[clang] [compiler-rt] [clang][UBSan] Add implicit conversion check for bitfields (PR #75481)

[John McCall via cfe-commits]

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@@ -1239,6 +1257,228 @@ void ScalarExprEmitter::EmitIntegerSignChangeCheck(Value *Src, QualType SrcType,
                 {Src, Dst});
 }
 
+// Should be called within CodeGenFunction::SanitizerScope RAII scope.
+// Returns 'i1 false' when the truncation Src -> Dst was lossy.
+static std::pair<ScalarExprEmitter::ImplicitConversionCheckKind,
+                 std::pair<llvm::Value *, SanitizerMask>>
+EmitBitfieldTruncationCheckHelper(Value *Src, QualType SrcType, Value *Dst,
+                                  QualType DstType, CGBuilderTy &Builder) {
+
+  llvm::Type *SrcTy = Src->getType();
+  llvm::Type *DstTy = Dst->getType();
+  (void)SrcTy; // Only used in assert()
+  (void)DstTy; // Only used in assert()
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rjmccall wrote:

Then you should surround these variables with `#ifndef NDEBUG`.  But mostly you don't need to do this; `CreateIntCast` will assert this for you.

https://github.com/llvm/llvm-project/pull/75481