[llvm] [AMDGPU] Fix RewriteMFMAFormSchedStage (PR #193429)

[Matt Arsenault via llvm-commits]

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@@ -2354,6 +2361,38 @@ int64_t RewriteMFMAFormStage::getRewriteCost(
   unsigned AGPRThreshold = MaxVectorRegs.second;
   unsigned CombinedThreshold = ST.getMaxNumVGPRs(MF);
 
+  // Reset the classes that were changed to AGPR for better RB analysis.
+  // We must do rewriting after copy-insertion, as some defs of the register
+  // may require VGPR.  Additionally, if we bail out and don't perform the
+  // rewrite then these need to be restored anyway.
+  auto ResetRewriteCandsToVGPR =
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arsenm wrote:

Can move this to a separate helper function 

https://github.com/llvm/llvm-project/pull/193429