[clang] Add __builtin_bitreverseg (PR #179126)

[Simon Pilgrim via cfe-commits]

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@@ -3683,6 +3683,16 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
     return RValue::get(
         emitBuiltinWithOneOverloadedType<1>(*this, E, Intrinsic::bswap));
   }
+  case Builtin::BI__builtin_bitreverseg: {
+    Value *ArgValue = EmitScalarExpr(E->getArg(0));
+    llvm::IntegerType *IntTy = cast<llvm::IntegerType>(ArgValue->getType());
+    assert(IntTy &&
+           "LLVM's __builtin_bitreverseg only support integer variants");
+    if (IntTy->getBitWidth() == 1)
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RKSimon wrote:

do you have test coverage for this case?

https://github.com/llvm/llvm-project/pull/179126