[clang] Implement constexpr support for __builtin_{clzg,ctzg} (#86577)

Fixes #86549.

Author: overmighty

clang/docs/LanguageExtensions.rst

@@ -5420,10 +5420,12 @@ The following builtin intrinsics can be used in constant expressions:
 * ``__builtin_clzl``
 * ``__builtin_clzll``
 * ``__builtin_clzs``
+* ``__builtin_clzg``
 * ``__builtin_ctz``
 * ``__builtin_ctzl``
 * ``__builtin_ctzll``
 * ``__builtin_ctzs``
+* ``__builtin_ctzg``
 * ``__builtin_ffs``
 * ``__builtin_ffsl``
 * ``__builtin_ffsll``

clang/docs/ReleaseNotes.rst

@@ -188,6 +188,11 @@ Non-comprehensive list of changes in this release
 
 - Lambda expressions are now accepted in C++03 mode as an extension.
 
+- Added ``__builtin_clzg`` and ``__builtin_ctzg`` as type-generic alternatives
+  to ``__builtin_clz{,s,l,ll}`` and ``__builtin_ctz{,s,l,ll}`` respectively,
+  with support for any unsigned integer type. Like the previous builtins, these
+  new builtins are constexpr and may be used in constant expressions.
+
 New Compiler Flags
 ------------------
 

clang/include/clang/Basic/Builtins.td

@@ -678,7 +678,7 @@ def Clz : Builtin, BitShort_Int_Long_LongLongTemplate {
 
 def Clzg : Builtin {
   let Spellings = ["__builtin_clzg"];
-  let Attributes = [NoThrow, Const, CustomTypeChecking];
+  let Attributes = [NoThrow, Const, Constexpr, CustomTypeChecking];
   let Prototype = "int(...)";
 }
 
@@ -690,7 +690,7 @@ def Ctz : Builtin, BitShort_Int_Long_LongLongTemplate {
 
 def Ctzg : Builtin {
   let Spellings = ["__builtin_ctzg"];
-  let Attributes = [NoThrow, Const, CustomTypeChecking];
+  let Attributes = [NoThrow, Const, Constexpr, CustomTypeChecking];
   let Prototype = "int(...)";
 }
 

clang/lib/AST/ExprConstant.cpp

@@ -12353,21 +12353,31 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
   case Builtin::BI__builtin_clzl:
   case Builtin::BI__builtin_clzll:
   case Builtin::BI__builtin_clzs:
+  case Builtin::BI__builtin_clzg:
   case Builtin::BI__lzcnt16: // Microsoft variants of count leading-zeroes
   case Builtin::BI__lzcnt:
   case Builtin::BI__lzcnt64: {
     APSInt Val;
     if (!EvaluateInteger(E->getArg(0), Val, Info))
       return false;
 
-    // When the argument is 0, the result of GCC builtins is undefined, whereas
-    // for Microsoft intrinsics, the result is the bit-width of the argument.
-    bool ZeroIsUndefined = BuiltinOp != Builtin::BI__lzcnt16 &&
-                           BuiltinOp != Builtin::BI__lzcnt &&
-                           BuiltinOp != Builtin::BI__lzcnt64;
+    if (!Val) {
+      if (BuiltinOp == Builtin::BI__builtin_clzg && E->getNumArgs() > 1) {
+        if (!EvaluateInteger(E->getArg(1), Val, Info))
+          return false;
+        return Success(Val, E);
+      }
 
