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, 35 insertions, 34 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 3cb1f83..ade937d 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -104,7 +104,7 @@ bool ABIInfo::isPromotableIntegerTypeForABI(QualType Ty) const {
   if (Ty->isPromotableIntegerType())
     return true;
 
-  if (const auto *EIT = Ty->getAs<ExtIntType>())
+  if (const auto *EIT = Ty->getAs<BitIntType>())
     if (EIT->getNumBits() < getContext().getTypeSize(getContext().IntTy))
       return true;
 
@@ -762,7 +762,7 @@ ABIArgInfo DefaultABIInfo::classifyArgumentType(QualType Ty) const {
     Ty = EnumTy->getDecl()->getIntegerType();
 
   ASTContext &Context = getContext();
-  if (const auto *EIT = Ty->getAs<ExtIntType>())
+  if (const auto *EIT = Ty->getAs<BitIntType>())
     if (EIT->getNumBits() >
         Context.getTypeSize(Context.getTargetInfo().hasInt128Type()
                                 ? Context.Int128Ty
@@ -784,7 +784,7 @@ ABIArgInfo DefaultABIInfo::classifyReturnType(QualType RetTy) const {
   if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
     RetTy = EnumTy->getDecl()->getIntegerType();
 
-  if (const auto *EIT = RetTy->getAs<ExtIntType>())
+  if (const auto *EIT = RetTy->getAs<BitIntType>())
     if (EIT->getNumBits() >
         getContext().getTypeSize(getContext().getTargetInfo().hasInt128Type()
                                      ? getContext().Int128Ty
@@ -1008,8 +1008,9 @@ ABIArgInfo PNaClABIInfo::classifyArgumentType(QualType Ty) const {
   } else if (Ty->isFloatingType()) {
     // Floating-point types don't go inreg.
     return ABIArgInfo::getDirect();
-  } else if (const auto *EIT = Ty->getAs<ExtIntType>()) {
-    // Treat extended integers as integers if <=64, otherwise pass indirectly.
+  } else if (const auto *EIT = Ty->getAs<BitIntType>()) {
+    // Treat bit-precise integers as integers if <= 64, otherwise pass
+    // indirectly.
     if (EIT->getNumBits() > 64)
       return getNaturalAlignIndirect(Ty);
     return ABIArgInfo::getDirect();
@@ -1027,8 +1028,8 @@ ABIArgInfo PNaClABIInfo::classifyReturnType(QualType RetTy) const {
   if (isAggregateTypeForABI(RetTy))
     return getNaturalAlignIndirect(RetTy);
 
-  // Treat extended integers as integers if <=64, otherwise pass indirectly.
-  if (const auto *EIT = RetTy->getAs<ExtIntType>()) {
+  // Treat bit-precise integers as integers if <= 64, otherwise pass indirectly.
+  if (const auto *EIT = RetTy->getAs<BitIntType>()) {
     if (EIT->getNumBits() > 64)
       return getNaturalAlignIndirect(RetTy);
     return ABIArgInfo::getDirect();
@@ -1590,7 +1591,7 @@ ABIArgInfo X86_32ABIInfo::classifyReturnType(QualType RetTy,
   if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
     RetTy = EnumTy->getDecl()->getIntegerType();
 
-  if (const auto *EIT = RetTy->getAs<ExtIntType>())
+  if (const auto *EIT = RetTy->getAs<BitIntType>())
     if (EIT->getNumBits() > 64)
       return getIndirectReturnResult(RetTy, State);
 
@@ -1926,7 +1927,7 @@ ABIArgInfo X86_32ABIInfo::classifyArgumentType(QualType Ty,
     return ABIArgInfo::getExtend(Ty);
   }
 
-  if (const auto * EIT = Ty->getAs<ExtIntType>()) {
+  if (const auto *EIT = Ty->getAs<BitIntType>()) {
     if (EIT->getNumBits() <= 64) {
       if (InReg)
         return ABIArgInfo::getDirectInReg();
@@ -3009,7 +3010,7 @@ void X86_64ABIInfo::classify(QualType Ty, uint64_t OffsetBase,
     return;
   }
 
-  if (const auto *EITy = Ty->getAs<ExtIntType>()) {
+  if (const auto *EITy = Ty->getAs<BitIntType>()) {
     if (EITy->getNumBits() <= 64)
       Current = Integer;
     else if (EITy->getNumBits() <= 128)
@@ -3200,7 +3201,7 @@ ABIArgInfo X86_64ABIInfo::getIndirectReturnResult(QualType Ty) const {
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
       Ty = EnumTy->getDecl()->getIntegerType();
 
-    if (Ty->isExtIntType())
+    if (Ty->isBitIntType())
       return getNaturalAlignIndirect(Ty);
 
     return (isPromotableIntegerTypeForABI(Ty) ? ABIArgInfo::getExtend(Ty)
@@ -3237,7 +3238,7 @@ ABIArgInfo X86_64ABIInfo::getIndirectResult(QualType Ty,
   // but this code would be much safer if we could mark the argument with
   // 'onstack'. See PR12193.
   if (!isAggregateTypeForABI(Ty) && !IsIllegalVectorType(Ty) &&
-      !Ty->isExtIntType()) {
+      !Ty->isBitIntType()) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
       Ty = EnumTy->getDecl()->getIntegerType();
@@ -4357,12 +4358,12 @@ ABIArgInfo WinX86_64ABIInfo::classify(QualType Ty, unsigned &FreeSSERegs,
     }
   }
 
