]

Thanks for the report. spirv-diff is not creating a mapping for %10 which is only a parameter of OpExtInst. Normally, its expectation is that the parameters are already matched for other reasons (like %11 is matched because of OpLoad). In this case, it's just a string, so my assumption there was wrong. Should be easy to fix hopefully, at least assuming OpExtInst is the only one that's dealing with these not-really-otherwise-used values.

[ShabbyX]

Actually the crash itself was due something more trivial, the map of id->instruction was not being populated for debug instructions. This fixes the crash: #5988

The OpString instructions are still not correctly matched with that fix, but at least there is no crash.