[llvm] [AMDGPU] Pre-commit fdot2 test. NFC. (PR #72622)

[Matt Arsenault via llvm-commits]

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@@ -72,4 +72,23 @@ entry:
   ret void
 }
 
+; FIXME: This test violates constant bus restriction.
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arsenm wrote:

So this test will fail the verifier? Does it need to start in a separate xfailed test?

https://github.com/llvm/llvm-project/pull/72622