| Issue |
60974
|
| Summary |
[Clang15] clang -O stops emitting code for function when indeterminate value encountered in controlling condition of `if`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
ian-abbott
|
Consider this invalid program using an uninitialized variable:
**foo.c**
```c
#include <stdio.h>
int main (void)
{
int garbage; // garbage is indeterminate
int *addr = &garbage; // address of garbage has been used
int a = 0;
puts("Garbage test");
fflush(stdout);
if (garbage)
{
a = 1;
}
printf("a = %d\n", a);
fflush(stdout);
}
```
Compiling to assembly language with clang-15 on Debian, with optimizer enabled:
```text
$ clang-15 -O -S foo.c
```
Details of compiler used:
```text
$ clang-15 --version
Debian clang version 15.0.6
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
```
Resulting assembly language:
**foo.s**
```gas
.text
.file "foo.c"
.globl main # -- Begin function main
.p2align 4, 0x90
.type main,@function
main: # @main
.cfi_startproc
# %bb.0:
pushq %rax
.cfi_def_cfa_offset 16
leaq .L.str(%rip), %rdi
callq puts@PLT
movq stdout@GOTPCREL(%rip), %rax
movq (%rax), %rdi
callq fflush@PLT
.Lfunc_end0:
.size main, .Lfunc_end0-main
.cfi_endproc
# -- End function
.type .L.str,@object # @.str
.section .rodata.str1.1,"aMS",@progbits,1
.L.str:
.asciz "Garbage test"
.size .L.str, 13
.ident "Debian clang version 15.0.6"
.section ".note.GNU-stack","",@progbits
.addrsig
```
Note that no assembly code been emitted for the C code from the line `if (garbage)` to the end of the function, including any code to return from the function.
Related question by user **Lundin** (not me) on Stackoverflow:
https://stackoverflow.com/q/75533693/5264491
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