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

vitalybuka · 2025-09-12T04:45:53Z

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

C++ ignores attribute.

Follow up to #158193.

Created using spr 1.3.6

llvmbot · 2025-09-12T04:46:25Z

@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/158194.diff

5 Files Affected:

(modified) clang/lib/CodeGen/CodeGenModule.cpp (+12-5)
(modified) clang/test/CodeGen/cfi-icall-generalize.c (+1-1)
(modified) clang/test/CodeGen/cfi-icall-normalize2.c (+1-1)
(modified) clang/test/CodeGen/kcfi-generalize.c (+1-1)
(modified) clang/test/CodeGen/kcfi-normalize.c (+1-1)

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 46dbd85665e5d..44441df5ca6d8 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2352,8 +2352,8 @@ static QualType GeneralizeTransparentUnion(QualType Ty) {
   return Ty;
 }
 
-static QualType GeneralizeTransparentUnion(QualType Ty) {
-}
+static QualType GeneralizeFunctionType(ASTContext &Ctx, QualType Ty,
+                                       bool GeneralizePointers);
 
 // Generalize pointer types to a void pointer with the qualifiers of the
 // originally pointed-to type, e.g. 'const char *' and 'char * const *'
@@ -2363,12 +2363,19 @@ static QualType GeneralizeType(ASTContext &Ctx, QualType Ty,
                                bool GeneralizePointers) {
   Ty = GeneralizeTransparentUnion(Ty);
 
-  if (!GeneralizePointers || !Ty->isPointerType())
+  if (!Ty->isPointerType())
+    return Ty;
+
+  QualType PTy = Ty->getPointeeType();
+  if (PTy->getAs<FunctionProtoType>() || PTy->getAs<FunctionNoProtoType>())
+    Ty = Ctx.getPointerType(
+        GeneralizeFunctionType(Ctx, PTy, GeneralizePointers));
+
+  if (!GeneralizePointers)
     return Ty;
 
   return Ctx.getPointerType(
-      QualType(Ctx.VoidTy)
-          .withCVRQualifiers(Ty->getPointeeType().getCVRQualifiers()));
+      QualType(Ctx.VoidTy).withCVRQualifiers(PTy.getCVRQualifiers()));
 }
 
 // Apply type generalization to a FunctionType's return and argument types
diff --git a/clang/test/CodeGen/cfi-icall-generalize.c b/clang/test/CodeGen/cfi-icall-generalize.c
index 5359134805198..6659d76fbbbb2 100644
--- a/clang/test/CodeGen/cfi-icall-generalize.c
+++ b/clang/test/CodeGen/cfi-icall-generalize.c
@@ -30,5 +30,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
 // CHECK: [[TYPE]] = !{i64 0, !"_ZTSFPPiPKcPS2_E"}
 // CHECK: [[TYPE_GENERALIZED]] = !{i64 0, !"_ZTSFPvPKvS_E.generalized"}
 
-// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFv5UnionEPcE"}
+// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFvPcES_E"}
 // 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 b9d9af7c8a47b..49b279c04fd56 100644
--- a/clang/test/CodeGen/cfi-icall-normalize2.c
+++ b/clang/test/CodeGen/cfi-icall-normalize2.c
@@ -39,4 +39,4 @@ void uni(void (*fn)(union Union), union Union 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, !"_ZTSFvPFv5UnionEPu2i8E.normalized"}
+// CHECK: ![[TYPE4]] = !{i64 0, !"_ZTSFvPFvPu2i8ES0_E.normalized"}
diff --git a/clang/test/CodeGen/kcfi-generalize.c b/clang/test/CodeGen/kcfi-generalize.c
index 24e054549d527..91f2be7b74818 100644
--- a/clang/test/CodeGen/kcfi-generalize.c
+++ b/clang/test/CodeGen/kcfi-generalize.c
@@ -44,5 +44,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
 // UNGENERALIZED: [[TYPE3]] = !{i32 874141567}
 // GENERALIZED: [[TYPE3]] = !{i32 954385378}
 
