[Clang] Implement constexpr support for __builtin_popcountg (#84318)

clang/docs/LanguageExtensions.rst

@@ -5378,6 +5378,7 @@ The following builtin intrinsics can be used in constant expressions:
 * ``__builtin_popcount``
 * ``__builtin_popcountl``
 * ``__builtin_popcountll``
+* ``__builtin_popcountg``
 * ``__builtin_rotateleft8``
 * ``__builtin_rotateleft16``
 * ``__builtin_rotateleft32``

clang/docs/ReleaseNotes.rst

@@ -157,6 +157,11 @@ Non-comprehensive list of changes in this release
 - ``__builtin_addc``, ``__builtin_subc``, and the other sizes of those
   builtins are now constexpr and may be used in constant expressions.
 
+- Added ``__builtin_popcountg`` as a type-generic alternative to
+  ``__builtin_popcount{,l,ll}`` with support for any unsigned integer type. Like
+  the previous builtins, this new builtin is constexpr and may be used in
+  constant expressions.
+
 New Compiler Flags
 ------------------
 

clang/include/clang/Basic/Builtins.td

@@ -706,7 +706,7 @@ def Popcount : Builtin, BitInt_Long_LongLongTemplate {
 
 def Popcountg : Builtin {
   let Spellings = ["__builtin_popcountg"];
-  let Attributes = [NoThrow, Const, CustomTypeChecking];
+  let Attributes = [NoThrow, Const, Constexpr, CustomTypeChecking];
   let Prototype = "int(...)";
 }
 

clang/lib/AST/ExprConstant.cpp

@@ -12483,6 +12483,7 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
   case Builtin::BI__builtin_popcount:
   case Builtin::BI__builtin_popcountl:
   case Builtin::BI__builtin_popcountll:
+  case Builtin::BI__builtin_popcountg:
   case Builtin::BI__popcnt16: // Microsoft variants of popcount
   case Builtin::BI__popcnt:
   case Builtin::BI__popcnt64: {

clang/test/Sema/constant-builtins-2.c

@@ -237,6 +237,13 @@ char popcount7[__builtin_popcountl(~0L) == BITSIZE(long) ? 1 : -1];
 char popcount8[__builtin_popcountll(0LL) == 0 ? 1 : -1];
 char popcount9[__builtin_popcountll(0xF0F0LL) == 8 ? 1 : -1];
 char popcount10[__builtin_popcountll(~0LL) == BITSIZE(long long) ? 1 : -1];
+char popcount11[__builtin_popcountg(0U) == 0 ? 1 : -1];
+char popcount12[__builtin_popcountg(0xF0F0U) == 8 ? 1 : -1];
+char popcount13[__builtin_popcountg(~0U) == BITSIZE(int) ? 1 : -1];
+char popcount14[__builtin_popcountg(~0UL) == BITSIZE(long) ? 1 : -1];
+char popcount15[__builtin_popcountg(~0ULL) == BITSIZE(long long) ? 1 : -1];
+char popcount16[__builtin_popcountg(~(unsigned __int128)0) == BITSIZE(__int128) ? 1 : -1];
+char popcount17[__builtin_popcountg(~(unsigned _BitInt(128))0) == BITSIZE(_BitInt(128)) ? 1 : -1];
 
 char parity1[__builtin_parity(0) == 0 ? 1 : -1];
 char parity2[__builtin_parity(0xb821) == 0 ? 1 : -1];