[llvm] [PPCMergeStringPool] Only replace constant once (PR #92996)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Thu May 23 00:05:26 PDT 2024
https://github.com/nikic updated https://github.com/llvm/llvm-project/pull/92996
>From 870147d977f7bedccc4986992e5652227ddf4ffb Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Wed, 22 May 2024 08:39:50 +0200
Subject: [PATCH 1/3] [PPCMergeStringPool] Only replace constant once
In #88846 I changed this code to use RAUW to perform the replacement
instead of manual updates -- but kept the outer loop, which means
we try to perform RAUW once per user. However, some of the users
might be freed by the RAUW operation, resulting in use-after-free.
I think the case where this happens is constant users where the
replacement might result in the destruction of the original
constant. I wasn't able to come up with a test case though.
This is intended to fix https://github.com/llvm/llvm-project/issues/92991.
---
.../lib/Target/PowerPC/PPCMergeStringPool.cpp | 37 ++++---------------
1 file changed, 7 insertions(+), 30 deletions(-)
diff --git a/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp b/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
index abc5353e4a5e9..b73e25d37f8f5 100644
--- a/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
+++ b/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
@@ -302,13 +302,6 @@ bool PPCMergeStringPool::mergeModuleStringPool(Module &M) {
return true;
}
-static bool userHasOperand(User *TheUser, GlobalVariable *GVOperand) {
- for (Value *Op : TheUser->operands())
- if (Op == GVOperand)
- return true;
- return false;
-}
-
// For pooled strings we need to add the offset into the pool for each string.
// This is done by adding a Get Element Pointer (GEP) before each user. This
// function adds the GEP.
@@ -319,29 +312,13 @@ void PPCMergeStringPool::replaceUsesWithGEP(GlobalVariable *GlobalToReplace,
Indices.push_back(ConstantInt::get(Type::getInt32Ty(*Context), 0));
Indices.push_back(ConstantInt::get(Type::getInt32Ty(*Context), ElementIndex));
- // Need to save a temporary copy of each user list because we remove uses
- // as we replace them.
- SmallVector<User *> Users;
- for (User *CurrentUser : GlobalToReplace->users())
- Users.push_back(CurrentUser);
-
- for (User *CurrentUser : Users) {
- // The user was not found so it must have been replaced earlier.
- if (!userHasOperand(CurrentUser, GlobalToReplace))
- continue;
-
- // We cannot replace operands in globals so we ignore those.
- if (isa<GlobalValue>(CurrentUser))
- continue;
-
- Constant *ConstGEP = ConstantExpr::getInBoundsGetElementPtr(
- PooledStructType, GPool, Indices);
- LLVM_DEBUG(dbgs() << "Replacing this global:\n");
- LLVM_DEBUG(GlobalToReplace->dump());
- LLVM_DEBUG(dbgs() << "with this:\n");
- LLVM_DEBUG(ConstGEP->dump());
- GlobalToReplace->replaceAllUsesWith(ConstGEP);
- }
+ Constant *ConstGEP = ConstantExpr::getInBoundsGetElementPtr(
+ PooledStructType, GPool, Indices);
+ LLVM_DEBUG(dbgs() << "Replacing this global:\n");
+ LLVM_DEBUG(GlobalToReplace->dump());
+ LLVM_DEBUG(dbgs() << "with this:\n");
+ LLVM_DEBUG(ConstGEP->dump());
+ GlobalToReplace->replaceAllUsesWith(ConstGEP);
}
} // namespace
>From d53dbb9e0e7658d550f3014b1009c083cad9c5bd Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Wed, 22 May 2024 08:48:05 +0200
Subject: [PATCH 2/3] clang-format
---
llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp b/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
index b73e25d37f8f5..309938accdf4c 100644
--- a/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
+++ b/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
@@ -312,8 +312,8 @@ void PPCMergeStringPool::replaceUsesWithGEP(GlobalVariable *GlobalToReplace,
Indices.push_back(ConstantInt::get(Type::getInt32Ty(*Context), 0));
Indices.push_back(ConstantInt::get(Type::getInt32Ty(*Context), ElementIndex));
- Constant *ConstGEP = ConstantExpr::getInBoundsGetElementPtr(
- PooledStructType, GPool, Indices);
+ Constant *ConstGEP =
+ ConstantExpr::getInBoundsGetElementPtr(PooledStructType, GPool, Indices);
LLVM_DEBUG(dbgs() << "Replacing this global:\n");
LLVM_DEBUG(GlobalToReplace->dump());
LLVM_DEBUG(dbgs() << "with this:\n");
>From c6ab5a3a252961713349ba8992cfb8385b21c8ca Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Thu, 23 May 2024 09:04:56 +0200
Subject: [PATCH 3/3] Add test case
This previously produced use-after-free under asan.
---
.../PowerPC/mergeable-string-pool-pr92991.ll | 20 +++++++++++++++++++
1 file changed, 20 insertions(+)
create mode 100644 llvm/test/CodeGen/PowerPC/mergeable-string-pool-pr92991.ll
diff --git a/llvm/test/CodeGen/PowerPC/mergeable-string-pool-pr92991.ll b/llvm/test/CodeGen/PowerPC/mergeable-string-pool-pr92991.ll
new file mode 100644
index 0000000000000..4e9c69e5fe4cf
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/mergeable-string-pool-pr92991.ll
@@ -0,0 +1,20 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s
+
+ at g = private constant [4 x i32] [i32 122, i32 67, i32 35, i32 56]
+ at g2 = private constant [1 x i64] [i64 1], align 8
+
+define void @test(ptr %p, ptr %p2) {
+; CHECK-LABEL: test:
+; CHECK: # %bb.0:
+; CHECK-NEXT: addis 5, 2, .L__ModuleStringPool at toc@ha
+; CHECK-NEXT: addi 5, 5, .L__ModuleStringPool at toc@l
+; CHECK-NEXT: addi 6, 5, 12
+; CHECK-NEXT: std 6, 0(3)
+; CHECK-NEXT: addi 3, 5, 16
+; CHECK-NEXT: std 3, 0(4)
+; CHECK-NEXT: blr
+ store ptr getelementptr inbounds ([4 x i32], ptr @g, i64 0, i64 1), ptr %p
+ store ptr getelementptr inbounds ([4 x i32], ptr @g, i64 0, i64 2), ptr %p2
+ ret void
+}
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