[llvm] [LV] Add initial legality checks for ee loops with stores (PR #145663)

[David Sherwood via llvm-commits]

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@@ -1793,6 +1814,110 @@ bool LoopVectorizationLegality::isVectorizableEarlyExitLoop() {
   return true;
 }
 
+bool LoopVectorizationLegality::canUncountedExitConditionLoadBeMoved(
+    BasicBlock *ExitingBlock) {
+  SmallVector<const SCEVPredicate *, 4> Predicates;
+  LoadInst *CriticalUncountedExitConditionLoad = nullptr;
+
+  // Try to find a load in the critical path for the uncounted exit condition.
+  // This is currently matching about the simplest form we can, expecting
+  // only one in-loop load, the result of which is directly compared against
+  // a loop-invariant value.
+  // FIXME: We're insisting on a single use for now, because otherwise we will
+  // need to make PHI nodes for other users. That can be done once the initial
+  // transform code lands.
+  if (BranchInst *Br = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) {
----------------
david-arm wrote:

nit: How about bailing out early if it's not a branch to remove some indentation? For example,

```
  auto *Br = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
  if (!Br) {
    reportVectorizationFailure(
        "Unsupported control flow in early exit loop with side effects",
        "Cannot find branch instruction for uncounted exit in early exit loop "
        "with side effects",
        "UnsupportedUncountedExitTerminator", ORE, TheLoop);
    return false;
  }

  // FIXME: Don't rely ...
```

https://github.com/llvm/llvm-project/pull/145663