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

[David Sherwood via llvm-commits]

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@@ -369,6 +377,36 @@ bool MachineLICMBase::runOnMachineFunction(MachineFunction &MF) {
   AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
 
   SmallVector<MachineLoop *, 8> Worklist(MLI->begin(), MLI->end());
+
+  // Initialize `AllowedToHoistLoads' if needed.
+  if (HoistConstLoads) {
+    auto TmpWorklist = Worklist;
+    // Initialize all loops with true values
+    while (!TmpWorklist.empty()) {
+      auto *L = TmpWorklist.pop_back_val();
+      AllowedToHoistLoads[L] = true;
+      TmpWorklist.insert(TmpWorklist.end(), L->getSubLoops().begin(),
+                         L->getSubLoops().end());
+    }
+    // Go through all the instructions inside top-level loops and, after finding
+    // one that makes it potentially unsafe to move loads, update load hoisting
+    // information for each loop containing this instruction.
+    for (auto *TopLoop : Worklist) {
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david-arm wrote:

Is it worth moving this loop into a small member function, i.e. something like `determineHoistableLoadLoops`? Not sure that's the best name though!

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