https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91817
Bug ID: 91817
Summary: compile with -O3 is more-than-expectedly slower than
-O2
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: hehaochen at hotmail dot com
Target Milestone: ---
Created attachment 46898
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46898&action=edit
this test case is from gcc-45364
### This is normal in GCC 5.3.1(Docker version): ###
root@ubuntu:/home/jxl# time gcc -m32 -o1 -g -c 1.i -o test.o
real 0m1.017s
user 0m0.876s
sys 0m0.072s
root@ubuntu:/home/jxl# time gcc -m32 -o2 -g -c 1.i -o test.o
real 0m1.250s
user 0m0.864s
sys 0m0.064s
root@ubuntu:/home/jxl# time gcc -m32 -o3 -g -c 1.i -o test.o
real 0m4.446s
user 0m0.700s
sys 0m0.476s
### HOWEVER, it is extremely slow in GCC 4.6(Docker version): ###
root@4beb8027e1fb:/# time gcc -m32 -o1 -g -c 1.i -o test.o
real 0m3.066s
user 0m0.656s
sys 0m0.772s
root@4beb8027e1fb:/# time gcc -m32 -o2 -g -c 1.i -o test.o
real 0m1.112s
user 0m0.796s
sys 0m0.156s
root@4beb8027e1fb:/# time gcc -m32 -O3 -g -c 1.i -o test.o
real 2m55.363s
user 2m41.224s
sys 0m1.908s
###### Root cause locates in "var-tracking dataflow" ######
root@4beb8027e1fb:/# gcc -m32 -O3 -ftime-report -g -c 1.i -o test.o
Execution times (seconds)
callgraph construction: 0.00 ( 0%) usr 0.01 ( 0%) sys 0.01 ( 0%) wall
1432 kB ( 1%) ggc
callgraph optimization: 0.02 ( 0%) usr 0.00 ( 0%) sys 0.02 ( 0%) wall
137 kB ( 0%) ggc
ipa function splitting: 0.00 ( 0%) usr 0.00 ( 0%) sys 0.03 ( 0%) wall
528 kB ( 1%) ggc
ipa pure const : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
25 kB ( 0%) ggc
ipa SRA : 0.00 ( 0%) usr 0.01 ( 0%) sys 0.01 ( 0%) wall
405 kB ( 0%) ggc
cfg cleanup : 0.08 ( 0%) usr 0.01 ( 0%) sys 0.11 ( 0%) wall
549 kB ( 1%) ggc
trivially dead code : 0.03 ( 0%) usr 0.00 ( 0%) sys 0.06 ( 0%) wall
0 kB ( 0%) ggc
df scan insns : 0.03 ( 0%) usr 0.01 ( 0%) sys 0.04 ( 0%) wall
6 kB ( 0%) ggc
df multiple defs : 0.02 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
0 kB ( 0%) ggc
df reaching defs : 0.12 ( 0%) usr 0.02 ( 1%) sys 0.12 ( 0%) wall
0 kB ( 0%) ggc
df live regs : 0.35 ( 0%) usr 0.01 ( 0%) sys 0.35 ( 0%) wall
0 kB ( 0%) ggc
df live&initialized regs: 0.20 ( 0%) usr 0.01 ( 0%) sys 0.25 ( 0%) wall
0 kB ( 0%) ggc
df use-def / def-use chains: 0.04 ( 0%) usr 0.02 ( 1%) sys 0.07 ( 0%)
wall 0 kB ( 0%) ggc
df live reg subwords : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.00 ( 0%) wall
0 kB ( 0%) ggc
df reg dead/unused notes: 0.10 ( 0%) usr 0.00 ( 0%) sys 0.08 ( 0%) wall
585 kB ( 1%) ggc
register information : 0.05 ( 0%) usr 0.00 ( 0%) sys 0.03 ( 0%) wall
0 kB ( 0%) ggc
alias analysis : 0.08 ( 0%) usr 0.00 ( 0%) sys 0.08 ( 0%) wall
2860 kB ( 3%) ggc
alias stmt walking : 0.11 ( 0%) usr 0.06 ( 2%) sys 0.17 ( 0%) wall
8 kB ( 0%) ggc
register scan : 0.00 ( 0%) usr 0.00 ( 0%) sys 0.03 ( 0%) wall
9 kB ( 0%) ggc
rebuild jump labels : 0.02 ( 0%) usr 0.01 ( 0%) sys 0.00 ( 0%) wall
