[C++2a] Add __builtin_bit_cast, used to implement std::bit_cast
This commit adds a new builtin, __builtin_bit_cast(T, v), which performs a
bit_cast from a value v to a type T. This expression can be evaluated at
compile time under specific circumstances.
The compile time evaluation currently doesn't support bit-fields, but I'm
planning on fixing this in a follow up (some of the logic for figuring this out
is in CodeGen). I'm also planning follow-ups for supporting some more esoteric
types that the constexpr evaluator supports, as well as extending
__builtin_memcpy constexpr evaluation to use the same infrastructure.
rdar://44987528
Differential revision: https://reviews.llvm.org/D62825
llvm-svn: 364954
diff --git a/clang/lib/CodeGen/CGExprComplex.cpp b/clang/lib/CodeGen/CGExprComplex.cpp
index 4906b63..6a5fb45 100644
--- a/clang/lib/CodeGen/CGExprComplex.cpp
+++ b/clang/lib/CodeGen/CGExprComplex.cpp
@@ -464,6 +464,15 @@
return EmitLoadOfLValue(CGF.MakeAddrLValue(V, DestTy), Op->getExprLoc());
}
+ case CK_LValueToRValueBitCast: {
+ LValue SourceLVal = CGF.EmitLValue(Op);
+ Address Addr = Builder.CreateElementBitCast(SourceLVal.getAddress(),
+ CGF.ConvertTypeForMem(DestTy));
+ LValue DestLV = CGF.MakeAddrLValue(Addr, DestTy);
+ DestLV.setTBAAInfo(TBAAAccessInfo::getMayAliasInfo());
+ return EmitLoadOfLValue(DestLV, Op->getExprLoc());
+ }
+
case CK_BitCast:
case CK_BaseToDerived:
case CK_DerivedToBase: