[llvm-branch-commits] [llvm] [LV] Mask off possibly aliasing vector lanes (PR #100579)

[Benjamin Maxwell via llvm-branch-commits]

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@@ -1300,14 +1301,38 @@ static VPActiveLaneMaskPHIRecipe *addVPLaneMaskPhiAndUpdateExitBranch(
       cast<VPInstruction>(CanonicalIVPHI->getBackedgeValue());
   // TODO: Check if dropping the flags is needed if
   // !DataAndControlFlowWithoutRuntimeCheck.
+  VPValue *IncVal = CanonicalIVIncrement->getOperand(1);
+  assert(IncVal != CanonicalIVPHI && "Unexpected operand order");
+
   CanonicalIVIncrement->dropPoisonGeneratingFlags();
   DebugLoc DL = CanonicalIVIncrement->getDebugLoc();
+
   // We can't use StartV directly in the ActiveLaneMask VPInstruction, since
   // we have to take unrolling into account. Each part needs to start at
   //   Part * VF
   auto *VecPreheader = Plan.getVectorPreheader();
   VPBuilder Builder(VecPreheader);
 
+  // Create an alias mask for each possibly-aliasing pointer pair. If there
+  // are multiple they are combined together with ANDs.
+  VPValue *AliasMask = nullptr;
+
+  for (auto C : RTChecks) {
+    // FIXME: How to pass this info back?
+    //    HasAliasMask = true;
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MacDue wrote:

This FIXME is a little unclear. Does it mean `HasAliasMask` should be set here but it's not?

https://github.com/llvm/llvm-project/pull/100579