[llvm] [LV] Initial support for stores in early exit loops (PR #137774)

[Graham Hunter via llvm-commits]

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@@ -1656,6 +1688,21 @@ bool LoopVectorizationLegality::isVectorizableEarlyExitLoop() {
         return false;
       }
 
+      // For loops with stores.
+      // Record load for analysis by isDereferenceableAndAlignedInLoop
+      // and later by dependence analysis.
+      if (BranchInst *Br = dyn_cast<BranchInst>(BB->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->contains(Load))
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huntergr-arm wrote:

So there shouldn't be a problem with stores since dependencies for the EarlyExitLoad are checked later (in canVectorizeMemory()), but I didn't check for a uniform load. I've added the !loopInvariant check for now.

Technically it would have been rejected by the vplan transformation and the plan deleted (since that's looking for a load with an address based on the canonical IV), but it's nice if we can reject earlier instead.

https://github.com/llvm/llvm-project/pull/137774