From 37f68c77b2bd7c8387b01d7fce4398f0bef5ec67 Mon Sep 17 00:00:00 2001
From: Jameson Nash <vtjnash@gmail.com>
Date: Thu, 22 Jul 2021 19:42:23 -0400
Subject: [PATCH] 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 980d2f60a8524c5546397db9e8bbb7d6ea56c1b7)
---
 .../Transforms/Vectorize/SLPVectorizer.cpp    | 25 ++++++++++----
 .../SLPVectorizer/X86/extract_in_tree_user.ll | 33 +++++++++++++++++++
 2 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index cc3f5c7d4b481e..1d06bc7d79a7e8 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/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);
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/extract_in_tree_user.ll b/llvm/test/Transforms/SLPVectorizer/X86/extract_in_tree_user.ll
index efbdb14ddb8a1f..d4cb77884f6504 100644
--- a/llvm/test/Transforms/SLPVectorizer/X86/extract_in_tree_user.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/extract_in_tree_user.ll
@@ -99,3 +99,36 @@ entry:
   ret void
 
 }
+
+define void @externally_used_ptrs() {
+; CHECK-LABEL: @externally_used_ptrs(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = load i64*, i64** @a, align 8
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <2 x i64*> poison, i64* [[TMP0]], i32 0
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <2 x i64*> [[TMP1]], i64* [[TMP0]], i32 1
+; 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 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:%.*]] = add <2 x i64> [[TMP4]], [[TMP7]]
+; CHECK-NEXT:    [[TMP9:%.*]] = bitcast i64* [[TMP5]] to <2 x i64>*
+; CHECK-NEXT:    store <2 x i64> [[TMP8]], <2 x i64>* [[TMP9]], align 8
+; CHECK-NEXT:    ret void
+;
+entry:
+  %0 = load i64*, i64** @a, align 8
+  %add.ptr = getelementptr inbounds i64, i64* %0, i64 11
+  %1 = ptrtoint i64* %add.ptr to i64
+  %add.ptr1 = getelementptr inbounds i64, i64* %0, i64 56
+  %2 = ptrtoint i64* %add.ptr1 to i64
+  %arrayidx2 = getelementptr inbounds i64, i64* %0, i64 12
+  %3 = load i64, i64* %arrayidx2, align 8
+  %4 = load i64, i64* %add.ptr, align 8
+  %5 = add i64 %1, %3
+  %6 = add i64 %2, %4
+  store i64 %6, i64* %add.ptr, align 8
+  store i64 %5, i64* %arrayidx2, align 8
+  ret void
+}