[clang] constexpr built-in elementwise bitreverse function. (#118177)

Part of #51787.

This patch adds constexpr support for the built-in elementwise
bitreverse function.

Author: c8ef

clang/docs/LanguageExtensions.rst

@@ -648,7 +648,7 @@ elementwise to the input.
 Unless specified otherwise operation(±0) = ±0 and operation(±infinity) = ±infinity
 
 The integer elementwise intrinsics, including ``__builtin_elementwise_popcount``,
-can be called in a ``constexpr`` context.
+``__builtin_elementwise_bitreverse``, can be called in a ``constexpr`` context.
 
 ============================================== ====================================================================== =========================================
          Name                                   Operation                                                             Supported element types

clang/docs/ReleaseNotes.rst

@@ -404,6 +404,7 @@ Non-comprehensive list of changes in this release
 - ``__builtin_reduce_and`` function can now be used in constant expressions.
 - ``__builtin_reduce_or`` and ``__builtin_reduce_xor`` functions can now be used in constant expressions.
 - ``__builtin_elementwise_popcount`` function can now be used in constant expressions.
+- ``__builtin_elementwise_bitreverse`` function can now be used in constant expressions.
 
 New Compiler Flags
 ------------------

clang/include/clang/Basic/Builtins.td

@@ -1270,7 +1270,7 @@ def ElementwiseATan2 : Builtin {
 
 def ElementwiseBitreverse : Builtin {
   let Spellings = ["__builtin_elementwise_bitreverse"];
-  let Attributes = [NoThrow, Const, CustomTypeChecking];
+  let Attributes = [NoThrow, Const, CustomTypeChecking, Constexpr];
   let Prototype = "void(...)";
 }
 

clang/lib/AST/ExprConstant.cpp

@@ -11310,7 +11310,8 @@ bool VectorExprEvaluator::VisitCallExpr(const CallExpr *E) {
   switch (E->getBuiltinCallee()) {
   default:
     return false;
-  case Builtin::BI__builtin_elementwise_popcount: {
+  case Builtin::BI__builtin_elementwise_popcount:
+  case Builtin::BI__builtin_elementwise_bitreverse: {
     APValue Source;
     if (!EvaluateAsRValue(Info, E->getArg(0), Source))
       return false;
@@ -11322,9 +11323,18 @@ bool VectorExprEvaluator::VisitCallExpr(const CallExpr *E) {
 
     for (unsigned EltNum = 0; EltNum < SourceLen; ++EltNum) {
       APSInt Elt = Source.getVectorElt(EltNum).getInt();
-      ResultElements.push_back(
-          APValue(APSInt(APInt(Info.Ctx.getIntWidth(DestEltTy), Elt.popcount()),
-                         DestEltTy->isUnsignedIntegerOrEnumerationType())));
+      switch (E->getBuiltinCallee()) {
+      case Builtin::BI__builtin_elementwise_popcount:
+        ResultElements.push_back(APValue(
+            APSInt(APInt(Info.Ctx.getIntWidth(DestEltTy), Elt.popcount()),
+                   DestEltTy->isUnsignedIntegerOrEnumerationType())));
+        break;
+      case Builtin::BI__builtin_elementwise_bitreverse:
+        ResultElements.push_back(
+            APValue(APSInt(Elt.reverseBits(),
+                           DestEltTy->isUnsignedIntegerOrEnumerationType())));
+        break;
+      }
     }
 
     return Success(APValue(ResultElements.data(), ResultElements.size()), E);
@@ -12833,7 +12843,8 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
   case Builtin::BI__builtin_bitreverse8:
   case Builtin::BI__builtin_bitreverse16:
   case Builtin::BI__builtin_bitreverse32:
-  case Builtin::BI__builtin_bitreverse64: {
+  case Builtin::BI__builtin_bitreverse64:
+  case Builtin::BI__builtin_elementwise_bitreverse: {
     APSInt Val;
     if (!EvaluateInteger(E->getArg(0), Val, Info))
       return false;

clang/test/CodeGen/builtins-elementwise-math.c

@@ -443,7 +443,7 @@ void test_builtin_elementwise_bitreverse(si8 vi1, si8 vi2,
   // CHECK-NEXT: call i32 @llvm.bitreverse.i32(i32 [[IA1]])
   b = __builtin_elementwise_bitreverse(int_as_one);
 
-  // CHECK:   call i32 @llvm.bitreverse.i32(i32 -10)
+  // CHECK:      store i32 1879048191, ptr @b, align 4
   b = __builtin_elementwise_bitreverse(-10);
 
   // CHECK:      [[SI:%.+]] = load i16, ptr %si.addr, align 2

clang/test/Sema/constant_builtins_vector.cpp

@@ -817,3 +817,8 @@ static_assert(__builtin_elementwise_popcount(~0U) == 8 * sizeof(int));
 static_assert(__builtin_elementwise_popcount(0L) == 0);
 static_assert(__builtin_elementwise_popcount(0xF0F0L) == 8);
 static_assert(__builtin_elementwise_popcount(~0LL) == 8 * sizeof(long long));
+
+static_assert(__builtin_elementwise_bitreverse(0x12345678) == 0x1E6A2C48);
+static_assert(__builtin_elementwise_bitreverse(0x0123456789ABCDEFULL) == 0xF7B3D591E6A2C480);
+static_assert(__builtin_bit_cast(unsigned, __builtin_elementwise_bitreverse((vector4char){1, 2, 4, 8})) == (LITTLE_END ? 0x10204080 : 0x80402010));
+static_assert(__builtin_bit_cast(unsigned long long, __builtin_elementwise_bitreverse((vector4short){1, 2, 4, 8})) == (LITTLE_END ? 0x1000200040008000 : 0x8000400020001000));