[clang] constexpr built-in reduce min/max function. (llvm#120866)

Part of llvm#51787.

This patch adds constexpr support for the built-in reduce min/max
function.

clang/docs/LanguageExtensions.rst

@@ -736,9 +736,10 @@ at the end to the next power of 2.
 
 These reductions support both fixed-sized and scalable vector types.
 
-The integer reduction intrinsics, including ``__builtin_reduce_add``,
-``__builtin_reduce_mul``, ``__builtin_reduce_and``, ``__builtin_reduce_or``,
-and ``__builtin_reduce_xor``, can be called in a ``constexpr`` context.
+The integer reduction intrinsics, including ``__builtin_reduce_max``,
+``__builtin_reduce_min``, ``__builtin_reduce_add``, ``__builtin_reduce_mul``,
+``__builtin_reduce_and``, ``__builtin_reduce_or``, and ``__builtin_reduce_xor``,
+can be called in a ``constexpr`` context.
 
 Example:
 

clang/docs/ReleaseNotes.rst

@@ -421,7 +421,8 @@ Non-comprehensive list of changes in this release
   ``__builtin_reduce_mul``, ``__builtin_reduce_and``, ``__builtin_reduce_or``,
   ``__builtin_reduce_xor``, ``__builtin_elementwise_popcount``,
   ``__builtin_elementwise_bitreverse``, ``__builtin_elementwise_add_sat``,
-  ``__builtin_elementwise_sub_sat``.
+  ``__builtin_elementwise_sub_sat``, ``__builtin_reduce_min`` (For integral element type),
+  ``__builtin_reduce_max`` (For integral element type).
 
 - Clang now rejects ``_BitInt`` matrix element types if the bit width is less than ``CHAR_WIDTH`` or
   not a power of two, matching preexisting behaviour for vector types.

clang/include/clang/Basic/Builtins.td

@@ -1462,13 +1462,13 @@ def ElementwiseSubSat : Builtin {
 
 def ReduceMax : Builtin {
   let Spellings = ["__builtin_reduce_max"];
-  let Attributes = [NoThrow, Const, CustomTypeChecking];
+  let Attributes = [NoThrow, Const, CustomTypeChecking, Constexpr];
   let Prototype = "void(...)";
 }
 
 def ReduceMin : Builtin {
   let Spellings = ["__builtin_reduce_min"];
-  let Attributes = [NoThrow, Const, CustomTypeChecking];
+  let Attributes = [NoThrow, Const, CustomTypeChecking, Constexpr];
   let Prototype = "void(...)";
 }
 

clang/lib/AST/ExprConstant.cpp

@@ -13604,7 +13604,9 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
   case Builtin::BI__builtin_reduce_mul:
   case Builtin::BI__builtin_reduce_and:
   case Builtin::BI__builtin_reduce_or:
-  case Builtin::BI__builtin_reduce_xor: {
+  case Builtin::BI__builtin_reduce_xor:
+  case Builtin::BI__builtin_reduce_min:
+  case Builtin::BI__builtin_reduce_max: {
     APValue Source;
     if (!EvaluateAsRValue(Info, E->getArg(0), Source))
       return false;
@@ -13641,6 +13643,14 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
         Reduced ^= Source.getVectorElt(EltNum).getInt();
         break;
       }
+      case Builtin::BI__builtin_reduce_min: {
+        Reduced = std::min(Reduced, Source.getVectorElt(EltNum).getInt());
+        break;
+      }
+      case Builtin::BI__builtin_reduce_max: {
+        Reduced = std::max(Reduced, Source.getVectorElt(EltNum).getInt());
+        break;
+      }
       }
     }
 

clang/test/Sema/constant_builtins_vector.cpp

@@ -798,6 +798,21 @@ static_assert(__builtin_reduce_xor((vector4long){(long long)0x1111111111111111L,
 static_assert(__builtin_reduce_xor((vector4uint){0x11111111U, 0x22222222U, 0x44444444U, 0x88888888U}) == 0xFFFFFFFFU);
 static_assert(__builtin_reduce_xor((vector4ulong){0x1111111111111111UL, 0x2222222222222222UL, 0x4444444444444444UL, 0x8888888888888888UL}) == 0xFFFFFFFFFFFFFFFFUL);
 
+static_assert(__builtin_reduce_min((vector4char){}) == 0);
+static_assert(__builtin_reduce_min((vector4char){(char)0x11, (char)0x22, (char)0x44, (char)0x88}) == (char)0x88);
+static_assert(__builtin_reduce_min((vector4short){(short)0x1111, (short)0x2222, (short)0x4444, (short)0x8888}) == (short)0x8888);
+static_assert(__builtin_reduce_min((vector4int){(int)0x11111111, (int)0x22222222, (int)0x44444444, (int)0x88888888}) == (int)0x88888888);
+static_assert(__builtin_reduce_min((vector4long){(long long)0x1111111111111111L, (long long)0x2222222222222222L, (long long)0x4444444444444444L, (long long)0x8888888888888888L}) == (long long)0x8888888888888888L);
+static_assert(__builtin_reduce_min((vector4uint){0x11111111U, 0x22222222U, 0x44444444U, 0x88888888U}) == 0x11111111U);
+static_assert(__builtin_reduce_min((vector4ulong){0x1111111111111111UL, 0x2222222222222222UL, 0x4444444444444444UL, 0x8888888888888888UL}) == 0x1111111111111111UL);
+static_assert(__builtin_reduce_max((vector4char){}) == 0);
+static_assert(__builtin_reduce_max((vector4char){(char)0x11, (char)0x22, (char)0x44, (char)0x88}) == (char)0x44);
+static_assert(__builtin_reduce_max((vector4short){(short)0x1111, (short)0x2222, (short)0x4444, (short)0x8888}) == (short)0x4444);
+static_assert(__builtin_reduce_max((vector4int){(int)0x11111111, (int)0x22222222, (int)0x44444444, (int)0x88888888}) == (int)0x44444444);
+static_assert(__builtin_reduce_max((vector4long){(long long)0x1111111111111111L, (long long)0x2222222222222222L, (long long)0x4444444444444444L, (long long)0x8888888888888888L}) == (long long)0x4444444444444444L);
+static_assert(__builtin_reduce_max((vector4uint){0x11111111U, 0x22222222U, 0x44444444U, 0x88888888U}) == 0x88888888U);
+static_assert(__builtin_reduce_max((vector4ulong){0x1111111111111111UL, 0x2222222222222222UL, 0x4444444444444444UL, 0x8888888888888888UL}) == 0x8888888888888888UL);
+
 static_assert(__builtin_bit_cast(unsigned, __builtin_elementwise_popcount((vector4char){1, 2, 3, 4})) == (LITTLE_END ? 0x01020101 : 0x01010201));
 static_assert(__builtin_bit_cast(unsigned long long, __builtin_elementwise_popcount((vector4short){0, 0x0F0F, ~0, ~0x0F0F})) == (LITTLE_END ? 0x0008001000080000 : 0x0000000800100008));
 static_assert(__builtin_reduce_add(__builtin_elementwise_popcount((vector4int){1, 2, 3, 4})) == 5);