[llvm] Reenable sched mfma rewrite (PR #180751)

[Matt Arsenault via llvm-commits]

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@@ -1330,11 +1330,11 @@ bool RewriteMFMAFormStage::initGCNSchedStage() {
   if (!initHeuristics(RewriteCands, CopyForUse, CopyForDef))
     return false;
 
-  int64_t Cost = getRewriteCost(RewriteCands, CopyForUse, CopyForDef);
+  double Cost = getRewriteCost(RewriteCands, CopyForUse, CopyForDef);
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arsenm wrote:

Is there a concrete benefit or logic change? In general you're supposed to avoid FP in the compiler 

https://github.com/llvm/llvm-project/pull/180751