[clang] [clang] Bind the __builtin_bit_cast operand as std::bit_cast binds its parameter (PR #231830)

[Hubert Tong via cfe-commits]

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@@ -2658,6 +2658,8 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     Address Addr =
         SourceLVal.getAddress().withElementType(CGF.ConvertTypeForMem(DestTy));
     LValue DestLV = CGF.MakeAddrLValue(Addr, DestTy);
+    if (SourceLVal.isVolatileQualified())
+      DestLV.getQuals().addVolatile();
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hubert-reinterpretcast wrote:

> The standard specification for std::bit_cast doesn't actually say what happens if the operand is volatile.

That seems to be a real problem because there really isn't supposed to be an lvalue-to-rvalue conversion of the bound input glvalue, but trying to apply `volatile` semantics on the object representation would result in multiple volatile accesses. I'll report the issue tomorrow or later this week.

https://github.com/llvm/llvm-project/pull/231830