[clang] [clang][CodeGen][UBSan] Fixing shift-exponent generation for _BitInt (PR #80515)

[Adam Magier via cfe-commits]

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@@ -4121,6 +4121,13 @@ Value *ScalarExprEmitter::GetWidthMinusOneValue(Value* LHS,Value* RHS) {
     Ty = cast<llvm::IntegerType>(VT->getElementType());
   else
     Ty = cast<llvm::IntegerType>(LHS->getType());
+  // Testing with small _BitInt types has shown that Ty->getBitwidth() - 1
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AdamMagierFOSS wrote:

I've renamed the function to be more accurate, but to keep a consistent style with the surrounding code I've not put a formal function description and instead kept the explanatory comment (though rewriting it to not include mentions of _BitInt).

https://github.com/llvm/llvm-project/pull/80515