[PATCH] D50143: [SLP] Fix insert point for reused extract instructions.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev created this revision.
ABataev added a reviewer: efriedma.
Herald added a reviewer: javed.absar.

Reworked the previously committed patch to insert shuffles for reused
extract element instructions in the correct position. Previous logic was
incorrect, and might lead to the crash with PHIs and EH instructions.


Repository:
  rL LLVM

https://reviews.llvm.org/D50143

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


Index: test/Transforms/SLPVectorizer/AArch64/PR38339.ll
===================================================================
--- test/Transforms/SLPVectorizer/AArch64/PR38339.ll
+++ test/Transforms/SLPVectorizer/AArch64/PR38339.ll
@@ -27,3 +27,50 @@
   store i16 %t2, i16* %ptr3
   ret void
 }
+
+define void @f2(<2 x i16> %x, i16* %a) {
+; CHECK-LABEL: @f2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[CONT:%.*]]
+; CHECK:       cont:
+; CHECK-NEXT:    [[XX:%.*]] = phi <2 x i16> [ [[X:%.*]], [[ENTRY:%.*]] ], [ undef, [[CONT]] ]
+; CHECK-NEXT:    [[AA:%.*]] = phi i16* [ [[A:%.*]], [[ENTRY]] ], [ undef, [[CONT]] ]
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x i16> [[XX]], <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:    [[TMP0:%.*]] = extractelement <4 x i16> [[SHUFFLE]], i32 0
+; CHECK-NEXT:    store i16 [[TMP0]], i16* [[A]]
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i16* [[PTR0]] to <4 x i16>*
+; CHECK-NEXT:    store <4 x i16> [[SHUFFLE]], <4 x i16>* [[TMP1]], align 2
+; CHECK-NEXT:    [[A_VAL:%.*]] = load i16, i16* [[A]], align 2
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 [[A_VAL]], 0
+; CHECK-NEXT:    br i1 [[CMP]], label [[CONT]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %cont
+
+cont:                                           ; preds = %entry, %cont
+  %xx = phi <2 x i16> [ %x, %entry ], [ undef, %cont ]
+  %aa = phi i16* [ %a, %entry ], [ undef, %cont ]
+  %t2 = extractelement <2 x i16> %xx, i32 0
+  %t3 = extractelement <2 x i16> %xx, 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
+  store i16 %t2, i16* %a
+  store i16 %t2, i16* %ptr0
+  store i16 %t3, i16* %ptr1
+  store i16 %t3, i16* %ptr2
+  store i16 %t2, i16* %ptr3
+  %a_val = load i16, i16* %a, align 2
+  %cmp = icmp eq i16 %a_val, 0
+  br i1 %cmp, label %cont, label %exit
+
+exit:                                           ; preds = %cont
+  ret void
+}
Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -3109,14 +3109,8 @@
         }
         if (NeedToShuffleReuses) {
           // TODO: Merge this shuffle with the ReorderShuffleMask.
-          if (!E->ReorderIndices.empty())
+          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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