[clang] [compiler-rt] [ubsan] Display correct runtime messages for negative _BitInt (PR #96240)

[Adam Magier via llvm-commits]

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@@ -3324,6 +3359,20 @@ llvm::Constant *CodeGenFunction::EmitCheckTypeDescriptor(QualType T) {
       DiagnosticsEngine::ak_qualtype, (intptr_t)T.getAsOpaquePtr(), StringRef(),
       StringRef(), std::nullopt, Buffer, std::nullopt);
 
+  if (IsBitInt) {
+    // The Structure is: 0 to end the string, 32 bit unsigned integer in target
+    // endianness, zero.
+    char S[6] = {'\0', '\0', '\0', '\0', '\0', '\0'};
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AdamMagierFOSS wrote:

Probably a bit too late to the party and I struggle with following discussion history on GitHub, but what was the reasoning behind storing the bit width encoded in the name of the type versus parsing out the bit width from the name of the type itself in the runtime (e.g. parsing out the value 37 from '_BitInt(37)' instead of extracting the literal 37 from '_BitInt(37)\x00\x25\x00\x00\x00' )? I would imagine that the former would be easier since there wouldn't be any platform dependence when traversing the string, and I don't think it would incur too much of an extra performance hit (the solution might look a bit kludgey though)

https://github.com/llvm/llvm-project/pull/96240