[clang] [Clang][CodeGen] Do not set inbounds flag in `EmitMemberDataPointerAddress` when the base pointer is null (PR #130952)

[Yingwei Zheng via cfe-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/130952

See also https://github.com/llvm/llvm-project/pull/130734 for the original motivation.

This pattern (`container_of`) is also widely used by real-world programs.
Examples:
https://github.com/llvm/llvm-project/blob/1d89d7d5d76e391b035f50343e2a4890506c6f2b/llvm/include/llvm/IR/SymbolTableListTraits.h#L77-L87
https://github.com/nodejs/node/blob/a2a53cb728ec5f776ac16879ce0f480a8e838320/src/util-inl.h#L134-L137
https://github.com/search?q=*%29nullptr-%3E*&type=code


>From 824a5e7551437233ed6a7990d43572b8c50a5397 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 12 Mar 2025 20:17:28 +0800
Subject: [PATCH] [Clang][CodeGen] Do not set inbounds in
 `EmitMemberDataPointerAddress` when the base pointer is null

---
 clang/lib/CodeGen/ItaniumCXXABI.cpp           | 11 +++++++---
 clang/lib/CodeGen/MicrosoftCXXABI.cpp         | 10 ++++++---
 .../microsoft-abi-member-pointers.cpp         | 21 +++++++++++++++++++
 .../CodeGenCXX/pointers-to-data-members.cpp   | 21 +++++++++++++++++++
 4 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index b145da0f0ec09..b2eaea683ebe7 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -872,9 +872,14 @@ llvm::Value *ItaniumCXXABI::EmitMemberDataPointerAddress(
 
   CGBuilderTy &Builder = CGF.Builder;
 
-  // Apply the offset, which we assume is non-null.
-  return Builder.CreateInBoundsGEP(CGF.Int8Ty, Base.emitRawPointer(CGF), MemPtr,
-                                   "memptr.offset");
+  // Apply the offset.
+  // Specially, we don't add inbounds flags if the base pointer is a constant
+  // null. This is a workaround for old-style container_of macros.
+  llvm::Value *BaseAddr = Base.emitRawPointer(CGF);
+  return Builder.CreateGEP(CGF.Int8Ty, BaseAddr, MemPtr, "memptr.offset",
+                           isa<llvm::ConstantPointerNull>(BaseAddr)
+                               ? llvm::GEPNoWrapFlags::none()
+                               : llvm::GEPNoWrapFlags::inBounds());
 }
 
 // See if it's possible to return a constant signed pointer.
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 4b55fc3f17bd7..3501b2b2fdca8 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -3265,9 +3265,13 @@ llvm::Value *MicrosoftCXXABI::EmitMemberDataPointerAddress(
     Addr = Base.emitRawPointer(CGF);
   }
 
-  // Apply the offset, which we assume is non-null.
-  return Builder.CreateInBoundsGEP(CGF.Int8Ty, Addr, FieldOffset,
-                                   "memptr.offset");
+  // Apply the offset.
+  // Specially, we don't add inbounds flags if the base pointer is a constant
+  // null. This is a workaround for old-style container_of macros.
+  return Builder.CreateGEP(CGF.Int8Ty, Addr, FieldOffset, "memptr.offset",
+                           isa<llvm::ConstantPointerNull>(Addr)
+                               ? llvm::GEPNoWrapFlags::none()
+                               : llvm::GEPNoWrapFlags::inBounds());
 }
 
 llvm::Value *
diff --git a/clang/test/CodeGenCXX/microsoft-abi-member-pointers.cpp b/clang/test/CodeGenCXX/microsoft-abi-member-pointers.cpp
index fc8a31e0350e5..fe4cab164249f 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-member-pointers.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-member-pointers.cpp
@@ -964,3 +964,24 @@ static_assert(sizeof(b::d) == 16, "");
 static_assert(sizeof(void (a<int>::*)()) == 16, "");
 #endif
 }
+
+namespace ContainerOf {
+  using size_t = unsigned long long;
+
+  struct List {
+    int data;
+  };
+
+  struct Node {
+    int data;
+    struct List list1;
+    struct List list2;
+  };
+
+  // CHECK-LABEL: define{{.*}} ptr @"?getOwner at ContainerOf@@
+  // CHECK: %memptr.offset = getelementptr i8, ptr null, {{.*}}
+  Node* getOwner(List *list, List Node::*member) {
+    size_t offset = reinterpret_cast<size_t>(&((Node*)nullptr->*member));
+    return reinterpret_cast<Node*>(reinterpret_cast<char*>(list) - offset);
+  }
+}
diff --git a/clang/test/CodeGenCXX/pointers-to-data-members.cpp b/clang/test/CodeGenCXX/pointers-to-data-members.cpp
index cf1d6c018409d..2ee6c65cf167d 100644
--- a/clang/test/CodeGenCXX/pointers-to-data-members.cpp
+++ b/clang/test/CodeGenCXX/pointers-to-data-members.cpp
@@ -265,3 +265,24 @@ namespace PR47864 {
   struct D : B { int m; };
   auto x = (int B::*)&D::m;
 }
+
+namespace ContainerOf {
+  using size_t = unsigned long long;
+
+  struct List {
+    int data;
+  };
+
+  struct Node {
+    int data;
+    struct List list1;
+    struct List list2;
+  };
+
+  // CHECK-LABEL: define{{.*}} ptr @_ZN11ContainerOf8getOwnerEPNS_4ListEMNS_4NodeES0_
+  // CHECK: %memptr.offset = getelementptr i8, ptr null, i64 {{.*}}
+  Node* getOwner(List *list, List Node::*member) {
+    size_t offset = reinterpret_cast<size_t>(&((Node*)nullptr->*member));
+    return reinterpret_cast<Node*>(reinterpret_cast<char*>(list) - offset);
+  }
+}