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

[Joshua Batista via cfe-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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bob80905 wrote:

No, didn't notice any behavioral differences, length.ll seems to behave consistently with scalars, and vectors with size 2 through 4.

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