-// UNGENERALIZED: [[TYPE2]] = !{i32 -1619636625}
+// UNGENERALIZED: [[TYPE2]] = !{i32 -1954865805}
 // 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 08f5249b6d6c3..532959a7d30fd 100644
--- a/clang/test/CodeGen/kcfi-normalize.c
+++ b/clang/test/CodeGen/kcfi-normalize.c
@@ -45,5 +45,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
 // CHECK: ![[TYPE1]] = !{i32 -1143117868}
 // CHECK: ![[TYPE2]] = !{i32 -460921415}
 // CHECK: ![[TYPE3]] = !{i32 -333839615}
-// C: ![[TYPE4]] = !{i32 -650530463}
+// C: ![[TYPE4]] = !{i32 1186327125}
 // CPP: ![[TYPE4]] = !{i32 1766237188}
\ No newline at end of file

llvmbot · 2025-09-12T04:46:25Z

@llvm/pr-subscribers-clang-codegen

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/158194.diff

5 Files Affected:

(modified) clang/lib/CodeGen/CodeGenModule.cpp (+12-5)
(modified) clang/test/CodeGen/cfi-icall-generalize.c (+1-1)
(modified) clang/test/CodeGen/cfi-icall-normalize2.c (+1-1)
(modified) clang/test/CodeGen/kcfi-generalize.c (+1-1)
(modified) clang/test/CodeGen/kcfi-normalize.c (+1-1)

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 46dbd85665e5d..44441df5ca6d8 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2352,8 +2352,8 @@ static QualType GeneralizeTransparentUnion(QualType Ty) {
   return Ty;
 }
 
-static QualType GeneralizeTransparentUnion(QualType Ty) {
-}
+static QualType GeneralizeFunctionType(ASTContext &Ctx, QualType Ty,
+                                       bool GeneralizePointers);
 
 // Generalize pointer types to a void pointer with the qualifiers of the
 // originally pointed-to type, e.g. 'const char *' and 'char * const *'
@@ -2363,12 +2363,19 @@ static QualType GeneralizeType(ASTContext &Ctx, QualType Ty,
                                bool GeneralizePointers) {
   Ty = GeneralizeTransparentUnion(Ty);
 
-  if (!GeneralizePointers || !Ty->isPointerType())
+  if (!Ty->isPointerType())
+    return Ty;
+
+  QualType PTy = Ty->getPointeeType();
+  if (PTy->getAs<FunctionProtoType>() || PTy->getAs<FunctionNoProtoType>())
+    Ty = Ctx.getPointerType(
+        GeneralizeFunctionType(Ctx, PTy, GeneralizePointers));
+
+  if (!GeneralizePointers)
     return Ty;
 
   return Ctx.getPointerType(
-      QualType(Ctx.VoidTy)
-          .withCVRQualifiers(Ty->getPointeeType().getCVRQualifiers()));
+      QualType(Ctx.VoidTy).withCVRQualifiers(PTy.getCVRQualifiers()));
 }
 
 // Apply type generalization to a FunctionType's return and argument types
diff --git a/clang/test/CodeGen/cfi-icall-generalize.c b/clang/test/CodeGen/cfi-icall-generalize.c
index 5359134805198..6659d76fbbbb2 100644
--- a/clang/test/CodeGen/cfi-icall-generalize.c
+++ b/clang/test/CodeGen/cfi-icall-generalize.c
@@ -30,5 +30,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
 // CHECK: [[TYPE]] = !{i64 0, !"_ZTSFPPiPKcPS2_E"}
 // CHECK: [[TYPE_GENERALIZED]] = !{i64 0, !"_ZTSFPvPKvS_E.generalized"}
 
-// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFv5UnionEPcE"}
+// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFvPcES_E"}
 // 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 b9d9af7c8a47b..49b279c04fd56 100644
--- a/clang/test/CodeGen/cfi-icall-normalize2.c
+++ b/clang/test/CodeGen/cfi-icall-normalize2.c
@@ -39,4 +39,4 @@ void uni(void (*fn)(union Union), union Union 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, !"_ZTSFvPFv5UnionEPu2i8E.normalized"}
+// CHECK: ![[TYPE4]] = !{i64 0, !"_ZTSFvPFvPu2i8ES0_E.normalized"}
diff --git a/clang/test/CodeGen/kcfi-generalize.c b/clang/test/CodeGen/kcfi-generalize.c
index 24e054549d527..91f2be7b74818 100644
--- a/clang/test/CodeGen/kcfi-generalize.c
+++ b/clang/test/CodeGen/kcfi-generalize.c
@@ -44,5 +44,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
 // UNGENERALIZED: [[TYPE3]] = !{i32 874141567}
 // GENERALIZED: [[TYPE3]] = !{i32 954385378}
 
-// UNGENERALIZED: [[TYPE2]] = !{i32 -1619636625}
+// UNGENERALIZED: [[TYPE2]] = !{i32 -1954865805}
 // 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 08f5249b6d6c3..532959a7d30fd 100644
--- a/clang/test/CodeGen/kcfi-normalize.c
+++ b/clang/test/CodeGen/kcfi-normalize.c
@@ -45,5 +45,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
 // CHECK: ![[TYPE1]] = !{i32 -1143117868}
 // CHECK: ![[TYPE2]] = !{i32 -460921415}
 // CHECK: ![[TYPE3]] = !{i32 -333839615}
-// C: ![[TYPE4]] = !{i32 -650530463}
+// C: ![[TYPE4]] = !{i32 1186327125}
 // CPP: ![[TYPE4]] = !{i32 1766237188}
\ No newline at end of file

Created using spr 1.3.6

pcc · 2025-09-12T18:24:48Z

clang/lib/CodeGen/CodeGenModule.cpp

+    return Ty;
+
+  QualType PTy = Ty->getPointeeType();
+  if (PTy->getAs<FunctionProtoType>() || PTy->getAs<FunctionNoProtoType>())


I guess this is not the only way you can end up with a function type. E.g. pointer to pointer to function, reference to pointer to function, etc.

What do you think about doing this in the mangler? E.g. add a call to a hook near the top of void CXXNameMangler::mangleType(QualType T) and supply a hook that does the transparent_union generalization from here.

Mangler is too late, if we have pointer generalization, it should apply to pointers form transparent union

The hook could also do the pointer generalization, no?

[𝘀𝗽𝗿] initial version

ca337d0

Created using spr 1.3.6

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

rebase

580126f

Created using spr 1.3.6

vitalybuka requested review from fmayer, pcc and thurstond September 12, 2025 05:00

vitalybuka added 4 commits September 11, 2025 22:02

newline

941dd06

Created using spr 1.3.6

rebase

b9e6b83

Created using spr 1.3.6

spaces

aab4258

Created using spr 1.3.6

TYPE4

dfb7c98

Created using spr 1.3.6

pcc reviewed Sep 12, 2025

View reviewed changes

vitalybuka requested a review from pcc September 12, 2025 20:52

vitalybuka marked this pull request as draft September 16, 2025 20:52

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

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

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

Uh oh!

vitalybuka commented Sep 12, 2025 •

edited

Loading

Uh oh!

llvmbot commented Sep 12, 2025

Uh oh!

llvmbot commented Sep 12, 2025

Uh oh!

pcc Sep 12, 2025

Uh oh!

vitalybuka Sep 12, 2025

Uh oh!

pcc Sep 12, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

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

Are you sure you want to change the base?

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

Uh oh!

Conversation

vitalybuka commented Sep 12, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

llvmbot commented Sep 12, 2025

Uh oh!

llvmbot commented Sep 12, 2025

Uh oh!

pcc Sep 12, 2025

Choose a reason for hiding this comment

Uh oh!

vitalybuka Sep 12, 2025

Choose a reason for hiding this comment

Uh oh!

pcc Sep 12, 2025

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

vitalybuka commented Sep 12, 2025 •

edited

Loading