-    if (ZeroIsUndefined && !Val)
-      return Error(E);
+      // When the argument is 0, the result of GCC builtins is undefined,
+      // whereas for Microsoft intrinsics, the result is the bit-width of the
+      // argument.
+      bool ZeroIsUndefined = BuiltinOp != Builtin::BI__lzcnt16 &&
+                             BuiltinOp != Builtin::BI__lzcnt &&
+                             BuiltinOp != Builtin::BI__lzcnt64;
+
+      if (ZeroIsUndefined)
+        return Error(E);
+    }
 
     return Success(Val.countl_zero(), E);
   }
@@ -12409,12 +12419,21 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
   case Builtin::BI__builtin_ctz:
   case Builtin::BI__builtin_ctzl:
   case Builtin::BI__builtin_ctzll:
-  case Builtin::BI__builtin_ctzs: {
+  case Builtin::BI__builtin_ctzs:
+  case Builtin::BI__builtin_ctzg: {
     APSInt Val;
     if (!EvaluateInteger(E->getArg(0), Val, Info))
       return false;
-    if (!Val)
+
+    if (!Val) {
+      if (BuiltinOp == Builtin::BI__builtin_ctzg && E->getNumArgs() > 1) {
+        if (!EvaluateInteger(E->getArg(1), Val, Info))
+          return false;
+        return Success(Val, E);
+      }
+
       return Error(E);
+    }
 
