[clang] [llvm] [HLSL] Add wave prefix count bits function (PR #178059)

[Tex Riddell via cfe-commits]

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@@ -864,6 +898,19 @@ Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID,
         CGM.getHLSLRuntime().getSaturateIntrinsic(), ArrayRef<Value *>{Op0},
         nullptr, "hlsl.saturate");
   }
+  case Builtin::BI__builtin_hlsl_wave_prefix_count_bits: {
+    Value *Op = EmitScalarExpr(E->getArg(0));
+    assert(Op->getType()->isIntegerTy(1) &&
+           "WavePrefixBitCount operand must be a boolean type");
+
+    Intrinsic::ID IID = getPrefixOpIntrinsic(
+        /* OpKind */ 136, getTarget().getTriple().getArch(),
+        CGM.getHLSLRuntime(), E->getArg(0)->getType());
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tex3d wrote:

I think we should have an independent code path for the bit count operation instead of passing a hard-coded DXIL OpCode as if it's an `OpKind` enumeration for the `WavePrefixOp`.

https://github.com/llvm/llvm-project/pull/178059