[PATCH] D103479: [SLP] Ignore unreachable blocks

[Harald van Dijk via Phabricator via llvm-commits]

hvdijk created this revision.
hvdijk added reviewers: ABataev, RKSimon.
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As the existing test unreachable.ll shows, we should be doing more
work to avoid entering unreachable blocks: we should not stop
vectorization just because a PHI incoming value from an unreachable
block cannot be vectorized. We know that particular value will never
be used so we can just replace it with poison.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D103479

Files:
  llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
  llvm/test/Transforms/SLPVectorizer/X86/unreachable.ll


Index: llvm/test/Transforms/SLPVectorizer/X86/unreachable.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/X86/unreachable.ll
+++ llvm/test/Transforms/SLPVectorizer/X86/unreachable.ll
@@ -23,17 +23,12 @@
 ; CHECK-NEXT:    [[T10:%.*]] = load i32, i32* [[T9]], align 4
 ; CHECK-NEXT:    br label [[BB2]]
 ; CHECK:       bb2:
-; CHECK-NEXT:    [[T1_0:%.*]] = phi i32 [ [[T4]], [[BB1:%.*]] ], [ 2, [[ENTRY:%.*]] ]
-; CHECK-NEXT:    [[T2_0:%.*]] = phi i32 [ [[T6]], [[BB1]] ], [ 2, [[ENTRY]] ]
-; CHECK-NEXT:    [[T3_0:%.*]] = phi i32 [ [[T8]], [[BB1]] ], [ 2, [[ENTRY]] ]
-; CHECK-NEXT:    [[T4_0:%.*]] = phi i32 [ [[T10]], [[BB1]] ], [ 2, [[ENTRY]] ]
-; CHECK-NEXT:    store i32 [[T1_0]], i32* [[X]], align 4
+; CHECK-NEXT:    [[TMP0:%.*]] = phi <4 x i32> [ poison, [[BB1:%.*]] ], [ <i32 2, i32 2, i32 2, i32 2>, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[T12:%.*]] = getelementptr inbounds i32, i32* [[X]], i64 1
-; CHECK-NEXT:    store i32 [[T2_0]], i32* [[T12]], align 4
 ; CHECK-NEXT:    [[T13:%.*]] = getelementptr inbounds i32, i32* [[X]], i64 2
-; CHECK-NEXT:    store i32 [[T3_0]], i32* [[T13]], align 4
 ; CHECK-NEXT:    [[T14:%.*]] = getelementptr inbounds i32, i32* [[X]], i64 3
-; CHECK-NEXT:    store i32 [[T4_0]], i32* [[T14]], align 4
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i32* [[X]] to <4 x i32>*
+; CHECK-NEXT:    store <4 x i32> [[TMP0]], <4 x i32>* [[TMP1]], align 4
 ; CHECK-NEXT:    ret void
 ;
 entry:
Index: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -2830,6 +2830,8 @@
       // Keeps the reordered operands to avoid code duplication.
       SmallVector<ValueList, 2> OperandsVec;
       for (unsigned I = 0, E = PH->getNumIncomingValues(); I < E; ++I) {
+        if (!DT->isReachableFromEntry(PH->getIncomingBlock(I)))
+          continue;
         ValueList Operands;
         // Prepare the operand vector.
         for (Value *V : VL)
@@ -4921,6 +4923,11 @@
         ValueList Operands;
         BasicBlock *IBB = PH->getIncomingBlock(i);
 
+        if (!DT->isReachableFromEntry(IBB)) {
+          NewPhi->addIncoming(PoisonValue::get(NewPhi->getType()), IBB);
+          continue;
+        }
+
         if (!VisitedBBs.insert(IBB).second) {
           NewPhi->addIncoming(NewPhi->getIncomingValueForBlock(IBB), IBB);
           continue;


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