[DXIL] Add frac unary lowering (#83465)

This change adds lowering for HLSL's frac intrinsic to DXIL.

This change should complete #70099

Author: farzonl

llvm/lib/Target/DirectX/DXIL.td

@@ -218,6 +218,9 @@ class DXILOpMapping<int opCode, DXILOpClass opClass, Intrinsic intrinsic, string
 // Concrete definition of DXIL Operation mapping to corresponding LLVM intrinsic
 def Sin  : DXILOpMapping<13, unary, int_sin,
                          "Returns sine(theta) for theta in radians.">;
+def Frac : DXILOpMapping<22, unary, int_dx_frac,
+                         "Returns a fraction from 0 to 1 that represents the "
+                         "decimal part of the input.">;
 def Round : DXILOpMapping<26, unary, int_round,
                          "Returns the input rounded to the nearest integer"
                          "within a floating-point type.">;

llvm/test/CodeGen/DirectX/frac.ll

@@ -0,0 +1,34 @@
+; RUN: opt -S -dxil-op-lower < %s | FileCheck %s
+
+; Make sure dxil operation function calls for frac are generated for float and half.
+; CHECK:call float @dx.op.unary.f32(i32 22, float %{{.*}})
+; CHECK:call half @dx.op.unary.f16(i32 22, half %{{.*}})
+
+target datalayout = "e-m:e-p:32:32-i1:32-i8:8-i16:16-i32:32-i64:64-f16:16-f32:32-f64:64-n8:16:32:64"
+target triple = "dxil-pc-shadermodel6.7-library"
+
+; Function Attrs: noinline nounwind optnone
+define noundef float @frac_float(float noundef %a) #0 {
+entry:
+  %a.addr = alloca float, align 4
+  store float %a, ptr %a.addr, align 4
+  %0 = load float, ptr %a.addr, align 4
+  %dx.frac = call float @llvm.dx.frac.f32(float %0)
+  ret float %dx.frac
+}
+
+; Function Attrs: nocallback nofree nosync nounwind readnone speculatable willreturn
+declare float @llvm.dx.frac.f32(float) #1
+
+; Function Attrs: noinline nounwind optnone
+define noundef half @frac_half(half noundef %a) #0 {
+entry:
+  %a.addr = alloca half, align 2
+  store half %a, ptr %a.addr, align 2
+  %0 = load half, ptr %a.addr, align 2
+  %dx.frac = call half @llvm.dx.frac.f16(half %0)
+  ret half %dx.frac
+}
+
+; Function Attrs: nocallback nofree nosync nounwind readnone speculatable willreturn
+declare half @llvm.dx.frac.f16(half) #1