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

[Farzon Lotfi via cfe-commits]

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@@ -157,6 +158,42 @@ static bool expandAnyIntrinsic(CallInst *Orig) {
   return true;
 }
 
+static bool expandLengthIntrinsic(CallInst *Orig) {
+  Value *X = Orig->getOperand(0);
+  IRBuilder<> Builder(Orig->getParent());
+  Builder.SetInsertPoint(Orig);
+  Type *Ty = X->getType();
+  Type *EltTy = Ty->getScalarType();
+
+  // Though dx.length does work on scalar type, we can optimize it to just emit
+  // fabs, in CGBuiltin.cpp. We shouldn't see a scalar type here because
+  // CGBuiltin.cpp should have emitted a fabs call.
+  assert(Ty->isVectorTy() && "dx.length only works on vector type");
+  Value *Elt = Builder.CreateExtractElement(X, (uint64_t)0);
+  auto *XVec = dyn_cast<FixedVectorType>(Ty);
+  unsigned size = XVec->getNumElements();
+  if (size > 1) {
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farzonl wrote:

I don't think we will evert get a vector of size 1, that should just be a scalar which you have an assert for so I would delete this if statement. If you are really concerned you can add the size check to your assert. But whatever you decide delete the if.

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