[PATCH] D147963: [LV] Use VPValue for SCEV expansion in fixupIVUsers (NFCI).

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 514248.
fhahn added a comment.

Added test case that shows this patch is not an NFC. It fixes a crash casued by SCEV-expanding the Step expression in fixupIVUsers, where the IR is in an incomplete state. I will adjust the title accordingly.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D147963/new/

https://reviews.llvm.org/D147963

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/test/Transforms/LoopVectorize/pr58811-scev-expansion.ll


Index: llvm/test/Transforms/LoopVectorize/pr58811-scev-expansion.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/pr58811-scev-expansion.ll
+++ llvm/test/Transforms/LoopVectorize/pr58811-scev-expansion.ll
@@ -1,9 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -passes=loop-vectorize -force-vector-width=4 -force-vector-interleave=1 -S %s | FileCheck %s
 
-; REQUIRES: asserts
-; XFAIL: *
-
 define void @test1_pr58811() {
 ; CHECK-LABEL: @test1_pr58811(
 ; CHECK-NEXT:  entry:
Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -580,7 +580,7 @@
   void fixupIVUsers(PHINode *OrigPhi, const InductionDescriptor &II,
                     Value *VectorTripCount, Value *EndValue,
                     BasicBlock *MiddleBlock, BasicBlock *VectorHeader,
-                    VPlan &Plan);
+                    VPlan &Plan, VPTransformState &State);
 
   /// Handle all cross-iteration phis in the header.
   void fixCrossIterationPHIs(VPTransformState &State);
@@ -3370,7 +3370,8 @@
                                        const InductionDescriptor &II,
                                        Value *VectorTripCount, Value *EndValue,
                                        BasicBlock *MiddleBlock,
-                                       BasicBlock *VectorHeader, VPlan &Plan) {
+                                       BasicBlock *VectorHeader, VPlan &Plan,
+                                       VPTransformState &State) {
   // There are two kinds of external IV usages - those that use the value
   // computed in the last iteration (the PHI) and those that use the penultimate
   // value (the value that feeds into the phi from the loop latch).
@@ -3394,11 +3395,35 @@
   // An external user of the penultimate value need to see EndValue - Step.
   // The simplest way to get this is to recompute it from the constituent SCEVs,
   // that is Start + (Step * (CRD - 1)).
+  Value *Step = nullptr;
   for (User *U : OrigPhi->users()) {
     auto *UI = cast<Instruction>(U);
     if (!OrigLoop->contains(UI)) {
       assert(isa<PHINode>(UI) && "Expected LCSSA form");
 
+      if (!Step) {
+        // Get the value corresponding to the expansion of the induction step.
+        // First try to directly convert the SCEV, otherwise look for a
+        // corresponding VPExpandSCEVRecipe.
+        if (auto *S = dyn_cast<SCEVConstant>(II.getStep()))
+          Step = S->getValue();
+        else if (auto *S = dyn_cast<SCEVUnknown>(II.getStep()))
+          Step = S->getValue();
+        else {
+          // All steps for induction should have been expanded earlier, so this
+          // only looks up existing VPValues.
+          VPBasicBlock *Preheader = Plan.getEntry()->getEntryBasicBlock();
+          for (auto &R : *Preheader) {
+            auto *StepR = dyn_cast<VPExpandSCEVRecipe>(&R);
+            if (StepR && StepR->getSCEV() == II.getStep()) {
+              Step = State.get(StepR, 0);
+              break;
+            }
+          }
+          assert(Step && "need a step here");
+        }
+      }
+
       IRBuilder<> B(MiddleBlock->getTerminator());
 
       // Fast-math-flags propagate from the original induction instruction.
@@ -3408,8 +3433,7 @@
       Value *CountMinusOne = B.CreateSub(
           VectorTripCount, ConstantInt::get(VectorTripCount->getType(), 1));
       CountMinusOne->setName("cmo");
-      Value *Step = CreateStepValue(II.getStep(), *PSE.getSE(),
-                                    VectorHeader->getTerminator());
+
       Value *Escape =
           emitTransformedIndex(B, CountMinusOne, II.getStartValue(), Step, II);
       Escape->setName("ind.escape");
@@ -3768,7 +3792,7 @@
       fixupIVUsers(Entry.first, Entry.second,
                    getOrCreateVectorTripCount(VectorLoop->getLoopPreheader()),
                    IVEndValues[Entry.first], LoopMiddleBlock,
-                   VectorLoop->getHeader(), Plan);
+                   VectorLoop->getHeader(), Plan, State);
   }
 
   // Fix LCSSA phis not already fixed earlier. Extracts may need to be generated


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