[PATCH] D142885: [VPlan] Allow building a VPlan to may fail.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: Ayal, gilr, rengolin.
Herald added subscribers: StephenFan, tschuett, psnobl, rogfer01, bollu, hiraditya.
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Update the planning code constructing VPlan to allow building VPlans to
fail. This allows us to gradually shift some legality checks to VPlan
construction. The first candidate is checking if all users of
first-order recurrence phis can be sunk past the recipe computing the
previous value.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D142885

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
  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
@@ -7528,6 +7528,9 @@
       CM.collectInLoopReductions();
       buildVPlansWithVPRecipes(UserVF, UserVF);
       LLVM_DEBUG(printPlans(dbgs()));
+      if (!hasPlanWithVF(UserVF))
+        return std::nullopt;
+
       return {{UserVF, 0, 0}};
     } else
       reportVectorizationInfo("UserVF ignored because of invalid costs.",
@@ -7564,6 +7567,8 @@
   // Select the optimal vectorization factor.
   VectorizationFactor VF = CM.selectVectorizationFactor(VFCandidates);
   assert((VF.Width.isScalar() || VF.ScalarCost > 0) && "when vectorizing, the scalar cost must be non-zero.");
+  if (!hasPlanWithVF(VF.Width))
+    return std::nullopt;
   return VF;
 }
 
@@ -8680,7 +8685,8 @@
   auto MaxVFPlusOne = MaxVF.getWithIncrement(1);
   for (ElementCount VF = MinVF; ElementCount::isKnownLT(VF, MaxVFPlusOne);) {
     VFRange SubRange = {VF, MaxVFPlusOne};
-    VPlans.push_back(buildVPlanWithVPRecipes(SubRange, DeadInstructions));
+    if (auto Plan = buildVPlanWithVPRecipes(SubRange, DeadInstructions))
+      VPlans.push_back(std::move(*Plan));
     VF = SubRange.End;
   }
 }
@@ -8785,7 +8791,7 @@
   }
 }
 
-VPlanPtr LoopVectorizationPlanner::buildVPlanWithVPRecipes(
+std::optional<VPlanPtr> LoopVectorizationPlanner::buildVPlanWithVPRecipes(
     VFRange &Range, SmallPtrSetImpl<Instruction *> &DeadInstructions) {
 
   SmallPtrSet<const InterleaveGroup<Instruction> *, 1> InterleaveGroups;
Index: llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
+++ llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
@@ -350,7 +350,7 @@
 
   /// Build a VPlan using VPRecipes according to the information gather by
   /// Legal. This method is only used for the legacy inner loop vectorizer.
-  VPlanPtr
+  std::optional<VPlanPtr>
   buildVPlanWithVPRecipes(VFRange &Range,
                           SmallPtrSetImpl<Instruction *> &DeadInstructions);
 


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