[llvm] [AMDGPU] SIPeepholeSDWA: Disable on existing SDWA instructions (PR #123942)

[Frederik Harwath via llvm-commits]

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@@ -0,0 +1,85 @@
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx1030 -o - < %s | FileCheck -check-prefix=CHECK %s
+
+; CHECK-NOT: v_lshlrev_b32_sdwa v{{[0-9]}}, v{{[0-9]}}, v{{[0-9]}} dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:DWORD src1_sel:WORD_1
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frederik-h wrote:

I thought it is useful because it documents the reason of the test and if you run it on the baseline (as I did) it does match, but I can use update_llc_test_checks (which I did but I stripped the output a bit and added the `CHECK-NOT` line).
 The test has been reduced using llvm-reduce, using this as the check in the test script to ensure that the problematic sdwa instruction remains in the output:
```bash
llc  -mtriple=amdgcn-amd-amdhsa -mcpu=gfx1030  --stop-after=si-peephole-sdwa $1 -o - |& grep -E 'nsw V_LSHLREV_B32_sdwa 0, %[0-9]+, 0, %3, 0, 6, 0, 6, 5, implicit \$exec'
```

I could try to see what happens if I replace `%3` by `%[0-9]+`, too. I have not yet tried to simplify it further manually. 

https://github.com/llvm/llvm-project/pull/123942