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

[Simon Pilgrim via cfe-commits]

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@@ -11322,9 +11323,19 @@ 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())
+                        .extOrTrunc(Info.Ctx.getIntWidth(DestEltTy))));
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RKSimon wrote:

why do you need the extOrTrunc? Shouldn't the src/dst types be equal?

https://github.com/llvm/llvm-project/pull/118177