[clang] [CodeGen][TBAA] Fix aliasing for char-derived pointer types (PR #200392)

[via cfe-commits]

https://github.com/PimpalkarNeha updated https://github.com/llvm/llvm-project/pull/200392

>From 933de211eb597e65bc83fffeb84216e328deb413 Mon Sep 17 00:00:00 2001
From: Neha Pimpalkar <Neha.Pimpalkar at amd.com>
Date: Fri, 29 May 2026 17:58:27 +0530
Subject: [PATCH] Fix pointer TBAA for char-derived pointer types

---
 clang/lib/CodeGen/CodeGenTBAA.cpp             |  3 +++
 .../test/CodeGen/tbaa-char-derived-pointers.c | 23 +++++++++++++++++++
 2 files changed, 26 insertions(+)
 create mode 100644 clang/test/CodeGen/tbaa-char-derived-pointers.c

diff --git a/clang/lib/CodeGen/CodeGenTBAA.cpp b/clang/lib/CodeGen/CodeGenTBAA.cpp
index 1854df7c7c0f1..fd596208c5d6e 100644
--- a/clang/lib/CodeGen/CodeGenTBAA.cpp
+++ b/clang/lib/CodeGen/CodeGenTBAA.cpp
@@ -286,6 +286,9 @@ llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
     SmallString<256> TyName;
     if (isa<BuiltinType>(Ty)) {
       llvm::MDNode *ScalarMD = getTypeInfoHelper(Ty);
+      // char-derived pointers alias everything; use the universal pointer node.
+      if (ScalarMD == getChar())
+        return getAnyPtr(PtrDepth);
       StringRef Name =
           cast<llvm::MDString>(
               ScalarMD->getOperand(CodeGenOpts.NewStructPathTBAA ? 2 : 0))
diff --git a/clang/test/CodeGen/tbaa-char-derived-pointers.c b/clang/test/CodeGen/tbaa-char-derived-pointers.c
new file mode 100644
index 0000000000000..6c18a8a74a1b2
--- /dev/null
+++ b/clang/test/CodeGen/tbaa-char-derived-pointers.c
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -O2 -disable-llvm-passes -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK,OLD
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -O2 -disable-llvm-passes -emit-llvm -new-struct-path-tbaa -o - %s | FileCheck %s --check-prefixes=CHECK,NEW
+//
+// char-derived pointers must use the generic "any pN pointer" TBAA node, not a
+// distinct "pN omnipotent char" sibling of "pN int" (which would imply NoAlias).
+
+void char_int_ptr_cast(int ***p) {
+  char ***c = (char ***)p;
+  *c = 0;
+  (void)*p;
+}
+
+// CHECK-LABEL: define dso_local void @char_int_ptr_cast(
+// CHECK: store ptr null, ptr {{.*}}, !tbaa !{{[0-9]+}}
+
+// OLD-DAG: !{{[0-9]+}} = !{!"p2 int", !{{[0-9]+}}, i64 0}
+// OLD-DAG: !{{[0-9]+}} = !{!"any p2 pointer", !{{[0-9]+}}, i64 0}
+
+// NEW-DAG: !{{[0-9]+}} = !{!{{[0-9]+}}, i64 8, !"p2 int"}
+// NEW-DAG: !{{[0-9]+}} = !{!{{[0-9]+}}, i64 8, !"any p2 pointer"}
+
+// CHECK-NOT: !{!"p2 omnipotent char"
+// CHECK-NOT: !{!"p3 omnipotent char"