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* [Bug tree-optimization/100188] New: missed optimization for dead code elimination at -O3 (vs. -O1)
@ 2021-04-21 16:44 zhendong.su at inf dot ethz.ch
2021-04-22 7:39 ` [Bug ipa/100188] " rguenth at gcc dot gnu.org
2023-08-18 1:52 ` pinskia at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: zhendong.su at inf dot ethz.ch @ 2021-04-21 16:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100188
Bug ID: 100188
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: ---
[529] % 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 20210421 (experimental) [master revision
7f9b7ccf0c1:344da81f015:5445da1a94bb4df752209e54f4aa21702609a20a] (GCC)
[530] %
[530] % gcctk -O1 -S -o O1.s small.c
[531] % gcctk -O3 -S -o O3.s small.c
[532] %
[532] % wc O1.s O3.s
14 31 324 O1.s
35 72 615 O3.s
49 103 939 total
[533] %
[533] % grep foo O1.s
[534] % grep foo O3.s
jmp foo
[535] %
[535] % cat small.c
extern void foo(void);
static int b = 1, c, *f;
static int a() { return 0; }
static void d(int j) {
int g, *h[36] = {&g, &g}, **i[1] = {&h[0]};
if (!j) {
c = 0;
foo();
}
}
int main() {
int k[8];
d(b);
if (a())
f = &k[0];
return 0;
}
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2021-04-21 16:44 [Bug tree-optimization/100188] New: missed optimization for dead code elimination at -O3 (vs. -O1) zhendong.su at inf dot ethz.ch
2021-04-22 7:39 ` [Bug ipa/100188] " rguenth at gcc dot gnu.org
2023-08-18 1:52 ` pinskia at gcc dot gnu.org
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