[Bug tree-optimization/100314] New: missed optimization for dead code elimination at -O3 (vs. -O1)
zhendong.su at inf dot ethz.ch
gcc-bugzilla@gcc.gnu.org
Wed Apr 28 10:17:26 GMT 2021
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100314
Bug ID: 100314
Summary: missed optimization for dead code elimination at -O3
(vs. -O1)
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: zhendong.su at inf dot ethz.ch
Target Milestone: ---
[592] % gcctk -v
Using built-in specs.
COLLECT_GCC=gcctk
COLLECT_LTO_WRAPPER=/local/suz-local/software/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --disable-bootstrap
--prefix=/local/suz-local/software/local/gcc-trunk --enable-languages=c,c++
--disable-werror --enable-multilib --with-system-zlib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210428 (experimental) [master revision
852dd866e2f:9b04e5b2651:b81e2d5e76a6bcc71f45b122e8b5538ddb7ebf4c] (GCC)
[593] %
[593] % gcctk -O1 -S -o O1.s small.c
[594] % gcctk -O3 -S -o O3.s small.c
[595] %
[595] % wc O1.s O3.s
21 45 392 O1.s
42 86 686 O3.s
63 131 1078 total
[596] %
[596] % grep foo O1.s
[597] % grep foo O3.s
jmp foo
[598] %
[598] % cat small.c
extern void foo(void);
static int a, *c, g, **j;
int b;
static void e() {
int k, *l[5] = {&k, &k, &k, &k, &k};
while (g) {
j = &l[0];
b++;
}
}
static void d(int m) {
int **h[30] = {&c}, ***i[1] = {&h[3]};
if (m)
foo();
e();
}
int main() {
d(a);
return 0;
}
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