https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102540
Bug ID: 102540
Summary: Dead Code Elimination Regression at -O3 (trunk vs
11.2.0)
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: theodoridisgr at gmail dot com
Target Milestone: ---
cat test.c
static long a;
static unsigned b;
void foo(void);
int main() {
long c, e;
c = b = a;
e = c ? 2 / (c + 1) : 0;
if (e && !b)
foo();
a = 0;
}
11.2.0 at -O3 can eliminate the call to foo but trunk at -O3 cannot:
gcc-11 -v
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (GCC)
gcc-11 test.c -S -O3
cat test.s
.file "test.c"
.text
.section .text.startup,"ax",@progbits
.p2align 4
.globl main
.type main, @function
main:
.LFB0:
.cfi_startproc
movq $0, a(%rip)
xorl %eax, %eax
ret
.cfi_endproc
.LFE0:
.size main, .-main
.local a
.comm a,8,8
.ident "GCC: (GNU) 11.2.0"
.section .note.GNU-stack,"",@progbits
gcc-trunk -v
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20210930 (experimental) (GCC)
gcc-trunk test.c -S -O3
cat test.s
.file "test.c"
.text
.section .text.startup,"ax",@progbits
.p2align 4
.globl main
.type main, @function
main:
.LFB0:
.cfi_startproc
movq a(%rip), %rcx
movq %rcx, %rsi
andl $4294967295, %esi
je .L13
movl $2, %eax
addq $1, %rsi
cqto
idivq %rsi
testb $1, %al
je .L13
testl %ecx, %ecx
je .L17
.L13:
movq $0, a(%rip)
xorl %eax, %eax
ret
.L17:
pushq %rax
.cfi_def_cfa_offset 16
call foo
xorl %edx, %edx
xorl %eax, %eax
movq %rdx, a(%rip)
popq %rcx
.cfi_def_cfa_offset 8
ret
.cfi_endproc
.LFE0:
.size main, .-main
.local a
.comm a,8,8
.ident "GCC: (GNU) 12.0.0 20210930 (experimental)"
.section .note.GNU-stack,"",@progbits
