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

[Graham Hunter via llvm-commits]

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@@ -1771,13 +1815,63 @@ bool LoopVectorizationLegality::isVectorizableEarlyExitLoop() {
 
   // TODO: Handle loops that may fault.
   Predicates.clear();
-  if (!isDereferenceableReadOnlyLoop(TheLoop, PSE.getSE(), DT, AC,
-                                     &Predicates)) {
-    reportVectorizationFailure(
-        "Loop may fault",
-        "Cannot vectorize potentially faulting early exit loop",
-        "PotentiallyFaultingEarlyExitLoop", ORE, TheLoop);
-    return false;
+  if (UncountedExitWithSideEffects) {
+    // Record load for analysis by isDereferenceableAndAlignedInLoop
+    // and later by dependence analysis.
+    if (BranchInst *Br = dyn_cast<BranchInst>(
+            SingleUncountableEdge->first->getTerminator())) {
+      // FIXME: Handle exit conditions with multiple users, more complex exit
+      //        conditions than br(icmp(load, loop_inv)).
+      ICmpInst *Cmp = dyn_cast<ICmpInst>(Br->getCondition());
+      if (Cmp && Cmp->hasOneUse() &&
+          TheLoop->isLoopInvariant(Cmp->getOperand(1))) {
+        LoadInst *Load = dyn_cast<LoadInst>(Cmp->getOperand(0));
+        if (Load && Load->hasOneUse() && !TheLoop->isLoopInvariant(Load)) {
+          if (isDereferenceableAndAlignedInLoop(Load, TheLoop, *PSE.getSE(),
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huntergr-arm wrote:

I'll write an in-code comment explaining the intended transformation to hopefully make it easier to gauge whether the checks are sufficient.

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