[llvm] [MachineLICM] Allow hoisting loads from invariant address (PR #70796)

[David Sherwood via llvm-commits]

================
@@ -772,6 +779,32 @@ void MachineLICMBase::HoistOutOfLoop(MachineDomTreeNode *HeaderN,
   BackTrace.clear();
   InitRegPressure(Preheader);
 
+  // Compute information about whether it is allowed to move load instruction
+  // out of the current loop or one of the inner loops
+  SmallDenseMap<MachineLoop *, bool> AllowedToHoistLoads;
+  if (HoistConstLoads) {
+    SmallVector<MachineLoop *, 4> Worklist{CurLoop};
+
+    while (!Worklist.empty()) {
----------------
david-arm wrote:

I think we already have this worklist in `runOnMachineFunction`:

  `SmallVector<MachineLoop *, 8> Worklist(MLI->begin(), MLI->end());`

If you set up the map there instead you can reduce the amount of extra work needed, for example in `runOnMachineFunction` you could do

```
for (auto *Loop : Worklist) {
  for (auto &MI : *MBB) {
    ...
  }
}
```


https://github.com/llvm/llvm-project/pull/70796