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

[Florian Hahn via llvm-commits]

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@@ -1781,6 +1803,109 @@ bool LoopVectorizationLegality::isVectorizableEarlyExitLoop() {
                        "backedge taken count: "
                     << *SymbolicMaxBTC << '\n');
   UncountableExitingBB = SingleUncountableExitingBlock;
+  UncountedExitWithSideEffects = HasSideEffects;
+  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.
+  auto *Br = cast<BranchInst>(ExitingBlock->getTerminator());
+
+  // FIXME: Don't rely on operand ordering for the comparison.
+  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()) {
+      // Make sure that the load address is not loop invariant; we want an
+      // address calculation that we can rotate to the next vector iteration.
+      const SCEV *PtrScev = PSE.getSE()->getSCEV(Load->getPointerOperand());
+      if (PSE.getSE()->isLoopInvariant(PtrScev, TheLoop)) {
+        reportVectorizationFailure(
+            "Uncounted exit condition depends on load from invariant address",
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fhahn wrote:

looks like there's no test coverage for that check.

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