https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104237
Bug ID: 104237
Summary: Emitted binary code changes when -g is enabled at -O1
-flto
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: tlwang at uwaterloo dot ca
CC: marxin at gcc dot gnu.org
Target Milestone: ---
This occurs when compiling attributes_transformed_program0_preprocessed.c, as
shown below.
$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/scratch/software/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/12.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /tmp/tmp.scGtRTj8uf-gcc-builder/gcc/configure
--enable-languages=c,c++,lto --enable-checking-yes --enable-multiarch
--prefix=/scratch/software/gcc-trunk --disable-bootstrap
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.1 20220125 (experimental) [master -gf4ee27d32] (GCC)
$ cat attributes_transformed_program0_preprocessed.c
# 6 ""
short a;
__attribute__((optimize(0))) int b();
__attribute__((always_inline)) signed char c();
int b() {
char e = c();
return a;
}
signed char c(f) {
d();
# 7 "attributes_transformed_program0.c"
int g;
# 6
return f;
}
void d() {}
int main() {}
$ gcc-trunk -w -O1 -flto attributes_transformed_program0_preprocessed.c -o
a.out
$ objdump --disassemble --section=.text a.out > no_debug.txt
$ gcc-trunk -w -O1 -flto -g attributes_transformed_program0_preprocessed.c -o
a.out
$ objdump --disassemble --section=.text a.out > debug.txt
$ diff debug.txt no_debug.txt
18c18
< 401041: 48 c7 c7 1e 11 40 00 mov $0x40111e,%rdi
---
> 401041: 48 c7 c7 1d 11 40 00 mov $0x40111d,%rdi
88,91c88,91
< 40110d: 90 nop
< 40110e: 88 45 ff mov %al,-0x1(%rbp)
< 401111: 0f b7 05 ec 0e 00 00 movzwl 0xeec(%rip),%eax # 402004
<a>
< 401118: 98 cwtl
---
> 40110d: 88 45 ff mov %al,-0x1(%rbp)
> 401110: 0f b7 05 ed 0e 00 00 movzwl 0xeed(%rip),%eax # 402004
> <a>
> 401117: 98 cwtl
> 401118: 90 nop
93,95c93,94
< 40111a: 90 nop
< 40111b: 5d pop %rbp
< 40111c: c3 retq
---
> 40111a: 5d pop %rbp
> 40111b: c3 retq
97,98c96,97
< 000000000040111d <d>:
< 40111d: c3 retq
---
> 000000000040111c <d>:
> 40111c: c3 retq
100,105c99,104
< 000000000040111e <main>:
< 40111e: b8 00 00 00 00 mov $0x0,%eax
< 401123: c3 retq
< 401124: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
< 40112b: 00 00 00
< 40112e: 66 90 xchg %ax,%ax
---
> 000000000040111d <main>:
> 40111d: b8 00 00 00 00 mov $0x0,%eax
> 401122: c3 retq
> 401123: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
> 40112a: 00 00 00
> 40112d: 0f 1f 00 nopl (%rax)
