[PATCH] D99294: [LV] Track incoming values for reductions in recipe (NFC).

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: gilr, Ayal, rengolin.
Herald added subscribers: rogfer01, bollu, hiraditya.
fhahn requested review of this revision.
Herald added a subscriber: vkmr.
Herald added a project: LLVM.

This patch updates the code handling reduction recipes to also keep
track of the incoming value from the latch in the recipe. This is needed
to model the def-use chains completely in VPlan, so that it is possible
to replace the incoming value with an arbitrary VPValue.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D99294

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp


Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4259,14 +4259,11 @@
 
   // Reductions do not have to start at zero. They can start with
   // any loop invariant values.
-  BasicBlock *Latch = OrigLoop->getLoopLatch();
-  Value *LoopVal = OrigPhi->getIncomingValueForBlock(Latch);
-
   for (unsigned Part = 0; Part < UF; ++Part) {
-    Value *VecRdxPhi = State.get(PhiR->getVPValue(), Part);
-    Value *Val = State.get(State.Plan->getVPValue(LoopVal), Part);
-    cast<PHINode>(VecRdxPhi)
-      ->addIncoming(Val, LI->getLoopFor(LoopVectorBody)->getLoopLatch());
+    Value *VecRdxPhi = State.get(PhiR->getVPValue(0), Part);
+    cast<PHINode>(VecRdxPhi)->addIncoming(
+        State.get(PhiR->getOperand(1), Part),
+        LI->getLoopFor(LoopVectorBody)->getLoopLatch());
   }
 
   // Before each round, move the insertion point right between
@@ -8746,6 +8743,18 @@
     RecipeBuilder.recordRecipeOf(Entry.first);
     RecipeBuilder.recordRecipeOf(Entry.second);
   }
+
+  SmallVector<PHINode *, 4> PhisToFix;
+  BasicBlock *OrigLatch = OrigLoop->getLoopLatch();
+  for (PHINode &Phi : OrigLoop->getHeader()->phis()) {
+    if (!Legal->isReductionVariable(&Phi))
+      continue;
+    PhisToFix.push_back(&Phi);
+    RecipeBuilder.recordRecipeOf(&Phi);
+    RecipeBuilder.recordRecipeOf(
+        cast<Instruction>(Phi.getIncomingValueForBlock(OrigLatch)));
+  }
+
   for (auto &Reduction : CM.getInLoopReductionChains()) {
     PHINode *Phi = Reduction.first;
     RecurKind Kind = Legal->getReductionVars()[Phi].getRecurrenceKind();
@@ -8844,6 +8853,14 @@
     }
   }
 
+  for (PHINode *PN : PhisToFix) {
+    VPWidenPHIRecipe *R = cast<VPWidenPHIRecipe>(RecipeBuilder.getRecipe(PN));
+    VPRecipeBase *IncR = RecipeBuilder.getRecipe(
+        cast<Instruction>(PN->getIncomingValueForBlock(OrigLatch)));
+    assert(IncR->getNumDefinedValues() == 1);
+    R->addOperand(IncR->getVPValue(0));
+  }
+
   // Discard empty dummy pre-entry VPBasicBlock. Note that other VPBasicBlocks
   // may also be empty, such as the last one VPBB, reflecting original
   // basic-blocks with no recipes.


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