From 2bcc4db761768f1b7431237920f26360549ca268 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo@fhahn.com>
Date: Wed, 9 Sep 2020 09:00:41 +0100
Subject: [PATCH] [EarlyCSE] Explicitly require AAResultsWrapperPass.

The MemorySSAWrapperPass depends on AAResultsWrapperPass and if
MemorySSA is preserved but AAResultsWrapperPass is not, this could lead
to a crash when updating the last user of the MemorySSAWrapperPass.

Alternatively AAResultsWrapperPass could be marked preserved by GVN, but
I am not sure if that would be safe. I am not sure what is required in
order to preserve AAResultsWrapperPass. At the moment, it seems like a
couple of passes that do similar transforms to GVN are preserving it.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D87137
---
 llvm/lib/Transforms/Scalar/EarlyCSE.cpp                    | 2 ++
 llvm/lib/Transforms/Scalar/GVN.cpp                         | 1 -
 llvm/test/Transforms/EarlyCSE/reuse-preserved-memoryssa.ll | 7 +++++++
 3 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Transforms/EarlyCSE/reuse-preserved-memoryssa.ll

diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index 51da10fc4879..b655204d26dd 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -1463,6 +1463,7 @@ public:
     AU.addRequired<TargetLibraryInfoWrapperPass>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
     if (UseMemorySSA) {
+      AU.addRequired<AAResultsWrapperPass>();
       AU.addRequired<MemorySSAWrapperPass>();
       AU.addPreserved<MemorySSAWrapperPass>();
     }
@@ -1504,6 +1505,7 @@ INITIALIZE_PASS_BEGIN(EarlyCSEMemSSALegacyPass, "early-cse-memssa",
                       "Early CSE w/ MemorySSA", false, false)
 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index c71038d66f99..036ca1d1054f 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -2850,7 +2850,6 @@ public:
     if (Impl.isMemDepEnabled())
       AU.addRequired<MemoryDependenceWrapperPass>();
     AU.addRequired<AAResultsWrapperPass>();
-
     AU.addPreserved<DominatorTreeWrapperPass>();
     AU.addPreserved<GlobalsAAWrapperPass>();
     AU.addPreserved<TargetLibraryInfoWrapperPass>();
diff --git a/llvm/test/Transforms/EarlyCSE/reuse-preserved-memoryssa.ll b/llvm/test/Transforms/EarlyCSE/reuse-preserved-memoryssa.ll
new file mode 100644
index 000000000000..744389c24db2
--- /dev/null
+++ b/llvm/test/Transforms/EarlyCSE/reuse-preserved-memoryssa.ll
@@ -0,0 +1,7 @@
+; RUN: opt -memoryssa -gvn -early-cse-memssa %s -S | FileCheck %s
+
+; CHECK: define void @foo(
+
+define void @foo() {
+  ret void
+}