0 kB ( 0%) ggc
preprocessing : 0.07 ( 0%) usr 0.35 (14%) sys 0.45 ( 0%) wall
3387 kB ( 3%) ggc
lexical analysis : 0.19 ( 0%) usr 0.57 (23%) sys 0.74 ( 0%) wall
0 kB ( 0%) ggc
parser : 0.13 ( 0%) usr 0.47 (19%) sys 0.72 ( 0%) wall
18502 kB (18%) ggc
inline heuristics : 0.02 ( 0%) usr 0.01 ( 0%) sys 0.01 ( 0%) wall
133 kB ( 0%) ggc
integration : 0.07 ( 0%) usr 0.05 ( 2%) sys 0.14 ( 0%) wall
8467 kB ( 8%) ggc
tree gimplify : 0.02 ( 0%) usr 0.00 ( 0%) sys 0.03 ( 0%) wall
4760 kB ( 5%) ggc
tree CFG construction : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
1460 kB ( 1%) ggc
tree CFG cleanup : 0.04 ( 0%) usr 0.02 ( 1%) sys 0.11 ( 0%) wall
318 kB ( 0%) ggc
tree VRP : 0.10 ( 0%) usr 0.04 ( 2%) sys 0.14 ( 0%) wall
2898 kB ( 3%) ggc
tree copy propagation : 0.02 ( 0%) usr 0.01 ( 0%) sys 0.02 ( 0%) wall
197 kB ( 0%) ggc
tree PTA : 0.07 ( 0%) usr 0.02 ( 1%) sys 0.06 ( 0%) wall
582 kB ( 1%) ggc
tree SSA rewrite : 0.05 ( 0%) usr 0.01 ( 0%) sys 0.05 ( 0%) wall
1884 kB ( 2%) ggc
tree SSA other : 0.02 ( 0%) usr 0.01 ( 0%) sys 0.03 ( 0%) wall
17 kB ( 0%) ggc
tree SSA incremental : 0.06 ( 0%) usr 0.01 ( 0%) sys 0.08 ( 0%) wall
706 kB ( 1%) ggc
tree operand scan : 0.05 ( 0%) usr 0.09 ( 4%) sys 0.13 ( 0%) wall
4319 kB ( 4%) ggc
dominator optimization: 0.05 ( 0%) usr 0.01 ( 0%) sys 0.03 ( 0%) wall
1525 kB ( 1%) ggc
tree CCP : 0.06 ( 0%) usr 0.01 ( 0%) sys 0.06 ( 0%) wall
321 kB ( 0%) ggc
tree split crit edges : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
589 kB ( 1%) ggc
tree reassociation : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
194 kB ( 0%) ggc
tree PRE : 0.06 ( 0%) usr 0.05 ( 2%) sys 0.10 ( 0%) wall
561 kB ( 1%) ggc
tree FRE : 0.08 ( 0%) usr 0.03 ( 1%) sys 0.09 ( 0%) wall
125 kB ( 0%) ggc
tree code sinking : 0.02 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
98 kB ( 0%) ggc
tree forward propagate: 0.03 ( 0%) usr 0.02 ( 1%) sys 0.03 ( 0%) wall
293 kB ( 0%) ggc
tree conservative DCE : 0.02 ( 0%) usr 0.04 ( 2%) sys 0.04 ( 0%) wall
34 kB ( 0%) ggc
tree aggressive DCE : 0.04 ( 0%) usr 0.01 ( 0%) sys 0.05 ( 0%) wall
738 kB ( 1%) ggc
tree DSE : 0.00 ( 0%) usr 0.00 ( 0%) sys 0.02 ( 0%) wall
118 kB ( 0%) ggc
PHI merge : 0.00 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
241 kB ( 0%) ggc
tree loop invariant motion: 0.01 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%)
wall 0 kB ( 0%) ggc
scev constant prop : 0.00 ( 0%) usr 0.01 ( 0%) sys 0.00 ( 0%) wall
206 kB ( 0%) ggc
complete unrolling : 0.00 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
779 kB ( 1%) ggc
tree slp vectorization: 0.03 ( 0%) usr 0.00 ( 0%) sys 0.03 ( 0%) wall
1833 kB ( 2%) ggc
tree loop distribution: 0.02 ( 0%) usr 0.00 ( 0%) sys 0.02 ( 0%) wall
3 kB ( 0%) ggc
tree iv optimization : 0.04 ( 0%) usr 0.02 ( 1%) sys 0.04 ( 0%) wall
2413 kB ( 2%) ggc
tree copy headers : 0.00 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
