[SLP] Fix insert point for reused extract instructions.

[ABataev]

Summary

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.

[efriedma]

This version makes a lot more sense. :)

lib/Transforms/Vectorize/SLPVectorizer.cpp

3112

Please add a test for the case where NeedToShuffleReuses is true and E->ReorderIndices.empty() is false.

[ABataev]

lib/Transforms/Vectorize/SLPVectorizer.cpp

3112

We already have that kind of test X86/vectorize-reorder-reuse.ll, but I'll add another one.

[ABataev]

Added an extra test.

[efriedma]

LGTM

lib/Transforms/Vectorize/SLPVectorizer.cpp

case Instruction::ExtractElement: {
           OrdersType Mask;
           inversePermutation(E->ReorderIndices, Mask);
           Builder.SetInsertPoint(VL0);
           V = Builder.CreateShuffleVector(V, UndefValue::get(VecTy), Mask,
                                           "reorder_shuffle");
         }
         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");
         }
         E->VectorizedValue = V;
         return V;
       }
       setInsertPointAfterBundle(E->Scalars, S);
       auto *V = Gather(E->Scalars, VecTy);

test/Transforms/SLPVectorizer/AArch64/PR38339.ll

;
   %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
   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
+}