| Issue |
184747
|
| Summary |
[Clang] Assignment to a member array of a comma operator result
|
| Labels |
clang,
clang:codegen
|
| Assignees |
|
| Reporter |
s-watanabe314
|
In the test program below, the return value of the comma operator is the `obj2` struct, and an assignment is made to its member array. However, when the value is referenced later, the value has not been assigned. This behavior started after patch #133472.
- test.c (Original program: [0044_0007.c](https://github.com/fujitsu/compiler-test-suite/blob/main/C/0044/0044_0007.c))
```C
#include <stdio.h>
struct test02 {
int array[10];
};
int main()
{
struct test02 obj2 = { 0 };
(0,obj2).array[3] = 5;
printf("%d\n", obj2.array[3]);
return 0;
}
```
- Result
```
$ clang -v
clang version 23.0.0git (https://github.com/llvm/llvm-project.git 7b26069828aa88064b92f73f764b708754e441ec)
$ clang test.c -O0 -o test.out
$ ./test.out
0
```
In the LLVM IR, the `store` and `load` operations were performed on different pointers.
- test.ll ([godbolt](https://godbolt.org/z/5q6hjEMc6))
```
define dso_local i32 @main() #0 {
%1 = alloca i32, align 4
%2 = alloca %struct.test02, align 4
%3 = alloca %struct.test02, align 4
store i32 0, ptr %1, align 4
call void @llvm.memset.p0.i64(ptr align 4 %2, i8 0, i64 40, i1 false)
call void @llvm.memcpy.p0.p0.i64(ptr align 4 %3, ptr align 4 %2, i64 40, i1 false)
%4 = getelementptr inbounds nuw %struct.test02, ptr %3, i32 0, i32 0
%5 = getelementptr inbounds [10 x i32], ptr %4, i64 0, i64 3
store i32 5, ptr %5, align 4
%6 = getelementptr inbounds nuw %struct.test02, ptr %2, i32 0, i32 0
%7 = getelementptr inbounds [10 x i32], ptr %6, i64 0, i64 3
%8 = load i32, ptr %7, align 4
%9 = call i32 (ptr, ...) @printf(ptr noundef @.str, i32 noundef %8)
ret i32 0
}
```
Is this the expected behavior based on the C language standard? Should Clang issue a compile-time error or warning?
![]()
_______________________________________________
llvm-bugs mailing list
[email protected]
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
