[clang] [llvm] Add length HLSL function to DirectX Backend (PR #101256)

[Farzon Lotfi via llvm-commits]

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@@ -18460,6 +18460,22 @@ Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID,
         /*ReturnType=*/X->getType(), CGM.getHLSLRuntime().getLerpIntrinsic(),
         ArrayRef<Value *>{X, Y, S}, nullptr, "hlsl.lerp");
   }
+  case Builtin::BI__builtin_hlsl_elementwise_length: {
+    Value *X = EmitScalarExpr(E->getArg(0));
+    
+    if (!E->getArg(0)->getType()->hasFloatingRepresentation())
+      llvm_unreachable("length operand must have a float representation");
+    // if the operand is a scalar, we can use the fabs llvm intrinsic directly
+    if (!E->getArg(0)->getType()->isVectorType()) {
+      llvm::Type *ResultType = ConvertType(E->getType());
+      Function *F = CGM.getIntrinsic(Intrinsic::fabs, ResultType);
+      return Builder.CreateCall(F, X);
+    }
+    return Builder.CreateIntrinsic(
+        /*ReturnType=*/X->getType()->getScalarType(),
+        CGM.getHLSLRuntime().getLengthIntrinsic(),
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farzonl wrote:

This looks right, but did you notice any behavioral differences because the intrinsics were not defined the same? Just curious? Maybe the issue i'm worried about would become more clear when you start the SPIRV backend changes.

https://github.com/llvm/llvm-project/pull/101256