[CodeGen][CFI] Generalize transparent union parameters #158193

vitalybuka · 2025-09-12T04:45:49Z

According GCC documentation transparent union
calling convention is the same as the type of the
first member of the union.

C++ ignores attribute.

Note, it does not generalize args of function pointer args.
It's unnecessary with pointer generalization.
It will be fixed in followup patch.

Created using spr 1.3.6

Created using spr 1.3.6 [skip ci]

llvmbot · 2025-09-12T04:46:19Z

@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang

Author: Vitaly Buka (vitalybuka)

Changes

According GCC documentation transparent union
calling convention is the same as the type of the
first member of the union.

C++ ignores attribute.

Full diff: https://github.com/llvm/llvm-project/pull/158193.diff

5 Files Affected:

(modified) clang/lib/CodeGen/CodeGenModule.cpp (+17-1)
(modified) clang/test/CodeGen/cfi-icall-generalize.c (+4-4)
(modified) clang/test/CodeGen/cfi-icall-normalize2.c (+2-2)
(modified) clang/test/CodeGen/kcfi-generalize.c (+4-4)
(modified) clang/test/CodeGen/kcfi-normalize.c (+6-4)

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index c647003ff389d..46dbd85665e5d 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2339,13 +2339,29 @@ llvm::ConstantInt *CodeGenModule::CreateCrossDsoCfiTypeId(llvm::Metadata *MD) {
   return llvm::ConstantInt::get(Int64Ty, llvm::MD5Hash(MDS->getString()));
 }
 
+static QualType GeneralizeTransparentUnion(QualType Ty) {
+  const RecordType *UT = Ty->getAsUnionType();
+  if (!UT)
+    return Ty;
+  const RecordDecl *UD = UT->getOriginalDecl()->getDefinitionOrSelf();
+  if (!UD->hasAttr<TransparentUnionAttr>())
+    return Ty;
+  for (const auto *it : UD->fields()) {
+    return it->getType();
+  }
+  return Ty;
+}
+
+static QualType GeneralizeTransparentUnion(QualType Ty) {
+}
+
 // Generalize pointer types to a void pointer with the qualifiers of the
 // originally pointed-to type, e.g. 'const char *' and 'char * const *'
 // generalize to 'const void *' while 'char *' and 'const char **' generalize to
 // 'void *'.
 static QualType GeneralizeType(ASTContext &Ctx, QualType Ty,
                                bool GeneralizePointers) {
-  // TODO: Add other generalizations.
+  Ty = GeneralizeTransparentUnion(Ty);
 
   if (!GeneralizePointers || !Ty->isPointerType())
     return Ty;
diff --git a/clang/test/CodeGen/cfi-icall-generalize.c b/clang/test/CodeGen/cfi-icall-generalize.c
index 116a99e4e2859..5359134805198 100644
--- a/clang/test/CodeGen/cfi-icall-generalize.c
+++ b/clang/test/CodeGen/cfi-icall-generalize.c
@@ -22,13 +22,13 @@ union Union {
 
 // CHECK: define{{.*}} void @uni({{.*}} !type [[TYPE2:![0-9]+]] !type [[TYPE2_GENERALIZED:![0-9]+]]
 void uni(void (*fn)(union Union), union Union arg1) {
-  // UNGENERALIZED: call i1 @llvm.type.test(ptr {{.*}}, metadata !"_ZTSFv5UnionE")
-  // GENERALIZED: call i1 @llvm.type.test(ptr {{.*}}, metadata !"_ZTSFv5UnionE.generalized")
+  // UNGENERALIZED: call i1 @llvm.type.test(ptr {{.*}}, metadata !"_ZTSFvPcE")
+  // GENERALIZED: call i1 @llvm.type.test(ptr {{.*}}, metadata !"_ZTSFvPvE.generalized")
     fn(arg1);
 }
 
 // CHECK: [[TYPE]] = !{i64 0, !"_ZTSFPPiPKcPS2_E"}
 // CHECK: [[TYPE_GENERALIZED]] = !{i64 0, !"_ZTSFPvPKvS_E.generalized"}
 
-// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFv5UnionES_E"}
-// CHECK: [[TYPE2_GENERALIZED]] = !{i64 0, !"_ZTSFvPv5UnionE.generalized"}
+// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFv5UnionEPcE"}
+// CHECK: [[TYPE2_GENERALIZED]] = !{i64 0, !"_ZTSFvPvS_E.generalized"}
diff --git a/clang/test/CodeGen/cfi-icall-normalize2.c b/clang/test/CodeGen/cfi-icall-normalize2.c
index c88ecc9f0c3f7..b9d9af7c8a47b 100644
--- a/clang/test/CodeGen/cfi-icall-normalize2.c
+++ b/clang/test/CodeGen/cfi-icall-normalize2.c
@@ -32,11 +32,11 @@ union Union {
 void uni(void (*fn)(union Union), union Union arg1) {
     // CHECK-LABEL: define{{.*}}uni
     // CHECK-SAME: {{.*}}!type ![[TYPE4:[0-9]+]] !type !{{[0-9]+}}
-    // CHECK: call i1 @llvm.type.test({{i8\*|ptr}} {{%f|%0}}, metadata !"_ZTSFv5UnionE.normalized")
+    // CHECK: call i1 @llvm.type.test({{i8\*|ptr}} {{%f|%0}}, metadata !"_ZTSFvPu2i8E.normalized")
     fn(arg1);
 }
 
 // CHECK: ![[TYPE1]] = !{i64 0, !"_ZTSFvPFvu3i32ES_E.normalized"}
 // CHECK: ![[TYPE2]] = !{i64 0, !"_ZTSFvPFvu3i32S_ES_S_E.normalized"}
 // CHECK: ![[TYPE3]] = !{i64 0, !"_ZTSFvPFvu3i32S_S_ES_S_S_E.normalized"}
-// CHECK: ![[TYPE4]] = !{i64 0, !"_ZTSFvPFv5UnionES_E.normalized"}
+// CHECK: ![[TYPE4]] = !{i64 0, !"_ZTSFvPFv5UnionEPu2i8E.normalized"}
diff --git a/clang/test/CodeGen/kcfi-generalize.c b/clang/test/CodeGen/kcfi-generalize.c
index 89b298f3e2faa..24e054549d527 100644
--- a/clang/test/CodeGen/kcfi-generalize.c
+++ b/clang/test/CodeGen/kcfi-generalize.c
@@ -33,8 +33,8 @@ union Union {
 
 // CHECK: define{{.*}} void @uni({{.*}} !kcfi_type [[TYPE2:![0-9]+]]
 void uni(void (*fn)(union Union), union Union arg1) {
-  // UNGENERALIZED: call {{.*}} [ "kcfi"(i32 -1037059548) ]
-  // GENERALIZED: call {{.*}} [ "kcfi"(i32 422130955) ]
+  // UNGENERALIZED: call {{.*}} [ "kcfi"(i32 -587217045) ]
+  // GENERALIZED: call {{.*}} [ "kcfi"(i32 2139530422) ]
     fn(arg1);
 }
 
@@ -44,5 +44,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
 // UNGENERALIZED: [[TYPE3]] = !{i32 874141567}
 // GENERALIZED: [[TYPE3]] = !{i32 954385378}
 
-// UNGENERALIZED: [[TYPE2]] = !{i32 981319178}
-// GENERALIZED: [[TYPE2]] = !{i32 -1599950473}
\ No newline at end of file
+// UNGENERALIZED: [[TYPE2]] = !{i32 -1619636625}
+// GENERALIZED: [[TYPE2]] = !{i32 -125078496}
\ No newline at end of file
diff --git a/clang/test/CodeGen/kcfi-normalize.c b/clang/test/CodeGen/kcfi-normalize.c
index cde784962d11a..08f5249b6d6c3 100644
--- a/clang/test/CodeGen/kcfi-normalize.c
+++ b/clang/test/CodeGen/kcfi-normalize.c
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers -o - %s | FileCheck %s
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers -x c++ -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers -o - %s | FileCheck %s --check-prefixes=CHECK,C
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers -x c++ -o - %s | FileCheck %s --check-prefixes=CHECK,CPP
 #if !__has_feature(kcfi)
 #error Missing kcfi?
 #endif
@@ -36,7 +36,8 @@ union Union {
 void uni(void (*fn)(union Union), union Union arg1) {
     // CHECK-LABEL: define{{.*}}uni
     // CHECK-SAME: {{.*}}!kcfi_type ![[TYPE4:[0-9]+]]
-    // CHECK: call void %0(ptr %1) [ "kcfi"(i32 -1430221633) ]
+    // C: call void %0(ptr %1) [ "kcfi"(i32 1819770848) ]
+    // CPP: call void %0(ptr %1) [ "kcfi"(i32 -1430221633) ]
     fn(arg1);
 }
 
@@ -44,4 +45,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
 // CHECK: ![[TYPE1]] = !{i32 -1143117868}
 // CHECK: ![[TYPE2]] = !{i32 -460921415}
 // CHECK: ![[TYPE3]] = !{i32 -333839615}
-// CHECK: ![[TYPE4]] = !{i32 1766237188}
\ No newline at end of file
+// C: ![[TYPE4]] = !{i32 -650530463}
+// CPP: ![[TYPE4]] = !{i32 1766237188}
\ No newline at end of file

github-actions · 2025-09-12T04:50:10Z

✅ With the latest revision this PR passed the C/C++ code formatter.

