[llvm] [AMDGPU] Fix illegal AGPR reclassification in RewriteMFMAFormStage (PR #200972)

[Petr Kurapov via llvm-commits]

================
@@ -2263,6 +2265,25 @@ static bool isReachingDefAGPRForm(MachineInstr *RD,
   return false;
 }
 
+bool RewriteMFMAFormStage::hasUseRequiringVGPR(
+    ArrayRef<SlotIndex> Src2ReachingDefs,
+    const SmallPtrSetImpl<MachineInstr *> &RewriteSet) {
+  for (SlotIndex RDIdx : Src2ReachingDefs) {
+    const MachineInstr *RD = DAG.LIS->getInstructionFromIndex(RDIdx);
+    SmallVector<MachineOperand *, 8> ReachingUses;
+    findReachingUses(RD, DAG.LIS, ReachingUses);
----------------
kurapov-peter wrote:

So this is gonna run per candidate and for each use look for reaching defs. Can the info be at least reused between heuristic init and the rewrite?

https://github.com/llvm/llvm-project/pull/200972