[clang][hlsl] Add atan2 intrinsic part 2

Issue: llvm#70096

Changes:
- `llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp` - Expand atan2 intrinsic using atan for DXIL.

llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp

@@ -35,6 +35,7 @@ using namespace llvm;
 static bool isIntrinsicExpansion(Function &F) {
   switch (F.getIntrinsicID()) {
   case Intrinsic::abs:
+  case Intrinsic::atan2:
   case Intrinsic::exp:
   case Intrinsic::log:
   case Intrinsic::log10:
@@ -305,6 +306,48 @@ static Value *expandNormalizeIntrinsic(CallInst *Orig) {
   return Builder.CreateFMul(X, MultiplicandVec);
 }
 
+static Value *expandAtan2Intrinsic(CallInst *Orig) {
+  Value *Y = Orig->getOperand(0);
+  Value *X = Orig->getOperand(1);
+  Type *Ty = X->getType();
+  IRBuilder<> Builder(Orig);
+
+  Value *Tan = Builder.CreateFDiv(Y, X);
+
+  Value *Atan =
+      Builder.CreateIntrinsic(Ty, Intrinsic::atan, {Tan}, nullptr, "Elt.Atan");
+
+  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);
+
+  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);
+
+  Value *XLt0AndYGe0 = Builder.CreateAnd(XLt0, YGe0);
+  Result = Builder.CreateSelect(XLt0AndYGe0, AtanAddPi, Result);
+
+  Value *XLt0AndYLt0 = Builder.CreateAnd(XLt0, YLt0);
+  Result = Builder.CreateSelect(XLt0AndYLt0, AtanSubPi, Result);
+
+  Value *XEq0AndYLt0 = Builder.CreateAnd(XEq0, YLt0);
+  Result = Builder.CreateSelect(XEq0AndYLt0, NegHalfPi, Result);
+
+  Value *XEq0AndYGe0 = Builder.CreateAnd(XEq0, YGe0);
+  Result = Builder.CreateSelect(XEq0AndYGe0, HalfPi, Result);
+
+  return Result;
+}
+
 static Value *expandPowIntrinsic(CallInst *Orig) {
 
   Value *X = Orig->getOperand(0);
@@ -394,6 +437,9 @@ static bool expandIntrinsic(Function &F, CallInst *Orig) {
   case Intrinsic::abs:
     Result = expandAbs(Orig);
     break;
+  case Intrinsic::atan2:
+    Result = expandAtan2Intrinsic(Orig);
+    break;
   case Intrinsic::exp:
     Result = expandExpIntrinsic(Orig);
     break;

