[llvm] [DirectX] Add atan2 intrinsic and expand for DXIL backend (p1) (PR #108865)

[Farzon Lotfi via llvm-commits]

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+; RUN: opt -S -dxil-intrinsic-expansion -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s --check-prefixes=CHECK,EXPCHECK
+; RUN: opt -S -dxil-intrinsic-expansion -scalarizer -dxil-op-lower -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s --check-prefixes=CHECK,DOPCHECK
+
+; 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
+; EXPCHECK: [[ATAN:%.+]] = call float @llvm.atan.f32(float [[DIV]])
+; DOPCHECK: [[ATAN:%.+]] = call float @dx.op.unary.f32(i32 17, float [[DIV]])
+; CHECK-DAG: [[ADD_PI:%.+]] = fadd float [[ATAN]], 0x400921FB60000000
+; CHECK-DAG: [[SUB_PI:%.+]] = fsub float [[ATAN]], 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 [[ATAN]]
+; 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
+; EXPCHECK: [[ATAN:%.+]] = call half @llvm.atan.f16(half [[DIV]])
+; DOPCHECK: [[ATAN:%.+]] = call half @dx.op.unary.f16(i32 17, half [[DIV]])
+; CHECK-DAG: [[ADD_PI:%.+]] = fadd half [[ATAN]], 0xH4248
+; CHECK-DAG: [[SUB_PI:%.+]] = fsub half [[ATAN]], 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 [[ATAN]]
+; 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
+}
+
+define noundef <4 x float> @atan2_float4(<4 x float> noundef %y, <4 x float> noundef %x) {
+entry:
+; Just Expansion, no scalarization or lowering:
+; EXPCHECK: [[DIV:%.+]] = fdiv <4 x float> %y, %x
----------------
farzonl wrote:

this test isn't very useful using the EXPCHECK because we don't get to see if fcmp/and/select get scalarized. If you are going to include a vector test case then we should be using `DOPCHECK`

https://github.com/llvm/llvm-project/pull/108865