-  if (Ty->isExtIntType()) {
+  if (Ty->isBitIntType()) {
     // MS x64 ABI requirement: "Any argument that doesn't fit in 8 bytes, or is
     // not 1, 2, 4, or 8 bytes, must be passed by reference."
-    // However, non-power-of-two _ExtInts will be passed as 1,2,4 or 8 bytes
-    // anyway as long is it fits in them, so we don't have to check the power of
-    // 2.
+    // However, non-power-of-two bit-precise integers will be passed as 1, 2, 4,
+    // or 8 bytes anyway as long is it fits in them, so we don't have to check
+    // the power of 2.
     if (Width <= 64)
       return ABIArgInfo::getDirect();
     return ABIArgInfo::getIndirect(Align, /*ByVal=*/false);
@@ -5069,7 +5070,7 @@ PPC64_SVR4_ABIInfo::isPromotableTypeForABI(QualType Ty) const {
       break;
     }
 
-  if (const auto *EIT = Ty->getAs<ExtIntType>())
+  if (const auto *EIT = Ty->getAs<BitIntType>())
     if (EIT->getNumBits() < 64)
       return true;
 
@@ -5294,7 +5295,7 @@ PPC64_SVR4_ABIInfo::classifyArgumentType(QualType Ty) const {
     }
   }
 
-  if (const auto *EIT = Ty->getAs<ExtIntType>())
+  if (const auto *EIT = Ty->getAs<BitIntType>())
     if (EIT->getNumBits() > 128)
       return getNaturalAlignIndirect(Ty, /*ByVal=*/true);
 
@@ -5370,7 +5371,7 @@ PPC64_SVR4_ABIInfo::classifyReturnType(QualType RetTy) const {
     }
   }
 
-  if (const auto *EIT = RetTy->getAs<ExtIntType>())
+  if (const auto *EIT = RetTy->getAs<BitIntType>())
     if (EIT->getNumBits() > 128)
       return getNaturalAlignIndirect(RetTy, /*ByVal=*/false);
 
@@ -5722,7 +5723,7 @@ AArch64ABIInfo::classifyArgumentType(QualType Ty, bool IsVariadic,
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
       Ty = EnumTy->getDecl()->getIntegerType();
 
-    if (const auto *EIT = Ty->getAs<ExtIntType>())
+    if (const auto *EIT = Ty->getAs<BitIntType>())
       if (EIT->getNumBits() > 128)
         return getNaturalAlignIndirect(Ty);
 
@@ -5824,7 +5825,7 @@ ABIArgInfo AArch64ABIInfo::classifyReturnType(QualType RetTy,
     if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
       RetTy = EnumTy->getDecl()->getIntegerType();
 
-    if (const auto *EIT = RetTy->getAs<ExtIntType>())
+    if (const auto *EIT = RetTy->getAs<BitIntType>())
       if (EIT->getNumBits() > 128)
         return getNaturalAlignIndirect(RetTy);
 
@@ -6566,7 +6567,7 @@ ABIArgInfo ARMABIInfo::classifyArgumentType(QualType Ty, bool isVariadic,
       Ty = EnumTy->getDecl()->getIntegerType();
     }
 
-    if (const auto *EIT = Ty->getAs<ExtIntType>())
+    if (const auto *EIT = Ty->getAs<BitIntType>())
       if (EIT->getNumBits() > 64)
         return getNaturalAlignIndirect(Ty, /*ByVal=*/true);
 
@@ -6768,7 +6769,7 @@ ABIArgInfo ARMABIInfo::classifyReturnType(QualType RetTy, bool isVariadic,
     if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
       RetTy = EnumTy->getDecl()->getIntegerType();
 
-    if (const auto *EIT = RetTy->getAs<ExtIntType>())
+    if (const auto *EIT = RetTy->getAs<BitIntType>())
       if (EIT->getNumBits() > 64)
         return getNaturalAlignIndirect(RetTy, /*ByVal=*/false);
 
@@ -7105,7 +7106,7 @@ bool NVPTXABIInfo::isUnsupportedType(QualType T) const {
       (T->isFloat128Type() ||
        (T->isRealFloatingType() && Context.getTypeSize(T) == 128)))
     return true;
-  if (const auto *EIT = T->getAs<ExtIntType>())
+  if (const auto *EIT = T->getAs<BitIntType>())
     return EIT->getNumBits() >
            (Context.getTargetInfo().hasInt128Type() ? 128U : 64U);
   if (!Context.getTargetInfo().hasInt128Type() && T->isIntegerType() &&
@@ -7182,7 +7183,7 @@ ABIArgInfo NVPTXABIInfo::classifyArgumentType(QualType Ty) const {
     return getNaturalAlignIndirect(Ty, /* byval */ true);
   }
 
