[llvm] [AMDGPU][MC]FMA-mix instructions should not be supported in GFX908 etc. (PR #109873)

[Matt Arsenault via llvm-commits]

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@@ -1426,7 +1425,6 @@ def FeatureISAVersion9_4_Common : FeatureSet<
   [FeatureGFX9,
    FeatureGFX90AInsts,
    FeatureGFX940Insts,
-   FeatureFmaMixInsts,
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arsenm wrote:

That's what I thought, but looking at the manual there is no mention of FMA in any of the MI manuals. gfx906 did the ugly mad->fma encoding switch, but all of the 908/90a/940 manuals only talk about mad 

https://github.com/llvm/llvm-project/pull/109873