[llvm] 777c320 - [VPlan] Address comments missed in #142309.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2025-08-06T11:52:08+01:00
New Revision: 777c320e6c96e2de9d4c6dc52d6a85a5ef3b8569

URL: https://github.com/llvm/llvm-project/commit/777c320e6c96e2de9d4c6dc52d6a85a5ef3b8569
DIFF: https://github.com/llvm/llvm-project/commit/777c320e6c96e2de9d4c6dc52d6a85a5ef3b8569.diff

LOG: [VPlan] Address comments missed in #142309.

Address additional comments from
https://github.com/llvm/llvm-project/pull/142309.

Added: 
    

Modified: 
    llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
    llvm/lib/Transforms/Vectorize/VPlanTransforms.h

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index a52aa8420b301..307b5cf1a2c50 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -10321,8 +10321,9 @@ bool LoopVectorizePass::processLoop(Loop *L) {
 
       // TODO: Move to general VPlan pipeline once epilogue loops are also
       // supported.
-      VPlanTransforms::runPass(VPlanTransforms::materializeVectorTripCount,
-                               BestPlan, VF.Width, IC, PSE);
+      VPlanTransforms::runPass(
+          VPlanTransforms::materializeConstantVectorTripCount, BestPlan,
+          VF.Width, IC, PSE);
 
       LVP.executePlan(VF.Width, IC, BestPlan, Unroller, DT, false);
 
@@ -10393,8 +10394,9 @@ bool LoopVectorizePass::processLoop(Loop *L) {
                                Checks, BestPlan);
         // TODO: Move to general VPlan pipeline once epilogue loops are also
         // supported.
-        VPlanTransforms::runPass(VPlanTransforms::materializeVectorTripCount,
-                                 BestPlan, VF.Width, IC, PSE);
+        VPlanTransforms::runPass(
+            VPlanTransforms::materializeConstantVectorTripCount, BestPlan,
+            VF.Width, IC, PSE);
 
         LVP.executePlan(VF.Width, IC, BestPlan, LB, DT, false);
         ++LoopsVectorized;

diff  --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index a7965a053e6e3..57f8e32029cbf 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -3222,7 +3222,7 @@ void VPlanTransforms::materializeBroadcasts(VPlan &Plan) {
   }
 }
 
-void VPlanTransforms::materializeVectorTripCount(
+void VPlanTransforms::materializeConstantVectorTripCount(
     VPlan &Plan, ElementCount BestVF, unsigned BestUF,
     PredicatedScalarEvolution &PSE) {
   assert(Plan.hasVF(BestVF) && "BestVF is not available in Plan");
@@ -3230,19 +3230,26 @@ void VPlanTransforms::materializeVectorTripCount(
 
   VPValue *TC = Plan.getTripCount();
   // Skip cases for which the trip count may be non-trivial to materialize.
+  // I.e., when a scalar tail is absent - due to tail folding, or when a scalar
+  // tail is required.
   if (!Plan.hasScalarTail() ||
       Plan.getMiddleBlock()->getSingleSuccessor() ==
           Plan.getScalarPreheader() ||
       !TC->isLiveIn())
     return;
+
   // Materialize vector trip counts for constants early if it can simply
   // be computed as (Original TC / VF * UF) * VF * UF.
+  // TODO: Compute vector trip counts for loops requiring a scalar epilogue and
+  // tail-folded loops.
   ScalarEvolution &SE = *PSE.getSE();
   auto *TCScev = SE.getSCEV(TC->getLiveInIRValue());
+  if (!isa<SCEVConstant>(TCScev))
+    return;
   const SCEV *VFxUF = SE.getElementCount(TCScev->getType(), BestVF * BestUF);
   auto VecTCScev = SE.getMulExpr(SE.getUDivExpr(TCScev, VFxUF), VFxUF);
-  if (auto *NewC = dyn_cast<SCEVConstant>(VecTCScev))
-    Plan.getVectorTripCount().setUnderlyingValue(NewC->getValue());
+  if (auto *ConstVecTC = dyn_cast<SCEVConstant>(VecTCScev))
+    Plan.getVectorTripCount().setUnderlyingValue(ConstVecTC->getValue());
 }
 
 void VPlanTransforms::materializeBackedgeTakenCount(VPlan &Plan,

diff  --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.h b/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
index 5943684e17a76..ecaca72e8e7ed 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
@@ -252,9 +252,10 @@ struct VPlanTransforms {
 
   // Materialize vector trip counts for constants early if it can simply be
   // computed as (Original TC / VF * UF) * VF * UF.
-  static void materializeVectorTripCount(VPlan &Plan, ElementCount BestVF,
-                                         unsigned BestUF,
-                                         PredicatedScalarEvolution &PSE);
+  static void
+  materializeConstantVectorTripCount(VPlan &Plan, ElementCount BestVF,
+                                     unsigned BestUF,
+                                     PredicatedScalarEvolution &PSE);
 
   /// Materialize the backedge-taken count to be computed explicitly using
   /// VPInstructions.