[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

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/AST/StmtProfile.cpp b/clang/lib/AST/StmtProfile.cpp
index c5da5bfda9c..f92c3dc60ba 100644
--- a/clang/lib/AST/StmtProfile.cpp
+++ b/clang/lib/AST/StmtProfile.cpp
@@ -1569,6 +1569,11 @@ void StmtProfiler::VisitCXXConstCastExpr(const CXXConstCastExpr *S) {
   VisitCXXNamedCastExpr(S);
 }
 
+void StmtProfiler::VisitBuiltinBitCastExpr(const BuiltinBitCastExpr *S) {
+  VisitExpr(S);
+  VisitType(S->getTypeInfoAsWritten()->getType());
+}
+
 void StmtProfiler::VisitUserDefinedLiteral(const UserDefinedLiteral *S) {
   VisitCallExpr(S);
 }