llvm/test/CodeGen/DirectX/atan2.ll

@@ -0,0 +1,52 @@
+; RUN: opt -S -dxil-op-lower -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s
+
+; Make sure correct dxil expansions for atan2 are generated for float and half.
+
+define noundef float @atan2_float(float noundef %y, float noundef %x) {
+entry:
+; CHECK: [[DIV:%.+]] = fdiv float %y, %x
+; CHECK: [[TAN:%.+]] = call float @dx.op.unary.f32(i32 17, float [[DIV]])
+; CHECK-DAG: [[ADD_PI:%.+]] = fadd float [[TAN]], 0x400921FB60000000
+; CHECK-DAG: [[SUB_PI:%.+]] = fsub float [[TAN]], 0x400921FB60000000
+; CHECK-DAG: [[X_LT_0:%.+]] = fcmp olt float %x, 0.000000e+00
+; CHECK-DAG: [[X_EQ_0:%.+]] = fcmp oeq float %x, 0.000000e+00 
+; CHECK-DAG: [[Y_GE_0:%.+]] = fcmp oge float %y, 0.000000e+00 
+; CHECK-DAG: [[Y_LT_0:%.+]] = fcmp olt float %y, 0.000000e+00
+; CHECK: [[XLT0_AND_YGE0:%.+]] = and i1 [[X_LT_0]], [[Y_GE_0]]
+; CHECK: [[SELECT_ADD_PI:%.+]] = select i1 [[XLT0_AND_YGE0]], float [[ADD_PI]], float [[TAN]]
+; CHECK: [[XLT0_AND_YLT0:%.+]] = and i1 [[X_LT_0]], [[Y_LT_0]]
+; CHECK: [[SELECT_SUB_PI:%.+]] = select i1 [[XLT0_AND_YLT0]], float [[SUB_PI]], float [[SELECT_ADD_PI]]
+; CHECK: [[XEQ0_AND_YLT0:%.+]] = and i1 [[X_EQ_0]], [[Y_LT_0]]
+; CHECK: [[SELECT_NEGHPI:%.+]] = select i1 [[XEQ0_AND_YLT0]], float 0xBFF921FB60000000, float [[SELECT_SUB_PI]]
+; CHECK: [[XEQ0_AND_YGE0:%.+]] = and i1 [[X_EQ_0]], [[Y_GE_0]]
+; CHECK: [[SELECT_HPI:%.+]] = select i1 [[XEQ0_AND_YGE0]], float 0x3FF921FB60000000, float [[SELECT_NEGHPI]]
+; CHECK: ret float [[SELECT_HPI]]
+  %elt.atan2 = call float @llvm.atan2.f32(float %y, float %x)
+  ret float %elt.atan2
+}
+
+define noundef half @atan2_half(half noundef %y, half noundef %x) {
+entry:
+; CHECK: [[DIV:%.+]] = fdiv half %y, %x
+; CHECK: [[TAN:%.+]] = call half @dx.op.unary.f16(i32 17, half [[DIV]])
+; CHECK-DAG: [[ADD_PI:%.+]] = fadd half [[TAN]], 0xH4248
+; CHECK-DAG: [[SUB_PI:%.+]] = fsub half [[TAN]], 0xH4248
+; CHECK-DAG: [[X_LT_0:%.+]] = fcmp olt half %x, 0xH0000
+; CHECK-DAG: [[X_EQ_0:%.+]] = fcmp oeq half %x, 0xH0000 
+; CHECK-DAG: [[Y_GE_0:%.+]] = fcmp oge half %y, 0xH0000 
+; CHECK-DAG: [[Y_LT_0:%.+]] = fcmp olt half %y, 0xH0000
+; CHECK: [[XLT0_AND_YGE0:%.+]] = and i1 [[X_LT_0]], [[Y_GE_0]]
+; CHECK: [[SELECT_ADD_PI:%.+]] = select i1 [[XLT0_AND_YGE0]], half [[ADD_PI]], half [[TAN]]
+; CHECK: [[XLT0_AND_YLT0:%.+]] = and i1 [[X_LT_0]], [[Y_LT_0]]
+; CHECK: [[SELECT_SUB_PI:%.+]] = select i1 [[XLT0_AND_YLT0]], half [[SUB_PI]], half [[SELECT_ADD_PI]]
+; CHECK: [[XEQ0_AND_YLT0:%.+]] = and i1 [[X_EQ_0]], [[Y_LT_0]]
+; CHECK: [[SELECT_NEGHPI:%.+]] = select i1 [[XEQ0_AND_YLT0]], half 0xHBE48, half [[SELECT_SUB_PI]]
+; CHECK: [[XEQ0_AND_YGE0:%.+]] = and i1 [[X_EQ_0]], [[Y_GE_0]]
+; CHECK: [[SELECT_HPI:%.+]] = select i1 [[XEQ0_AND_YGE0]], half 0xH3E48, half [[SELECT_NEGHPI]]
+; CHECK: ret half [[SELECT_HPI]]
+  %elt.atan2 = call half @llvm.atan2.f16(half %y, half %x)
+  ret half %elt.atan2
+}
+
+declare half @llvm.atan2.f16(half, half)
+declare float @llvm.atan2.f32(float, float)

llvm/test/CodeGen/DirectX/atan2_error.ll

@@ -0,0 +1,11 @@
+; RUN: not opt -S -dxil-op-lower -mtriple=dxil-pc-shadermodel6.3-library %s 2>&1 | FileCheck %s
+
+; DXIL operation atan does not support double overload type
+; CHECK: in function atan2_double
+; CHECK-SAME: Cannot create ATan operation: Invalid overload type
+
+define noundef double @atan2_double(double noundef %a, double noundef %b) #0 {
+entry:
+  %1 = call double @llvm.atan2.f64(double %a, double %b)
+  ret double %1
+}