[clang] constexpr built-in reduce mul function. (#116626)

Part of #51787.
Follow up of #116243.

This patch adds constexpr support for the built-in reduce mul function.

Author: c8ef

clang/docs/ReleaseNotes.rst

@@ -356,6 +356,7 @@ Non-comprehensive list of changes in this release
   issues with the sanitizer because the counter is automatically set.
 
 - ``__builtin_reduce_add`` function can now be used in constant expressions.
+- ``__builtin_reduce_mul`` function can now be used in constant expressions.
 
 New Compiler Flags
 ------------------

clang/include/clang/Basic/Builtins.td

@@ -1510,7 +1510,7 @@ def ReduceAdd : Builtin {
 
 def ReduceMul : Builtin {
   let Spellings = ["__builtin_reduce_mul"];
-  let Attributes = [NoThrow, Const, CustomTypeChecking];
+  let Attributes = [NoThrow, Const, CustomTypeChecking, Constexpr];
   let Prototype = "void(...)";
 }
 

clang/lib/AST/ExprConstant.cpp

@@ -13527,18 +13527,33 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
     return Success(DidOverflow, E);
   }
 
-  case Builtin::BI__builtin_reduce_add: {
+  case Builtin::BI__builtin_reduce_add:
+  case Builtin::BI__builtin_reduce_mul: {
     APValue Source;
     if (!EvaluateAsRValue(Info, E->getArg(0), Source))
       return false;
 
     unsigned SourceLen = Source.getVectorLength();
     APSInt Reduced = Source.getVectorElt(0).getInt();
     for (unsigned EltNum = 1; EltNum < SourceLen; ++EltNum) {
-      if (!CheckedIntArithmetic(
-              Info, E, Reduced, Source.getVectorElt(EltNum).getInt(),
-              Reduced.getBitWidth() + 1, std::plus<APSInt>(), Reduced))
+      switch (BuiltinOp) {
+      default:
         return false;
+      case Builtin::BI__builtin_reduce_add: {
+        if (!CheckedIntArithmetic(
+                Info, E, Reduced, Source.getVectorElt(EltNum).getInt(),
+                Reduced.getBitWidth() + 1, std::plus<APSInt>(), Reduced))
+          return false;
+        break;
+      }
+      case Builtin::BI__builtin_reduce_mul: {
+        if (!CheckedIntArithmetic(
+                Info, E, Reduced, Source.getVectorElt(EltNum).getInt(),
+                Reduced.getBitWidth() * 2, std::multiplies<APSInt>(), Reduced))
+          return false;
+        break;
+      }
+      }
     }
 
     return Success(Reduced, E);

clang/test/Sema/constant_builtins_vector.cpp

@@ -745,3 +745,23 @@ constexpr long long reduceAddLong2 = __builtin_reduce_add((vector4long){(1LL <<
 // expected-note@-1 {{outside the range of representable values of type 'long long'}}
 static_assert(__builtin_reduce_add((vector4uint){~0U, 0, 0, 1}) == 0);
 static_assert(__builtin_reduce_add((vector4ulong){~0ULL, 0, 0, 1}) == 0);
+
+static_assert(__builtin_reduce_mul((vector4char){}) == 0);
+static_assert(__builtin_reduce_mul((vector4char){1, 2, 3, 4}) == 24);
+static_assert(__builtin_reduce_mul((vector4short){1, 2, 30, 40}) == 2400);
+static_assert(__builtin_reduce_mul((vector4int){10, 20, 300, 400}) == 24000000);
+static_assert(__builtin_reduce_mul((vector4long){1000L, 2000L, 3000L, 4000L}) == 24000000000000L);
+constexpr int reduceMulInt1 = __builtin_reduce_mul((vector4int){~(1 << 31), 1, 1, 2});
+// expected-error@-1 {{must be initialized by a constant expression}} \
+// expected-note@-1 {{outside the range of representable values of type 'int'}}
+constexpr long long reduceMulLong1 = __builtin_reduce_mul((vector4long){~(1LL << 63), 1, 1, 2});
+// expected-error@-1 {{must be initialized by a constant expression}} \
+// expected-note@-1 {{outside the range of representable values of type 'long long'}}
+constexpr int reduceMulInt2 = __builtin_reduce_mul((vector4int){(1 << 31), 1, 1, 2});
+// expected-error@-1 {{must be initialized by a constant expression}} \
+// expected-note@-1 {{outside the range of representable values of type 'int'}}
+constexpr long long reduceMulLong2 = __builtin_reduce_mul((vector4long){(1LL << 63), 1, 1, 2});
+// expected-error@-1 {{must be initialized by a constant expression}} \
+// expected-note@-1 {{outside the range of representable values of type 'long long'}}
+static_assert(__builtin_reduce_mul((vector4uint){~0U, 1, 1, 2}) == ~0U - 1);
+static_assert(__builtin_reduce_mul((vector4ulong){~0ULL, 1, 1, 2}) == ~0ULL - 1);