-  if (const auto *EIT = Ty->getAs<ExtIntType>()) {
+  if (const auto *EIT = Ty->getAs<BitIntType>()) {
     if ((EIT->getNumBits() > 128) ||
         (!getContext().getTargetInfo().hasInt128Type() &&
          EIT->getNumBits() > 64))
@@ -7396,7 +7397,7 @@ bool SystemZABIInfo::isPromotableIntegerTypeForABI(QualType Ty) const {
   if (ABIInfo::isPromotableIntegerTypeForABI(Ty))
     return true;
 
-  if (const auto *EIT = Ty->getAs<ExtIntType>())
+  if (const auto *EIT = Ty->getAs<BitIntType>())
     if (EIT->getNumBits() < 64)
       return true;
 
@@ -7999,7 +8000,7 @@ MipsABIInfo::classifyArgumentType(QualType Ty, uint64_t &Offset) const {
     Ty = EnumTy->getDecl()->getIntegerType();
 
   // Make sure we pass indirectly things that are too large.
-  if (const auto *EIT = Ty->getAs<ExtIntType>())
+  if (const auto *EIT = Ty->getAs<BitIntType>())
     if (EIT->getNumBits() > 128 ||
         (EIT->getNumBits() > 64 &&
          !getContext().getTargetInfo().hasInt128Type()))
@@ -8090,7 +8091,7 @@ ABIArgInfo MipsABIInfo::classifyReturnType(QualType RetTy) const {
     RetTy = EnumTy->getDecl()->getIntegerType();
 
   // Make sure we pass indirectly things that are too large.
-  if (const auto *EIT = RetTy->getAs<ExtIntType>())
+  if (const auto *EIT = RetTy->getAs<BitIntType>())
     if (EIT->getNumBits() > 128 ||
         (EIT->getNumBits() > 64 &&
          !getContext().getTargetInfo().hasInt128Type()))
@@ -8465,7 +8466,7 @@ ABIArgInfo HexagonABIInfo::classifyArgumentType(QualType Ty,
     if (Size <= 64)
       HexagonAdjustRegsLeft(Size, RegsLeft);
 
-    if (Size > 64 && Ty->isExtIntType())
+    if (Size > 64 && Ty->isBitIntType())
       return getNaturalAlignIndirect(Ty, /*ByVal=*/true);
 
     return isPromotableIntegerTypeForABI(Ty) ? ABIArgInfo::getExtend(Ty)
@@ -8521,7 +8522,7 @@ ABIArgInfo HexagonABIInfo::classifyReturnType(QualType RetTy) const {
     if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
       RetTy = EnumTy->getDecl()->getIntegerType();
 
-    if (Size > 64 && RetTy->isExtIntType())
+    if (Size > 64 && RetTy->isBitIntType())
       return getNaturalAlignIndirect(RetTy, /*ByVal=*/false);
 
     return isPromotableIntegerTypeForABI(RetTy) ? ABIArgInfo::getExtend(RetTy)
@@ -8892,7 +8893,7 @@ ABIArgInfo LanaiABIInfo::classifyArgumentType(QualType Ty,
   bool InReg = shouldUseInReg(Ty, State);
 
   // Don't pass >64 bit integers in registers.
-  if (const auto *EIT = Ty->getAs<ExtIntType>())
+  if (const auto *EIT = Ty->getAs<BitIntType>())
     if (EIT->getNumBits() > 64)
       return getIndirectResult(Ty, /*ByVal=*/true, State);
 
@@ -9624,7 +9625,7 @@ SparcV9ABIInfo::classifyType(QualType Ty, unsigned SizeLimit) const {
   if (Size < 64 && Ty->isIntegerType())
     return ABIArgInfo::getExtend(Ty);
 
-  if (const auto *EIT = Ty->getAs<ExtIntType>())
+  if (const auto *EIT = Ty->getAs<BitIntType>())
     if (EIT->getNumBits() < 64)
       return ABIArgInfo::getExtend(Ty);
 
@@ -9878,7 +9879,7 @@ ABIArgInfo ARCABIInfo::classifyArgumentType(QualType Ty,
         ABIArgInfo::getDirect(Result, 0, nullptr, false);
   }
 
-  if (const auto *EIT = Ty->getAs<ExtIntType>())
+  if (const auto *EIT = Ty->getAs<BitIntType>())
     if (EIT->getNumBits() > 64)
       return getIndirectByValue(Ty);
 
@@ -10961,7 +10962,7 @@ ABIArgInfo RISCVABIInfo::classifyArgumentType(QualType Ty, bool IsFixed,
       return extendType(Ty);
     }
 
-    if (const auto *EIT = Ty->getAs<ExtIntType>()) {
+    if (const auto *EIT = Ty->getAs<BitIntType>()) {
       if (EIT->getNumBits() < XLen && !MustUseStack)
         return extendType(Ty);
       if (EIT->getNumBits() > 128 ||