[llvm] [Analysis] Teach isDereferenceableAndAlignedInLoop about SCEV predicates (PR #106562)

[Igor Kirillov via llvm-commits]

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@@ -1331,11 +1331,17 @@ bool LoopVectorizationLegality::canVectorizeWithIfConvert() {
     // we restrict this to loads; stores are more complicated due to
     // concurrency restrictions.
     ScalarEvolution &SE = *PSE.getSE();
+    SmallVector<const SCEVPredicate *, 4> Predicates;
     for (Instruction &I : *BB) {
       LoadInst *LI = dyn_cast<LoadInst>(&I);
+      // Pass the Predicates pointer to isDereferenceableAndAlignedInLoop so
+      // that it will consider loops that need guarding by SCEV checks. The
+      // vectoriser will generate these checks if we decide to vectorise.
       if (LI && !LI->getType()->isVectorTy() && !mustSuppressSpeculation(*LI) &&
-          isDereferenceableAndAlignedInLoop(LI, TheLoop, SE, *DT, AC))
+          isDereferenceableAndAlignedInLoop(LI, TheLoop, SE, *DT, AC,
+                                            &Predicates))
         SafePointers.insert(LI->getPointerOperand());
+      Predicates.clear();
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igogo-x86 wrote:

I might not understand the full underlying magic, but I need help seeing a generation of the required predicates. As far as I understand, it is legal to put a pointer into `SafePointer` if `Predicates` would be generated before the vectorised loop, but I don't see any other code that collects those predicates again or generates them.

https://github.com/llvm/llvm-project/pull/106562