[llvm] [MergeFunctions] Fix merging functions with different KCFI type identifiers (PR #217665)

[via llvm-commits]

https://github.com/Lane0218 updated https://github.com/llvm/llvm-project/pull/217665

>From 6996e634dee1a7b05f83c9fd949aea37c695a0a2 Mon Sep 17 00:00:00 2001
From: Lane0218 <laneljc at qq.com>
Date: Thu, 20 Aug 2026 23:26:33 +0800
Subject: [PATCH 1/2] [MergeFunctions] Fix merging functions with different
 KCFI type identifiers

---
 llvm/docs/MergeFunctions.md                   |  2 ++
 .../Transforms/Utils/FunctionComparator.cpp   |  4 +++
 .../MergeFunc/kcfi-function-merging.ll        | 36 +++++++++++++++++++
 3 files changed, 42 insertions(+)
 create mode 100644 llvm/test/Transforms/MergeFunc/kcfi-function-merging.ll

diff --git a/llvm/docs/MergeFunctions.md b/llvm/docs/MergeFunctions.md
index bb39e40032894..adc8bcec7c5d4 100644
--- a/llvm/docs/MergeFunctions.md
+++ b/llvm/docs/MergeFunctions.md
@@ -279,6 +279,8 @@ properties to be compared on this stage:
    - *Variable arguments*. *LHS* and *RHS* should be both either with or
      without *var-args*.
    - *Calling convention* should be the same.
+   - *KCFI type metadata*. Function-level `!kcfi_type` metadata, if present,
+     should be identical.
 
 2. Function type. Checked by `FunctionComparator::cmpType(Type*, Type*)`
 method. It checks return type and parameters type; the method itself will be
diff --git a/llvm/lib/Transforms/Utils/FunctionComparator.cpp b/llvm/lib/Transforms/Utils/FunctionComparator.cpp
index 05c24af6efb39..9e84c78087303 100644
--- a/llvm/lib/Transforms/Utils/FunctionComparator.cpp
+++ b/llvm/lib/Transforms/Utils/FunctionComparator.cpp
@@ -990,6 +990,10 @@ int FunctionComparator::compareSignature() const {
   if (int Res = cmpAttrs(FnL->getAttributes(), FnR->getAttributes()))
     return Res;
 
+  if (int Res = cmpMDNode(FnL->getMetadata(LLVMContext::MD_kcfi_type),
+                          FnR->getMetadata(LLVMContext::MD_kcfi_type)))
+    return Res;
+
   if (int Res = cmpNumbers(FnL->hasGC(), FnR->hasGC()))
     return Res;
 
diff --git a/llvm/test/Transforms/MergeFunc/kcfi-function-merging.ll b/llvm/test/Transforms/MergeFunc/kcfi-function-merging.ll
new file mode 100644
index 0000000000000..c3d3daadc5f51
--- /dev/null
+++ b/llvm/test/Transforms/MergeFunc/kcfi-function-merging.ll
@@ -0,0 +1,36 @@
+; RUN: opt -S -passes=mergefunc < %s | FileCheck %s
+
+; Functions with different KCFI type identifiers must not be merged.
+
+define internal i32 @a() unnamed_addr !kcfi_type !0 {
+; CHECK-LABEL: define internal i32 @a()
+; CHECK-NEXT: entry:
+; CHECK-NEXT: ret i32 0
+; CHECK-NEXT: }
+entry:
+  ret i32 0
+}
+
+define internal i32 @b() unnamed_addr !kcfi_type !1 {
+; CHECK-LABEL: define internal i32 @b()
+; CHECK-NEXT: entry:
+; CHECK-NEXT: ret i32 0
+; CHECK-NEXT: }
+entry:
+  ret i32 0
+}
+
+define i32 @caller() {
+; CHECK-LABEL: define i32 @caller()
+; CHECK-NEXT: entry:
+; CHECK-NEXT: %x = call i32 @a()
+; CHECK-NEXT: %y = call i32 @b()
+; CHECK-NEXT: ret i32 %y
+entry:
+  %x = call i32 @a()
+  %y = call i32 @b()
+  ret i32 %y
+}
+
+!0 = !{i32 1234}
+!1 = !{i32 6789}

>From 1d681d4dd119d08ed7b65a11d4183d97ada1e165 Mon Sep 17 00:00:00 2001
From: Lane0218 <laneljc at qq.com>
Date: Fri, 21 Aug 2026 13:56:42 +0800
Subject: [PATCH 2/2] [MergeFunctions] Update KCFI test checks

---
 .../MergeFunc/kcfi-function-merging.ll        | 34 ++++++++++++-------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/llvm/test/Transforms/MergeFunc/kcfi-function-merging.ll b/llvm/test/Transforms/MergeFunc/kcfi-function-merging.ll
index c3d3daadc5f51..90843e3bf6e84 100644
--- a/llvm/test/Transforms/MergeFunc/kcfi-function-merging.ll
+++ b/llvm/test/Transforms/MergeFunc/kcfi-function-merging.ll
@@ -1,31 +1,35 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
 ; RUN: opt -S -passes=mergefunc < %s | FileCheck %s
 
 ; Functions with different KCFI type identifiers must not be merged.
 
 define internal i32 @a() unnamed_addr !kcfi_type !0 {
-; CHECK-LABEL: define internal i32 @a()
-; CHECK-NEXT: entry:
-; CHECK-NEXT: ret i32 0
-; CHECK-NEXT: }
+; CHECK-LABEL: define internal i32 @a(
+; CHECK-SAME: ) unnamed_addr !kcfi_type [[META0:![0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    ret i32 0
+;
 entry:
   ret i32 0
 }
 
 define internal i32 @b() unnamed_addr !kcfi_type !1 {
-; CHECK-LABEL: define internal i32 @b()
-; CHECK-NEXT: entry:
-; CHECK-NEXT: ret i32 0
-; CHECK-NEXT: }
+; CHECK-LABEL: define internal i32 @b(
+; CHECK-SAME: ) unnamed_addr !kcfi_type [[META1:![0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    ret i32 0
+;
 entry:
   ret i32 0
 }
 
 define i32 @caller() {
-; CHECK-LABEL: define i32 @caller()
-; CHECK-NEXT: entry:
-; CHECK-NEXT: %x = call i32 @a()
-; CHECK-NEXT: %y = call i32 @b()
-; CHECK-NEXT: ret i32 %y
+; CHECK-LABEL: define i32 @caller() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[X:%.*]] = call i32 @a()
+; CHECK-NEXT:    [[Y:%.*]] = call i32 @b()
+; CHECK-NEXT:    ret i32 [[Y]]
+;
 entry:
   %x = call i32 @a()
   %y = call i32 @b()
@@ -34,3 +38,7 @@ entry:
 
 !0 = !{i32 1234}
 !1 = !{i32 6789}
+;.
+; CHECK: [[META0]] = !{i32 1234}
+; CHECK: [[META1]] = !{i32 6789}
+;.