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

[Farzon Lotfi via llvm-commits]

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+; RUN: llc -O0 -mtriple=spirv-unknown-unknown %s -o - | FileCheck %s
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farzonl wrote:

This won't be a problem for opencl because they don't have a reflect api to trigger this crash. This could be a problem if folks try to target spirv32/spirv64 via c because we just exposed a clang builtin. Since we just enabled this  and are so far the only users of the spirv target builtins i'm not to worried about this.

That said there are a few ways we could address this.
1. remove the reflect spirv target builtin and wait for this pr to merge: https://github.com/llvm/llvm-project/pull/122839/files then add an instcombine pattern for `I - 2 * N * dot(I, N);` to map to reflect.
2. ignore this case
3. lower the intrinsic back to `I - 2 * N * dot(I, N);` if its not targeting GLSL.  (This is my least favorite option).

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