[llvm] [x86] Add lowering for `@llvm.experimental.vector.compress` (PR #104904)

[Simon Pilgrim via llvm-commits]

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@@ -0,0 +1,689 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -O1 -mtriple=x86_64 -mattr=+avx2                             < %s | FileCheck %s --check-prefixes=CHECK,AVX2
+; RUN: llc -O1 -mtriple=x86_64 -mattr=+avx512f,+avx512vl,+avx512vbmi2 < %s | FileCheck %s --check-prefixes=CHECK,AVX512
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RKSimon wrote:

Drop -O1 and add a -mattr=+avx512f only RUN:
```
; RUN: llc -mtriple=x86_64-- -mattr=+avx2                           < %s | FileCheck %s --check-prefixes=CHECK,AVX2
; RUN: llc -mtriple=x86_64-- -mattr=+avx512f,                       < %s | FileCheck %s --check-prefixes=CHECK,AVX512,AVX512F
; RUN: llc -mtriple=x86_64-- -mattr=+avx512f,+avx512vl,+avx512vbmi2 < %s | FileCheck %s --check-prefixes=CHECK,AVX512,AVX512VL
```

https://github.com/llvm/llvm-project/pull/104904