Created using spr 1.3.6

Created using spr 1.3.6 [skip ci]

Created using spr 1.3.6

Created using spr 1.3.6 [skip ci]

Created using spr 1.3.6

Created using spr 1.3.6 [skip ci]

Created using spr 1.3.6

Created using spr 1.3.6 [skip ci]

Created using spr 1.3.6

For #158193

…IdentifierGeneralized (#158190) For #158193

…ctionType (#158191) For #158193 --------- Co-authored-by: Alex Langford <[email protected]>

For #158193

Created using spr 1.3.6 [skip ci]

Created using spr 1.3.6

shafik · 2025-10-23T02:26:16Z

clang/lib/CodeGen/CodeGenModule.cpp

+  const RecordDecl *UD = UT->getOriginalDecl()->getDefinitionOrSelf();
+  if (!UD->hasAttr<TransparentUnionAttr>())
+    return Ty;
+  for (const auto *it : UD->fields()) {


Was it intentional to use a range based for loop here only to unconditionally return in the body?

The meaning is as intended, I think. Maybe something like if (!UD->fields().empty()) return UD->fields()[0]; would be better style.

Agreed, an if statement would signal intent better.

vitalybuka added 2 commits September 11, 2025 21:45

[𝘀𝗽𝗿] initial version

7170e27

Created using spr 1.3.6

[𝘀𝗽𝗿] changes to main this commit is based on

59e3ced

Created using spr 1.3.6 [skip ci]

llvmbot added clang Clang issues not falling into any other category clang:codegen IR generation bugs: mangling, exceptions, etc. labels Sep 12, 2025

vitalybuka mentioned this pull request Sep 12, 2025

[NFC][CodeGen][CFI] Extract CreateMetadataIdentifierForFnType #158189

Merged

vitalybuka requested review from fmayer, pcc and thurstond September 12, 2025 04:50

remove dead code

2eadc0d

Created using spr 1.3.6

thurstond approved these changes Sep 12, 2025

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vitalybuka mentioned this pull request Sep 12, 2025

[CodeGen][CFI] Generalize transparent union in args of args of functions #158194

Draft

vitalybuka added 8 commits September 11, 2025 22:02

[𝘀𝗽𝗿] changes introduced through rebase

9cdb7a3

Created using spr 1.3.6 [skip ci]

newline

5df6b7c

Created using spr 1.3.6

[𝘀𝗽𝗿] changes introduced through rebase

e96fc1f

Created using spr 1.3.6 [skip ci]

rebase

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Created using spr 1.3.6

[𝘀𝗽𝗿] changes introduced through rebase

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Created using spr 1.3.6 [skip ci]

spaces

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Created using spr 1.3.6

[𝘀𝗽𝗿] changes introduced through rebase

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TYPE4

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pcc approved these changes Sep 12, 2025

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vitalybuka added a commit that referenced this pull request Sep 12, 2025

[NFC][CodeGen][CFI] Extract CreateMetadataIdentifierForFnType (#158189)

bac9e46

For #158193

vitalybuka added a commit that referenced this pull request Sep 12, 2025

[NFC][CFI][CodeGen] Move GeneralizeFunctionType out of CreateMetadata…

8ac67aa

…IdentifierGeneralized (#158190) For #158193

vitalybuka added a commit that referenced this pull request Sep 13, 2025

[NFC][CodeGen][CFI] Add GeneralizePointers parameter to GeneralizeFun…

a5bff94

…ctionType (#158191) For #158193 --------- Co-authored-by: Alex Langford <[email protected]>

vitalybuka added a commit that referenced this pull request Sep 13, 2025

[NFC][CodeGen][CFI] Pre-commit transparent_union tests (#158192)

ba3b3e3

For #158193

[𝘀𝗽𝗿] changes introduced through rebase

2166ce8

Created using spr 1.3.6 [skip ci]

rebase

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Created using spr 1.3.6

vitalybuka changed the base branch from users/vitalybuka/spr/main.codegencfi-generalize-transparent-union-parameters to main September 13, 2025 01:51

vitalybuka enabled auto-merge (squash) September 13, 2025 01:51

vitalybuka merged commit 004f209 into main Sep 13, 2025
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vitalybuka deleted the users/vitalybuka/spr/codegencfi-generalize-transparent-union-parameters branch September 13, 2025 02:18

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