Address feedback for DXILIntrinsicExpansion.cpp

Author: tex3d

llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp

@@ -313,37 +313,43 @@ static Value *expandAtan2Intrinsic(CallInst *Orig) {
   Value *X = Orig->getOperand(1);
   Type *Ty = X->getType();
   IRBuilder<> Builder(Orig);
+  Builder.setFastMathFlags(Orig->getFastMathFlags());
 
   Value *Tan = Builder.CreateFDiv(Y, X);
 
-  Value *Atan =
+  CallInst *Atan =
       Builder.CreateIntrinsic(Ty, Intrinsic::atan, {Tan}, nullptr, "Elt.Atan");
+  Atan->setTailCall(Orig->isTailCall());
+  Atan->setAttributes(Orig->getAttributes());
 
+  // Modify atan result based on https://en.wikipedia.org/wiki/Atan2.
   Constant *Pi = ConstantFP::get(Ty, llvm::numbers::pi);
   Constant *HalfPi = ConstantFP::get(Ty, llvm::numbers::pi / 2);
   Constant *NegHalfPi = ConstantFP::get(Ty, -llvm::numbers::pi / 2);
   Constant *Zero = ConstantFP::get(Ty, 0);
-
   Value *AtanAddPi = Builder.CreateFAdd(Atan, Pi);
   Value *AtanSubPi = Builder.CreateFSub(Atan, Pi);
 
+  // x > 0 -> atan.
   Value *Result = Atan;
-
   Value *XLt0 = Builder.CreateFCmpOLT(X, Zero);
   Value *XEq0 = Builder.CreateFCmpOEQ(X, Zero);
-
   Value *YGe0 = Builder.CreateFCmpOGE(Y, Zero);
   Value *YLt0 = Builder.CreateFCmpOLT(Y, Zero);
 
+  // x < 0, y >= 0 -> atan + pi.
   Value *XLt0AndYGe0 = Builder.CreateAnd(XLt0, YGe0);
   Result = Builder.CreateSelect(XLt0AndYGe0, AtanAddPi, Result);
 
+  // x < 0, y < 0 -> atan - pi.
   Value *XLt0AndYLt0 = Builder.CreateAnd(XLt0, YLt0);
   Result = Builder.CreateSelect(XLt0AndYLt0, AtanSubPi, Result);
 
+  // x == 0, y < 0 -> -pi/2
   Value *XEq0AndYLt0 = Builder.CreateAnd(XEq0, YLt0);
   Result = Builder.CreateSelect(XEq0AndYLt0, NegHalfPi, Result);
 
+  // x == 0, y > 0 -> pi/2
   Value *XEq0AndYGe0 = Builder.CreateAnd(XEq0, YGe0);
   Result = Builder.CreateSelect(XEq0AndYGe0, HalfPi, Result);