Bad SLPVectorization shufflevector replacement, resulting in write to wrong memory location

We see that it might otherwise do:

  %10 = getelementptr {}**, <2 x {}***> %9, <2 x i32> <i32 10, i32 4>
  %11 = bitcast <2 x {}***> %10 to <2 x i64*>
...
  %27 = extractelement <2 x i64*> %11, i32 0
  %28 = bitcast i64* %27 to <2 x i64>*
  store <2 x i64> %22, <2 x i64>* %28, align 4, !tbaa !2

Which is an out-of-bounds store (the extractelement got offset 10
instead of offset 4 as intended). With the fix, we correctly generate
extractelement for i32 1 and generate correct code.

Differential Revision: https://reviews.llvm.org/D106613

(cherry picked from commit e27a6db)

Author: vtjnash

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -5430,8 +5430,11 @@ Value *BoUpSLP::vectorizeTree(TreeEntry *E) {
         // The pointer operand uses an in-tree scalar so we add the new BitCast
         // to ExternalUses list to make sure that an extract will be generated
         // in the future.
-        if (getTreeEntry(PO))
-          ExternalUses.emplace_back(PO, cast<User>(VecPtr), 0);
+        if (TreeEntry *Entry = getTreeEntry(PO)) {
+          // Find which lane we need to extract.
+          unsigned FoundLane = Entry->findLaneForValue(PO);
+          ExternalUses.emplace_back(PO, cast<User>(VecPtr), FoundLane);
+        }
 
         NewLI = Builder.CreateAlignedLoad(VecTy, VecPtr, LI->getAlign());
       } else {
@@ -5474,8 +5477,12 @@ Value *BoUpSLP::vectorizeTree(TreeEntry *E) {
       // The pointer operand uses an in-tree scalar, so add the new BitCast to
       // ExternalUses to make sure that an extract will be generated in the
       // future.
-      if (getTreeEntry(ScalarPtr))
-        ExternalUses.push_back(ExternalUser(ScalarPtr, cast<User>(VecPtr), 0));
+      if (TreeEntry *Entry = getTreeEntry(ScalarPtr)) {
+        // Find which lane we need to extract.
+        unsigned FoundLane = Entry->findLaneForValue(ScalarPtr);
+        ExternalUses.push_back(
+            ExternalUser(ScalarPtr, cast<User>(VecPtr), FoundLane));
+      }
 
       Value *V = propagateMetadata(ST, E->Scalars);
 
@@ -5577,8 +5584,14 @@ Value *BoUpSLP::vectorizeTree(TreeEntry *E) {
       // The scalar argument uses an in-tree scalar so we add the new vectorized
       // call to ExternalUses list to make sure that an extract will be
       // generated in the future.
-      if (ScalarArg && getTreeEntry(ScalarArg))
-        ExternalUses.push_back(ExternalUser(ScalarArg, cast<User>(V), 0));
+      if (ScalarArg) {
+        if (TreeEntry *Entry = getTreeEntry(ScalarArg)) {
+          // Find which lane we need to extract.
+          unsigned FoundLane = Entry->findLaneForValue(ScalarArg);
+          ExternalUses.push_back(
+              ExternalUser(ScalarArg, cast<User>(V), FoundLane));
+        }
+      }
 
       propagateIRFlags(V, E->Scalars, VL0);
       ShuffleBuilder.addMask(E->ReuseShuffleIndices);

llvm/test/Transforms/SLPVectorizer/X86/extract_in_tree_user.ll

@@ -108,10 +108,9 @@ define void @externally_used_ptrs() {
 ; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr i64, <2 x i64*> [[TMP2]], <2 x i64> <i64 56, i64 11>
 ; CHECK-NEXT:    [[TMP4:%.*]] = ptrtoint <2 x i64*> [[TMP3]] to <2 x i64>
 ; CHECK-NEXT:    [[ARRAYIDX2:%.*]] = getelementptr inbounds i64, i64* [[TMP0]], i64 12
-; CHECK-NEXT:    [[TMP5:%.*]] = extractelement <2 x i64*> [[TMP3]], i32 0
+; CHECK-NEXT:    [[TMP5:%.*]] = extractelement <2 x i64*> [[TMP3]], i32 1
 ; CHECK-NEXT:    [[TMP6:%.*]] = bitcast i64* [[TMP5]] to <2 x i64>*
 ; CHECK-NEXT:    [[TMP7:%.*]] = load <2 x i64>, <2 x i64>* [[TMP6]], align 8
-; CHECK-NEXT:    [[TMP8:%.*]] = extractelement <2 x i64*> [[TMP3]], i32 1
 ; CHECK-NEXT:    [[TMP9:%.*]] = add <2 x i64> [[TMP4]], [[TMP7]]
 ; CHECK-NEXT:    [[TMP10:%.*]] = bitcast i64* [[TMP5]] to <2 x i64>*
 ; CHECK-NEXT:    store <2 x i64> [[TMP9]], <2 x i64>* [[TMP10]], align 8