[llvm] [AMDGPU] Per-chain MFMA->AGPR conversion (PR #217328)

[Matt Arsenault via llvm-commits]

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@@ -1377,6 +1385,56 @@ void RewriteMFMAFormStage::findReachingUses(
   }
 }
 
+/// Identify accumulator chains: groups of MFMAs connected via dst->src2.
+static SmallVector<SmallVector<unsigned, 8>, 16>
+identifyAccChains(ArrayRef<MachineInstr *> Cands, const SIInstrInfo *TII) {
+  DenseMap<Register, unsigned> DstToCand;
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arsenm wrote:

Use Register type 

https://github.com/llvm/llvm-project/pull/217328