[clang] [HLSL] Implement the dst HLSL Function (PR #133828)

[Farzon Lotfi via cfe-commits]

================
@@ -0,0 +1,57 @@
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple dxil-pc-shadermodel6.2-library %s -fnative-half-type -emit-llvm -disable-llvm-passes -o - | FileCheck %s
+
+
+// CHECK-LABEL: linkonce_odr noundef nofpclass(nan inf) <4 x float> @_ZN4hlsl8__detail8dst_implIfEEDv4_T_S3_S3_(
+// CHECK-SAME: <4 x float> noundef nofpclass(nan inf) [[P:%.*]], <4 x float> noundef nofpclass(nan inf) [[Q:%.*]]) #[[ATTR0:[0-9]+]] { 
+// CHECK: [[VECEXT:%.*]] = extractelement <4 x float> [[PADDR:%.*]], i32 1
+// CHECK: [[VECEXT1:%.*]] = extractelement <4 x float> [[QADDR:%.*]], i32 1
+// CHECK: [[MULRES:%.*]] = fmul reassoc nnan ninf nsz arcp afn float [[VECEXT]], [[VECEXT1]]
----------------
farzonl wrote:

we have been very inconsistent here. I'm fine if this stays but have seen others wild card it out.

https://github.com/llvm/llvm-project/pull/133828