[llvm] [SPIR-V] Fix an undefined behaviour in the SPIRV emit-intrinsics pass (PR #123620)

[Nathan Gauër via llvm-commits]

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@@ -2475,8 +2475,10 @@ void SPIRVEmitIntrinsics::parseFunDeclarations(Module &M) {
     if (DemangledName.empty())
       continue;
     // allow only OpGroupAsyncCopy use case at the moment
-    auto [Grp, Opcode, ExtNo] =
-        SPIRV::mapBuiltinToOpcode(DemangledName, InstrSet);
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Keenuts wrote:

Should this variable be removed from the class?

https://github.com/llvm/llvm-project/pull/123620