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

[Stanislav Mekhanoshin 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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rampitec wrote:

I.e. this is a bug very hard to run into.

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