Introduce _BitInt, deprecate _ExtInt

WG14 adopted the _ExtInt feature from Clang for C23, but renamed the
type to be _BitInt. This patch does the vast majority of the work to
rename _ExtInt to _BitInt, which accounts for most of its size. The new
type is exposed in older C modes and all C++ modes as a conforming
extension. However, there are functional changes worth calling out:

* Deprecates _ExtInt with a fix-it to help users migrate to _BitInt.
* Updates the mangling for the type.
* Updates the documentation and adds a release note to warn users what
is going on.
* Adds new diagnostics for use of _BitInt to call out when it's used as
a Clang extension or as a pre-C23 compatibility concern.
* Adds new tests for the new diagnostic behaviors.

I want to call out the ABI break specifically. We do not believe that
this break will cause a significant imposition for early adopters of
the feature, and so this is being done as a full break. If it turns out
there are critical uses where recompilation is not an option for some
reason, we can consider using ABI tags to ease the transition.

1 files changed, 13 insertions, 13 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 33e2b3b..fc3886e 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -325,17 +325,17 @@ static bool SemaBuiltinOverflow(Sema &S, CallExpr *TheCall,
     }
   }
 
-  // Disallow signed ExtIntType args larger than 128 bits to mul function until
-  // we improve backend support.
+  // Disallow signed bit-precise integer args larger than 128 bits to mul
+  // function until we improve backend support.
   if (BuiltinID == Builtin::BI__builtin_mul_overflow) {
     for (unsigned I = 0; I < 3; ++I) {
       const auto Arg = TheCall->getArg(I);
       // Third argument will be a pointer.
       auto Ty = I < 2 ? Arg->getType() : Arg->getType()->getPointeeType();
-      if (Ty->isExtIntType() && Ty->isSignedIntegerType() &&
+      if (Ty->isBitIntType() && Ty->isSignedIntegerType() &&
           S.getASTContext().getIntWidth(Ty) > 128)
         return S.Diag(Arg->getBeginLoc(),
-                      diag::err_overflow_builtin_ext_int_max_size)
+                      diag::err_overflow_builtin_bit_int_max_size)
                << 128;
     }
   }
@@ -5819,8 +5819,8 @@ ExprResult Sema::BuildAtomicExpr(SourceRange CallRange, SourceRange ExprRange,
                 ? 0
                 : 1);
 
-  if (ValType->isExtIntType()) {
-    Diag(Ptr->getExprLoc(), diag::err_atomic_builtin_ext_int_prohibit);
+  if (ValType->isBitIntType()) {
+    Diag(Ptr->getExprLoc(), diag::err_atomic_builtin_bit_int_prohibit);
     return ExprError();
   }
 
@@ -6217,11 +6217,11 @@ Sema::SemaBuiltinAtomicOverloaded(ExprResult TheCallResult) {
   // gracefully.
   TheCall->setType(ResultType);
 
-  // Prohibit use of _ExtInt with atomic builtins.
-  // The arguments would have already been converted to the first argument's
-  // type, so only need to check the first argument.
-  const auto *ExtIntValType = ValType->getAs<ExtIntType>();
-  if (ExtIntValType && !llvm::isPowerOf2_64(ExtIntValType->getNumBits())) {
+  // Prohibit problematic uses of bit-precise integer types with atomic
+  // builtins. The arguments would have already been converted to the first
+  // argument's type, so only need to check the first argument.
+  const auto *BitIntValType = ValType->getAs<BitIntType>();
+  if (BitIntValType && !llvm::isPowerOf2_64(BitIntValType->getNumBits())) {
     Diag(FirstArg->getExprLoc(), diag::err_atomic_builtin_ext_int_size);
     return ExprError();
   }
@@ -11249,7 +11249,7 @@ struct IntRange {
                         false/*NonNegative*/);
     }
 
-    if (const auto *EIT = dyn_cast<ExtIntType>(T))
+    if (const auto *EIT = dyn_cast<BitIntType>(T))
       return IntRange(EIT->getNumBits(), EIT->isUnsigned());
 
     const BuiltinType *BT = cast<BuiltinType>(T);
@@ -11275,7 +11275,7 @@ struct IntRange {
     if (const EnumType *ET = dyn_cast<EnumType>(T))
       T = C.getCanonicalType(ET->getDecl()->getIntegerType()).getTypePtr();
 
-    if (const auto *EIT = dyn_cast<ExtIntType>(T))
+    if (const auto *EIT = dyn_cast<BitIntType>(T))
       return IntRange(EIT->getNumBits(), EIT->isUnsigned());
 
     const BuiltinType *BT = cast<BuiltinType>(T);