[clang] [llvm] [HLSL] Implement the `reflect` HLSL function (PR #122992)

[Farzon Lotfi via llvm-commits]

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@@ -3030,6 +3031,15 @@ bool SPIRVInstructionSelector::selectIntrinsic(Register ResVReg,
     return selectExtInst(ResVReg, ResType, I, CL::fract, GL::Fract);
   case Intrinsic::spv_normalize:
     return selectExtInst(ResVReg, ResType, I, CL::normalize, GL::Normalize);
+  case Intrinsic::spv_reflect:
+    if (!STI.canUseExtInstSet(SPIRV::InstructionSet::InstructionSet::GLSL_std_450)) {
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farzonl wrote:

I was hoping to put this conditional in the GL overloaded version of selectExtInst so that other GL only extention instructions could benefit.

https://github.com/llvm/llvm-project/pull/122992