[clang] [llvm] [HLSL] implement elementwise firstbithigh hlsl builtin (PR #111082)

[Farzon Lotfi via cfe-commits]

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@@ -37,13 +39,12 @@ define noundef i32 @firstbituhigh_i64(i64 noundef %a) {
 entry:
 ; CHECK: [[O:%.*]] = OpBitcast %[[#]] %[[#]]
 ; CHECK: [[N:%.*]] = OpExtInst %[[#]] %[[#]] FindUMsb [[O]]
-; CHECK: [[M:%.*]] = OpVectorShuffle %[[#]] [[N]] [[N]] 0
-; CHECK: [[L:%.*]] = OpVectorShuffle %[[#]] [[N]] [[N]] 1
+; CHECK: [[M:%.*]] = OpVectorExtractDynamic %[[#]] [[N]] [[Z]]
+; CHECK: [[L:%.*]] = OpVectorExtractDynamic %[[#]] [[N]] [[X]]
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farzonl wrote:

This looks right. Could you document the reason for the `OpVectorShuffle` ti `OpVectorExtractDynamic`. As a response to this comment.

https://github.com/llvm/llvm-project/pull/111082