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[clang] Automatically add the returns_twice attribute to certain functions even if -fno-builtin is set #133511

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Merged
alanzhao1 merged 1 commit into from
Mar 31, 2025
Merged

[clang] Automatically add the returns_twice attribute to certain functions even if -fno-builtin is set #133511

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9 changes: 9 additions & 0 deletions clang/lib/CodeGen/CGCall.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2607,6 +2607,15 @@ void CodeGenModule::ConstructAttributeList(StringRef Name,
if (shouldDisableTailCalls())
FuncAttrs.addAttribute("disable-tail-calls", "true");

// These functions require the returns_twice attribute for correct codegen,
// but the attribute may not be added if -fno-builtin is specified. We
// explicitly add that attribute here.
static const llvm::StringSet<> ReturnsTwiceFn{
"_setjmpex", "setjmp", "_setjmp", "vfork",
"sigsetjmp", "__sigsetjmp", "savectx", "getcontext"};
if (ReturnsTwiceFn.contains(Name))
FuncAttrs.addAttribute(llvm::Attribute::ReturnsTwice);

// CPU/feature overrides. addDefaultFunctionDefinitionAttributes
// handles these separately to set them based on the global defaults.
GetCPUAndFeaturesAttributes(CalleeInfo.getCalleeDecl(), FuncAttrs);
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5 changes: 4 additions & 1 deletion clang/test/CodeGen/2003-08-20-vfork-bug.c
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@@ -1,5 +1,8 @@
// RUN: %clang_cc1 -emit-llvm %s -o /dev/null
// RUN: %clang_cc1 -x c %s -triple x86_64-linux-gnu -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 -x c %s -triple x86_64-linux-gnu -emit-llvm -fno-builtin -o - | FileCheck %s

// CHECK: ; Function Attrs: returns_twice
// CHECK-NEXT: declare {{.*}} @vfork(
extern int vfork(void);
void test() {
vfork();
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15 changes: 15 additions & 0 deletions clang/test/CodeGen/setjmp.c
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@@ -1,25 +1,31 @@
// RUN: %clang_cc1 -x c %s -triple x86_64-linux-gnu -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 -x c %s -triple x86_64-linux-gnu -emit-llvm -fno-builtin -o - | FileCheck %s
// RUN: %clang_cc1 -x c++ %s -triple x86_64-linux-gnu -emit-llvm -o - | FileCheck %s

#ifdef __cplusplus
extern "C" {
#endif

struct __jmp_buf_tag { int n; };
struct __ucontext_t_tag { int n; };
int setjmp(struct __jmp_buf_tag*);
int sigsetjmp(struct __jmp_buf_tag*, int);
int _setjmp(struct __jmp_buf_tag*);
int __sigsetjmp(struct __jmp_buf_tag*, int);
int _setjmpex(struct __jmp_buf_tag* env);
int getcontext(struct __ucontext_t_tag*);

typedef struct __jmp_buf_tag jmp_buf[1];
typedef struct __jmp_buf_tag sigjmp_buf[1];
typedef struct __ucontext_t_tag ucontext_t[1];

#ifdef __cplusplus
}
#endif

void f(void) {
jmp_buf jb;
ucontext_t ut;
// CHECK: call {{.*}}@setjmp(
setjmp(jb);
// CHECK: call {{.*}}@sigsetjmp(
Expand All @@ -28,6 +34,10 @@ void f(void) {
_setjmp(jb);
// CHECK: call {{.*}}@__sigsetjmp(
__sigsetjmp(jb, 0);
// CHECK: call {{.*}}@_setjmpex(
_setjmpex(jb);
// CHECK: call {{.*}}@getcontext(
getcontext(ut);
}

// CHECK: ; Function Attrs: returns_twice
Expand All @@ -42,3 +52,8 @@ void f(void) {
// CHECK: ; Function Attrs: returns_twice
// CHECK-NEXT: declare {{.*}} @__sigsetjmp(

// CHECK: ; Function Attrs: returns_twice
// CHECK-NEXT: declare {{.*}} @_setjmpex(

// CHECK: ; Function Attrs: returns_twice
// CHECK-NEXT: declare {{.*}} @getcontext(