     return Success(Val.countr_zero(), E);
   }

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

@@ -218,6 +218,64 @@ char clz6[__builtin_clzll(0xFFLL) == BITSIZE(long long) - 8 ? 1 : -1];
 char clz7[__builtin_clzs(0x1) == BITSIZE(short) - 1 ? 1 : -1];
 char clz8[__builtin_clzs(0xf) == BITSIZE(short) - 4 ? 1 : -1];
 char clz9[__builtin_clzs(0xfff) == BITSIZE(short) - 12 ? 1 : -1];
+int clz10 = __builtin_clzg((unsigned char)0); // expected-error {{not a compile-time constant}}
+char clz11[__builtin_clzg((unsigned char)0, 42) == 42 ? 1 : -1];
+char clz12[__builtin_clzg((unsigned char)0x1) == BITSIZE(char) - 1 ? 1 : -1];
+char clz13[__builtin_clzg((unsigned char)0x1, 42) == BITSIZE(char) - 1 ? 1 : -1];
+char clz14[__builtin_clzg((unsigned char)0xf) == BITSIZE(char) - 4 ? 1 : -1];
+char clz15[__builtin_clzg((unsigned char)0xf, 42) == BITSIZE(char) - 4 ? 1 : -1];
+char clz16[__builtin_clzg((unsigned char)(1 << (BITSIZE(char) - 1))) == 0 ? 1 : -1];
+char clz17[__builtin_clzg((unsigned char)(1 << (BITSIZE(char) - 1)), 42) == 0 ? 1 : -1];
+int clz18 = __builtin_clzg((unsigned short)0); // expected-error {{not a compile-time constant}}
+char clz19[__builtin_clzg((unsigned short)0, 42) == 42 ? 1 : -1];
+char clz20[__builtin_clzg((unsigned short)0x1) == BITSIZE(short) - 1 ? 1 : -1];
+char clz21[__builtin_clzg((unsigned short)0x1, 42) == BITSIZE(short) - 1 ? 1 : -1];
+char clz22[__builtin_clzg((unsigned short)0xf) == BITSIZE(short) - 4 ? 1 : -1];
+char clz23[__builtin_clzg((unsigned short)0xf, 42) == BITSIZE(short) - 4 ? 1 : -1];
+char clz24[__builtin_clzg((unsigned short)(1 << (BITSIZE(short) - 1))) == 0 ? 1 : -1];
+char clz25[__builtin_clzg((unsigned short)(1 << (BITSIZE(short) - 1)), 42) == 0 ? 1 : -1];
+int clz26 = __builtin_clzg(0U); // expected-error {{not a compile-time constant}}
+char clz27[__builtin_clzg(0U, 42) == 42 ? 1 : -1];
+char clz28[__builtin_clzg(0x1U) == BITSIZE(int) - 1 ? 1 : -1];
+char clz29[__builtin_clzg(0x1U, 42) == BITSIZE(int) - 1 ? 1 : -1];
+char clz30[__builtin_clzg(0xfU) == BITSIZE(int) - 4 ? 1 : -1];
+char clz31[__builtin_clzg(0xfU, 42) == BITSIZE(int) - 4 ? 1 : -1];
+char clz32[__builtin_clzg(1U << (BITSIZE(int) - 1)) == 0 ? 1 : -1];
+char clz33[__builtin_clzg(1U << (BITSIZE(int) - 1), 42) == 0 ? 1 : -1];
+int clz34 = __builtin_clzg(0UL); // expected-error {{not a compile-time constant}}
+char clz35[__builtin_clzg(0UL, 42) == 42 ? 1 : -1];
+char clz36[__builtin_clzg(0x1UL) == BITSIZE(long) - 1 ? 1 : -1];
+char clz37[__builtin_clzg(0x1UL, 42) == BITSIZE(long) - 1 ? 1 : -1];
+char clz38[__builtin_clzg(0xfUL) == BITSIZE(long) - 4 ? 1 : -1];
+char clz39[__builtin_clzg(0xfUL, 42) == BITSIZE(long) - 4 ? 1 : -1];
+char clz40[__builtin_clzg(1UL << (BITSIZE(long) - 1)) == 0 ? 1 : -1];
+char clz41[__builtin_clzg(1UL << (BITSIZE(long) - 1), 42) == 0 ? 1 : -1];
+int clz42 = __builtin_clzg(0ULL); // expected-error {{not a compile-time constant}}
+char clz43[__builtin_clzg(0ULL, 42) == 42 ? 1 : -1];
+char clz44[__builtin_clzg(0x1ULL) == BITSIZE(long long) - 1 ? 1 : -1];
+char clz45[__builtin_clzg(0x1ULL, 42) == BITSIZE(long long) - 1 ? 1 : -1];
+char clz46[__builtin_clzg(0xfULL) == BITSIZE(long long) - 4 ? 1 : -1];
+char clz47[__builtin_clzg(0xfULL, 42) == BITSIZE(long long) - 4 ? 1 : -1];
+char clz48[__builtin_clzg(1ULL << (BITSIZE(long long) - 1)) == 0 ? 1 : -1];
+char clz49[__builtin_clzg(1ULL << (BITSIZE(long long) - 1), 42) == 0 ? 1 : -1];
+#ifdef __SIZEOF_INT128__
+int clz50 = __builtin_clzg((unsigned __int128)0); // expected-error {{not a compile-time constant}}
+char clz51[__builtin_clzg((unsigned __int128)0, 42) == 42 ? 1 : -1];
+char clz52[__builtin_clzg((unsigned __int128)0x1) == BITSIZE(__int128) - 1 ? 1 : -1];
+char clz53[__builtin_clzg((unsigned __int128)0x1, 42) == BITSIZE(__int128) - 1 ? 1 : -1];
+char clz54[__builtin_clzg((unsigned __int128)0xf) == BITSIZE(__int128) - 4 ? 1 : -1];
+char clz55[__builtin_clzg((unsigned __int128)0xf, 42) == BITSIZE(__int128) - 4 ? 1 : -1];
+char clz56[__builtin_clzg((unsigned __int128)(1 << (BITSIZE(__int128) - 1))) == 0 ? 1 : -1];
+char clz57[__builtin_clzg((unsigned __int128)(1 << (BITSIZE(__int128) - 1)), 42) == 0 ? 1 : -1];
+#endif
+int clz58 = __builtin_clzg((unsigned _BitInt(128))0); // expected-error {{not a compile-time constant}}
+char clz59[__builtin_clzg((unsigned _BitInt(128))0, 42) == 42 ? 1 : -1];
+char clz60[__builtin_clzg((unsigned _BitInt(128))0x1) == BITSIZE(_BitInt(128)) - 1 ? 1 : -1];
+char clz61[__builtin_clzg((unsigned _BitInt(128))0x1, 42) == BITSIZE(_BitInt(128)) - 1 ? 1 : -1];
+char clz62[__builtin_clzg((unsigned _BitInt(128))0xf) == BITSIZE(_BitInt(128)) - 4 ? 1 : -1];
+char clz63[__builtin_clzg((unsigned _BitInt(128))0xf, 42) == BITSIZE(_BitInt(128)) - 4 ? 1 : -1];
+char clz64[__builtin_clzg((unsigned _BitInt(128))(1 << (BITSIZE(_BitInt(128)) - 1))) == 0 ? 1 : -1];
+char clz65[__builtin_clzg((unsigned _BitInt(128))(1 << (BITSIZE(_BitInt(128)) - 1)), 42) == 0 ? 1 : -1];
 
