[llvm] [MachineSink] Add capability for aggressive loop sinking (PR #117247)

[Matt Arsenault via llvm-commits]

================
@@ -787,48 +785,63 @@ bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
     EverMadeChange = true;
   }
 
-  if (SinkInstsIntoCycle || AggressivelySinkInstsIntoCycle) {
+  if (SinkInstsIntoCycle) {
     SmallVector<MachineCycle *, 8> Cycles(CI->toplevel_cycles());
+    SchedModel.init(STI);
+    enum CycleSinkStage { COPY, LOW_LATENCY, AGGRESSIVE, END };
 
-    DenseMap<std::pair<MachineInstr *, MachineBasicBlock *>, MachineInstr *>
-        SunkInstrs;
-    for (auto *Cycle : Cycles) {
-      MachineBasicBlock *Preheader = Cycle->getCyclePreheader();
-      if (!Preheader) {
-        LLVM_DEBUG(dbgs() << "CycleSink: Can't find preheader\n");
-        continue;
-      }
-      SmallVector<MachineInstr *, 8> Candidates;
-      FindCycleSinkCandidates(Cycle, Preheader, Candidates);
-
-      // Walk the candidates in reverse order so that we start with the use
-      // of a def-use chain, if there is any.
-      // TODO: Sort the candidates using a cost-model.
-      unsigned i = 0;
-
-      for (MachineInstr *I : llvm::reverse(Candidates)) {
-        // AggressivelySinkInstsIntoCycle sinks a superset of instructions
-        // relative to regular cycle sinking. Thus, this option supercedes
-        // captures all sinking opportunites done
-        if (AggressivelySinkInstsIntoCycle) {
-          aggressivelySinkIntoCycle(Cycle, *I, SunkInstrs);
-          EverMadeChange = true;
-          ++NumCycleSunk;
+    CycleSinkStage Stage = CycleSinkStage::COPY;
+    bool HasHighPressure;
+    do {
+      HasHighPressure = false;
+      DenseMap<std::pair<MachineInstr *, MachineBasicBlock *>, MachineInstr *>
+          SunkInstrs;
+      for (auto *Cycle : Cycles) {
+        MachineBasicBlock *Preheader = Cycle->getCyclePreheader();
+        if (!Preheader) {
+          LLVM_DEBUG(dbgs() << "CycleSink: Can't find preheader\n");
           continue;
         }
+        SmallVector<MachineInstr *, 8> Candidates;
+        FindCycleSinkCandidates(Cycle, Preheader, Candidates);
+
+        unsigned i = 0;
+
+        // Walk the candidates in reverse order so that we start with the use
+        // of a def-use chain, if there is any.
+        // TODO: Sort the candidates using a cost-model.
+        for (MachineInstr *I : llvm::reverse(Candidates)) {
+          // CycleSinkStage::COPY: Sink a limited number of copies
+          if (Stage == CycleSinkStage::COPY) {
+            if (i++ == SinkIntoCycleLimit) {
+              LLVM_DEBUG(dbgs()
+                         << "CycleSink:   Limit reached of instructions to "
+                            "be analysed.");
----------------
arsenm wrote:

```suggestion
                            "be analyzed\n");
```

Missing newline

https://github.com/llvm/llvm-project/pull/117247