[SLPVectorizer] Ignore unreachable blocks

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.
syntacore · Jun 1, 2021 · f126e8e · f126e8e
1 parent 2020c98
commit f126e8e
Show file tree

Hide file tree

Showing 2 changed files with 9 additions and 8 deletions.
diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -2831,6 +2831,12 @@ void BoUpSLP::buildTree_rec(ArrayRef<Value *> VL, unsigned Depth,
       // 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))) {
+          ValueList Operands(VL.size(), PoisonValue::get(PH->getType()));
+          TE->setOperand(I, Operands);
+          OperandsVec.push_back(Operands);
+          continue;
+        }
         ValueList Operands;
         // Prepare the operand vector.
         for (Value *V : VL)

diff --git a/llvm/test/Transforms/SLPVectorizer/X86/unreachable.ll b/llvm/test/Transforms/SLPVectorizer/X86/unreachable.ll
@@ -23,17 +23,12 @@ define void @foo(i32* nocapture %x) #0 {
 ; 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: