[PATCH] D49928: [SLP] Fix PR38339: Instruction does not dominate all uses!

[Alexey Bataev via Phabricator via llvm-commits]

ABataev created this revision.
ABataev added reviewers: spatel, RKSimon, mkuper, hfinkel.
Herald added a reviewer: javed.absar.

If the ExtractElement instructions can be optimized out during the
vectorization and we need to reshuffle the parent vector, this
ShuffleInstruction may be inserted in the wrong place causing compiler
to produce incorrect code.


Repository:
  rL LLVM

https://reviews.llvm.org/D49928

Files:
  lib/Transforms/Vectorize/SLPVectorizer.cpp
  test/Transforms/SLPVectorizer/AArch64/PR38339.ll


Index: test/Transforms/SLPVectorizer/AArch64/PR38339.ll
===================================================================
--- /dev/null
+++ test/Transforms/SLPVectorizer/AArch64/PR38339.ll
@@ -0,0 +1,48 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -slp-vectorizer -S -mtriple=aarch64-apple-ios -mcpu=cyclone -o - %s | FileCheck %s
+
+ at a = dso_local global i16 0, align 2
+
+define void @f1() {
+; CHECK-LABEL: @f1(
+; CHECK-NEXT:    [[TMP1:%.*]] = ptrtoint <2 x i16*> undef to <2 x i16>
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x i16> [[TMP1]], <2 x i16> undef, <4 x i32> <i32 0, i32 1, i32 1, i32 0>
+; CHECK-NEXT:    [[PTR0:%.*]] = getelementptr inbounds [4 x i16], [4 x i16]* undef, i16 0, i16 0
+; CHECK-NEXT:    [[PTR1:%.*]] = getelementptr inbounds [4 x i16], [4 x i16]* undef, i16 0, i16 1
+; CHECK-NEXT:    [[PTR2:%.*]] = getelementptr inbounds [4 x i16], [4 x i16]* undef, i16 0, i16 2
+; CHECK-NEXT:    [[PTR3:%.*]] = getelementptr inbounds [4 x i16], [4 x i16]* undef, i16 0, i16 3
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    br i1 undef, label [[BB3:%.*]], label [[BB2:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <4 x i16> [[SHUFFLE]], i32 0
+; CHECK-NEXT:    store i16 [[TMP2]], i16* @a, align 2
+; CHECK-NEXT:    [[TMP3:%.*]] = bitcast i16* [[PTR0]] to <4 x i16>*
+; CHECK-NEXT:    store <4 x i16> [[SHUFFLE]], <4 x i16>* [[TMP3]], align 2
+; CHECK-NEXT:    br label [[BB1]]
+; CHECK:       bb3:
+; CHECK-NEXT:    ret void
+;
+  %1 = ptrtoint <2 x i16*> undef to <2 x i16>
+  %2 = extractelement <2 x i16> %1, i32 0
+  %3 = extractelement <2 x i16> %1, i32 1
+  %ptr0 = getelementptr inbounds [4 x i16], [4 x i16]* undef, i16 0, i16 0
+  %ptr1 = getelementptr inbounds [4 x i16], [4 x i16]* undef, i16 0, i16 1
+  %ptr2 = getelementptr inbounds [4 x i16], [4 x i16]* undef, i16 0, i16 2
+  %ptr3 = getelementptr inbounds [4 x i16], [4 x i16]* undef, i16 0, i16 3
+  br label %bb1
+
+bb1:                                              ; preds = %bb2, %0
+  br i1 undef, label %bb3, label %bb2
+
+bb2:                                              ; preds = %bb1
+  store i16 %2, i16* @a,    align 2
+  store i16 %2, i16* %ptr0, align 2
+  store i16 %3, i16* %ptr1, align 2
+  store i16 %3, i16* %ptr2, align 2
+  store i16 %2, i16* %ptr3, align 2
+  br label %bb1
+
+bb3:                                              ; preds = %bb1
+  ret void
+}
Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -3111,6 +3111,12 @@
           // TODO: Merge this shuffle with the ReorderShuffleMask.
           if (!E->ReorderIndices.empty())
             Builder.SetInsertPoint(VL0);
+          else if (auto *I = dyn_cast<Instruction>(V))
+            Builder.SetInsertPoint(I->getParent(),
+                                   std::next(I->getIterator()));
+          else
+            Builder.SetInsertPoint(&F->getEntryBlock(),
+                                   F->getEntryBlock().getFirstInsertionPt());
           V = Builder.CreateShuffleVector(V, UndefValue::get(VecTy),
                                           E->ReuseShuffleIndices, "shuffle");
         }


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