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

[Sander de Smalen via llvm-branch-commits]

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@@ -2030,32 +2031,68 @@ Value *llvm::addDiffRuntimeChecks(
   // Map to keep track of created compares, The key is the pair of operands for
   // the compare, to allow detecting and re-using redundant compares.
   DenseMap<std::pair<Value *, Value *>, Value *> SeenCompares;
-  for (const auto &[SrcStart, SinkStart, AccessSize, NeedsFreeze] : Checks) {
+  Value *AliasLaneMask = nullptr;
+  for (const auto &[SrcStart, SinkStart, AccessSize, NeedsFreeze,
+                    WriteAfterRead] : Checks) {
     Type *Ty = SinkStart->getType();
-    // Compute VF * IC * AccessSize.
-    auto *VFTimesICTimesSize =
-        ChkBuilder.CreateMul(GetVF(ChkBuilder, Ty->getScalarSizeInBits()),
-                             ConstantInt::get(Ty, IC * AccessSize));
-    Value *Diff =
-        Expander.expandCodeFor(SE.getMinusSCEV(SinkStart, SrcStart), Ty, Loc);
-
-    // Check if the same compare has already been created earlier. In that case,
-    // there is no need to check it again.
-    Value *IsConflict = SeenCompares.lookup({Diff, VFTimesICTimesSize});
-    if (IsConflict)
-      continue;
+    if (!VF.isScalar() && UseSafeEltsMask) {
+      Value *Sink = Expander.expandCodeFor(SinkStart, Ty, Loc);
+      Value *Src = Expander.expandCodeFor(SrcStart, Ty, Loc);
+      unsigned IntOpc = WriteAfterRead ? Intrinsic::loop_dependence_war_mask
+                                       : Intrinsic::loop_dependence_raw_mask;
+      Value *SourceAsPtr = ChkBuilder.CreateCast(Instruction::IntToPtr, Src,
+                                                 ChkBuilder.getPtrTy());
+      Value *SinkAsPtr = ChkBuilder.CreateCast(Instruction::IntToPtr, Sink,
+                                               ChkBuilder.getPtrTy());
+      Value *M = ChkBuilder.CreateIntrinsic(
+          IntOpc, {VectorType::get(ChkBuilder.getInt1Ty(), VF)},
+          {SourceAsPtr, SinkAsPtr, ChkBuilder.getInt64(AccessSize)}, nullptr,
+          "alias.lane.mask");
+      if (AliasLaneMask)
+        M = ChkBuilder.CreateAnd(AliasLaneMask, M);
+      else
+        AliasLaneMask = M;
+    } else {
+      // Compute VF * IC * AccessSize.
+      auto *VFTimesICTimesSize =
+          ChkBuilder.CreateMul(GetVF(ChkBuilder, Ty->getScalarSizeInBits()),
+                               ConstantInt::get(Ty, IC * AccessSize));
+      Value *Diff =
+          Expander.expandCodeFor(SE.getMinusSCEV(SinkStart, SrcStart), Ty, Loc);
+
+      // Check if the same compare has already been created earlier. In that
+      // case, there is no need to check it again.
+      Value *IsConflict = SeenCompares.lookup({Diff, VFTimesICTimesSize});
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sdesmalen-arm wrote:

Do you need to use/check `SeenCompares` in the loop_dependence_war/raw_mask path as well?

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