[llvm] [AMDGPU][NFC]:: Minor Unpacking Fixes. (PR #163992)

[Jeffrey Byrnes via llvm-commits]

================
@@ -787,22 +770,26 @@ 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
-    auto SchedModel = TII->getSchedModel();
-    SetVector<MachineInstr *> InstrsToUnpack;
-    for (auto &MI : make_early_inc_range(MBB.instrs())) {
-      if (!SIInstrInfo::isMFMA(MI))
-        continue;
-      const MCSchedClassDesc *SchedClassDesc =
-          SchedModel.resolveSchedClass(&MI);
-      uint16_t NumMFMACycles =
-          SchedModel.getWriteProcResBegin(SchedClassDesc)->ReleaseAtCycle;
-      collectUnpackingCandidates(MI, InstrsToUnpack, NumMFMACycles);
-    }
-    for (MachineInstr *MI : InstrsToUnpack) {
-      performF32Unpacking(*MI);
+
+  // Perform the extra MF scans only for supported archs
+  if (ST.hasGFX940Insts()) {
----------------
jrbyrnes wrote:

Use early exit to reduce nesting https://llvm.org/docs/CodingStandards.html#use-early-exits-and-continue-to-simplify-code
 
```
if (!ST.hasGFX9540Insts())
    return Changed;

for (MachineBasicBlock &MBB : MF) {
...
```

https://github.com/llvm/llvm-project/pull/163992