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

[Matt Arsenault 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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arsenm wrote:

A comment explaining what the test is doing would be more useful 

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