[llvm] unpack packed instructions overlapped by MFMAs post-RA scheduling (PR #157968)

[Jeffrey Byrnes via llvm-commits]

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@@ -483,5 +799,29 @@ bool SIPreEmitPeephole::run(MachineFunction &MF) {
     }
   }
 
+  // TODO: Fold this into previous block, if possible. Evaluate and handle any
+  // side effects.
+  for (MachineBasicBlock &MBB : MF) {
+    // Unpack packed instructions overlapped by MFMAs. This allows the compiler
+    // to co-issue unpacked instructions with MFMA
+    uint16_t NumMFMACycles = 0;
+    auto SchedModel = TII->getSchedModel();
+    SetVector<MachineInstr *> InstrsToUnpack;
+    for (auto &MI : make_early_inc_range(MBB.instrs())) {
+      if (SIInstrInfo::isMFMA(MI)) {
+        const MCSchedClassDesc *SchedClassDesc =
+            SchedModel.resolveSchedClass(&MI);
+        NumMFMACycles =
+            SchedModel.getWriteProcResBegin(SchedClassDesc)->ReleaseAtCycle;
+        collectUnpackingCandidates(MI, InstrsToUnpack, NumMFMACycles);
+      }
+    }
+    if (!InstrsToUnpack.empty()) {
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jrbyrnes wrote:

Redundant check for empty

https://github.com/llvm/llvm-project/pull/157968