 char ctz1[__builtin_ctz(1) == 0 ? 1 : -1];
 char ctz2[__builtin_ctz(8) == 3 ? 1 : -1];
@@ -226,6 +284,64 @@ int ctz4 = __builtin_ctz(0); // expected-error {{not a compile-time constant}}
 char ctz5[__builtin_ctzl(0x10L) == 4 ? 1 : -1];
 char ctz6[__builtin_ctzll(0x100LL) == 8 ? 1 : -1];
 char ctz7[__builtin_ctzs(1 << (BITSIZE(short) - 1)) == BITSIZE(short) - 1 ? 1 : -1];
+int ctz8 = __builtin_ctzg((unsigned char)0); // expected-error {{not a compile-time constant}}
+char ctz9[__builtin_ctzg((unsigned char)0, 42) == 42 ? 1 : -1];
+char ctz10[__builtin_ctzg((unsigned char)0x1) == 0 ? 1 : -1];
+char ctz11[__builtin_ctzg((unsigned char)0x1, 42) == 0 ? 1 : -1];
+char ctz12[__builtin_ctzg((unsigned char)0x10) == 4 ? 1 : -1];
+char ctz13[__builtin_ctzg((unsigned char)0x10, 42) == 4 ? 1 : -1];
+char ctz14[__builtin_ctzg((unsigned char)(1 << (BITSIZE(char) - 1))) == BITSIZE(char) - 1 ? 1 : -1];
+char ctz15[__builtin_ctzg((unsigned char)(1 << (BITSIZE(char) - 1)), 42) == BITSIZE(char) - 1 ? 1 : -1];
+int ctz16 = __builtin_ctzg((unsigned short)0); // expected-error {{not a compile-time constant}}
+char ctz17[__builtin_ctzg((unsigned short)0, 42) == 42 ? 1 : -1];
+char ctz18[__builtin_ctzg((unsigned short)0x1) == 0 ? 1 : -1];
+char ctz19[__builtin_ctzg((unsigned short)0x1, 42) == 0 ? 1 : -1];
+char ctz20[__builtin_ctzg((unsigned short)0x10) == 4 ? 1 : -1];
+char ctz21[__builtin_ctzg((unsigned short)0x10, 42) == 4 ? 1 : -1];
+char ctz22[__builtin_ctzg((unsigned short)(1 << (BITSIZE(short) - 1))) == BITSIZE(short) - 1 ? 1 : -1];
+char ctz23[__builtin_ctzg((unsigned short)(1 << (BITSIZE(short) - 1)), 42) == BITSIZE(short) - 1 ? 1 : -1];
+int ctz24 = __builtin_ctzg(0U); // expected-error {{not a compile-time constant}}
+char ctz25[__builtin_ctzg(0U, 42) == 42 ? 1 : -1];
+char ctz26[__builtin_ctzg(0x1U) == 0 ? 1 : -1];
+char ctz27[__builtin_ctzg(0x1U, 42) == 0 ? 1 : -1];
+char ctz28[__builtin_ctzg(0x10U) == 4 ? 1 : -1];
+char ctz29[__builtin_ctzg(0x10U, 42) == 4 ? 1 : -1];
+char ctz30[__builtin_ctzg(1U << (BITSIZE(int) - 1)) == BITSIZE(int) - 1 ? 1 : -1];
+char ctz31[__builtin_ctzg(1U << (BITSIZE(int) - 1), 42) == BITSIZE(int) - 1 ? 1 : -1];
+int ctz32 = __builtin_ctzg(0UL); // expected-error {{not a compile-time constant}}
+char ctz33[__builtin_ctzg(0UL, 42) == 42 ? 1 : -1];
+char ctz34[__builtin_ctzg(0x1UL) == 0 ? 1 : -1];
+char ctz35[__builtin_ctzg(0x1UL, 42) == 0 ? 1 : -1];
