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

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 506715.
fhahn added a comment.

Thanks for taking a look! I think it would be good to land this together with a concrete use of the new functionality, which would be D142886 <https://reviews.llvm.org/D142886> (still needing review :))


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D142885/new/

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
@@ -7555,6 +7555,12 @@
       LLVM_DEBUG(dbgs() << "LV: Using user VF " << UserVF << ".\n");
       CM.collectInLoopReductions();
       buildVPlansWithVPRecipes(UserVF, UserVF);
+      if (!hasPlanWithVF(UserVF)) {
+        LLVM_DEBUG(dbgs() << "LV: No VPlan could be built for " << UserVF
+                          << ".\n");
+        return std::nullopt;
+      }
+
       LLVM_DEBUG(printPlans(dbgs()));
       return {{UserVF, 0, 0}};
     } else
@@ -7592,6 +7598,11 @@
   // 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)) {
+    LLVM_DEBUG(dbgs() << "LV: No VPlan could be built for " << VF.Width
+                      << ".\n");
+    return std::nullopt;
+  }
   return VF;
 }
 
@@ -8668,7 +8679,8 @@
   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;
   }
 }
@@ -8799,7 +8811,7 @@
   }
 }
 
-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 +350,11 @@
 
   /// Build a VPlan using VPRecipes according to the information gather by
   /// Legal. This method is only used for the legacy inner loop vectorizer.
-  VPlanPtr
+  /// \p Range's largest included VF is restricted to the maximum VF the
+  /// returned VPlan is valid for. If no VPlan can be built for the input range,
+  /// set the largest included VF to the maximum VF for which no plan could be
+  /// built.
+  std::optional<VPlanPtr>
   buildVPlanWithVPRecipes(VFRange &Range,
                           SmallPtrSetImpl<Instruction *> &DeadInstructions);
 


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