[llvm] [AMDGPU] Precommit test for issue in amdgpu-rewrite-agpr-copy-mfma, (PR #168609)

[Matt Arsenault via llvm-commits]

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+# RUN: not llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx950 -run-pass=greedy,amdgpu-rewrite-agpr-copy-mfma -verify-machineinstrs -o - %s 2>&1 | FileCheck %s
+# CHECK: Illegal virtual register for instruction
+# CHECK: Expected a VGPR_32 register, but got a AGPR_32 register
+
+# Test for issue in amdgpu-rewrite-agpr-copy-mfma, which reassigns scale operand
+# in vgpr_32 register to agpr_32, not permitted by instruction format.
+--- |
+  define amdgpu_kernel void @test() #0 {
+  entry:
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arsenm wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/168609