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

[Jeffrey Byrnes via llvm-commits]

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@@ -435,6 +735,28 @@ bool SIPreEmitPeephole::run(MachineFunction &MF) {
   MF.RenumberBlocks();
 
   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()) {
+      for (MachineInstr *MI : InstrsToUnpack) {
+        if (!SIInstrInfo::modifiesModeRegister(*MI) &&
+            !MI->modifiesRegister(AMDGPU::EXEC, TRI))
+          performF32Unpacking(*MI);
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jrbyrnes wrote:

Are there cases where this interacts with branch optimization logic below?



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