+char ctz36[__builtin_ctzg(0x10UL) == 4 ? 1 : -1];
+char ctz37[__builtin_ctzg(0x10UL, 42) == 4 ? 1 : -1];
+char ctz38[__builtin_ctzg(1UL << (BITSIZE(long) - 1)) == BITSIZE(long) - 1 ? 1 : -1];
+char ctz39[__builtin_ctzg(1UL << (BITSIZE(long) - 1), 42) == BITSIZE(long) - 1 ? 1 : -1];
+int ctz40 = __builtin_ctzg(0ULL); // expected-error {{not a compile-time constant}}
+char ctz41[__builtin_ctzg(0ULL, 42) == 42 ? 1 : -1];
+char ctz42[__builtin_ctzg(0x1ULL) == 0 ? 1 : -1];
+char ctz43[__builtin_ctzg(0x1ULL, 42) == 0 ? 1 : -1];
+char ctz44[__builtin_ctzg(0x10ULL) == 4 ? 1 : -1];
+char ctz45[__builtin_ctzg(0x10ULL, 42) == 4 ? 1 : -1];
+char ctz46[__builtin_ctzg(1ULL << (BITSIZE(long long) - 1)) == BITSIZE(long long) - 1 ? 1 : -1];
+char ctz47[__builtin_ctzg(1ULL << (BITSIZE(long long) - 1), 42) == BITSIZE(long long) - 1 ? 1 : -1];
+#ifdef __SIZEOF_INT128__
+int ctz48 = __builtin_ctzg((unsigned __int128)0); // expected-error {{not a compile-time constant}}
+char ctz49[__builtin_ctzg((unsigned __int128)0, 42) == 42 ? 1 : -1];
+char ctz50[__builtin_ctzg((unsigned __int128)0x1) == 0 ? 1 : -1];
+char ctz51[__builtin_ctzg((unsigned __int128)0x1, 42) == 0 ? 1 : -1];
+char ctz52[__builtin_ctzg((unsigned __int128)0x10) == 4 ? 1 : -1];
+char ctz53[__builtin_ctzg((unsigned __int128)0x10, 42) == 4 ? 1 : -1];
+char ctz54[__builtin_ctzg((unsigned __int128)1 << (BITSIZE(__int128) - 1)) == BITSIZE(__int128) - 1 ? 1 : -1];
+char ctz55[__builtin_ctzg((unsigned __int128)1 << (BITSIZE(__int128) - 1), 42) == BITSIZE(__int128) - 1 ? 1 : -1];
+#endif
+int ctz56 = __builtin_ctzg((unsigned _BitInt(128))0); // expected-error {{not a compile-time constant}}
+char ctz57[__builtin_ctzg((unsigned _BitInt(128))0, 42) == 42 ? 1 : -1];
+char ctz58[__builtin_ctzg((unsigned _BitInt(128))0x1) == 0 ? 1 : -1];
+char ctz59[__builtin_ctzg((unsigned _BitInt(128))0x1, 42) == 0 ? 1 : -1];
+char ctz60[__builtin_ctzg((unsigned _BitInt(128))0x10) == 4 ? 1 : -1];
+char ctz61[__builtin_ctzg((unsigned _BitInt(128))0x10, 42) == 4 ? 1 : -1];
+char ctz62[__builtin_ctzg((unsigned _BitInt(128))1 << (BITSIZE(_BitInt(128)) - 1)) == BITSIZE(_BitInt(128)) - 1 ? 1 : -1];
+char ctz63[__builtin_ctzg((unsigned _BitInt(128))1 << (BITSIZE(_BitInt(128)) - 1), 42) == BITSIZE(_BitInt(128)) - 1 ? 1 : -1];
 
 char popcount1[__builtin_popcount(0) == 0 ? 1 : -1];
 char popcount2[__builtin_popcount(0xF0F0) == 8 ? 1 : -1];