227 kB ( 0%) ggc
tree SSA uncprop : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
0 kB ( 0%) ggc
dominance computation : 0.04 ( 0%) usr 0.00 ( 0%) sys 0.05 ( 0%) wall
0 kB ( 0%) ggc
out of ssa : 0.02 ( 0%) usr 0.00 ( 0%) sys 0.02 ( 0%) wall
12 kB ( 0%) ggc
expand vars : 0.02 ( 0%) usr 0.00 ( 0%) sys 0.00 ( 0%) wall
957 kB ( 1%) ggc
expand : 0.07 ( 0%) usr 0.00 ( 0%) sys 0.07 ( 0%) wall
8481 kB ( 8%) ggc
varconst : 0.01 ( 0%) usr 0.01 ( 0%) sys 0.00 ( 0%) wall
1 kB ( 0%) ggc
forward prop : 0.03 ( 0%) usr 0.00 ( 0%) sys 0.08 ( 0%) wall
539 kB ( 1%) ggc
CSE : 0.09 ( 0%) usr 0.01 ( 0%) sys 0.11 ( 0%) wall
87 kB ( 0%) ggc
dead code elimination : 0.05 ( 0%) usr 0.00 ( 0%) sys 0.04 ( 0%) wall
0 kB ( 0%) ggc
dead store elim1 : 0.04 ( 0%) usr 0.01 ( 0%) sys 0.07 ( 0%) wall
554 kB ( 1%) ggc
dead store elim2 : 0.07 ( 0%) usr 0.00 ( 0%) sys 0.06 ( 0%) wall
600 kB ( 1%) ggc
loop invariant motion : 0.26 ( 0%) usr 0.00 ( 0%) sys 0.26 ( 0%) wall
0 kB ( 0%) ggc
loop unswitching : 0.25 ( 0%) usr 0.00 ( 0%) sys 0.26 ( 0%) wall
0 kB ( 0%) ggc
CPROP : 0.13 ( 0%) usr 0.00 ( 0%) sys 0.12 ( 0%) wall
1555 kB ( 1%) ggc
PRE : 0.10 ( 0%) usr 0.00 ( 0%) sys 0.10 ( 0%) wall
145 kB ( 0%) ggc
CSE 2 : 0.06 ( 0%) usr 0.00 ( 0%) sys 0.06 ( 0%) wall
40 kB ( 0%) ggc
branch prediction : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
242 kB ( 0%) ggc
combiner : 0.11 ( 0%) usr 0.00 ( 0%) sys 0.08 ( 0%) wall
1475 kB ( 1%) ggc
if-conversion : 0.02 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
385 kB ( 0%) ggc
regmove : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
0 kB ( 0%) ggc
integrated RA : 0.21 ( 0%) usr 0.00 ( 0%) sys 0.23 ( 0%) wall
1278 kB ( 1%) ggc
reload : 0.10 ( 0%) usr 0.00 ( 0%) sys 0.14 ( 0%) wall
379 kB ( 0%) ggc
reload CSE regs : 0.12 ( 0%) usr 0.01 ( 0%) sys 0.15 ( 0%) wall
1568 kB ( 1%) ggc
load CSE after reload : 0.02 ( 0%) usr 0.00 ( 0%) sys 0.00 ( 0%) wall
6 kB ( 0%) ggc
thread pro- & epilogue: 0.02 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
128 kB ( 0%) ggc
peephole 2 : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
236 kB ( 0%) ggc
hard reg cprop : 0.02 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
3 kB ( 0%) ggc
scheduling 2 : 0.11 ( 0%) usr 0.00 ( 0%) sys 0.11 ( 0%) wall
43 kB ( 0%) ggc
machine dep reorg : 0.01 ( 0%) usr 0.00 ( 0%) sys 0.02 ( 0%) wall
46 kB ( 0%) ggc
reorder blocks : 0.04 ( 0%) usr 0.00 ( 0%) sys 0.02 ( 0%) wall
1016 kB ( 1%) ggc
reg stack : 0.00 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
6 kB ( 0%) ggc
final : 0.07 ( 0%) usr 0.00 ( 0%) sys 0.05 ( 0%) wall
1040 kB ( 1%) ggc
symout : 0.06 ( 0%) usr 0.04 ( 2%) sys 0.10 ( 0%) wall
12092 kB (12%) ggc
variable tracking : 0.32 ( 0%) usr 0.01 ( 0%) sys 0.32 ( 0%) wall
2201 kB ( 2%) ggc
var-tracking dataflow : 157.01 (96%) usr 0.32 (13%) sys 158.01 (95%) wall
0 kB ( 0%) ggc
var-tracking emit : 1.39 ( 1%) usr 0.01 ( 0%) sys 1.40 ( 1%) wall
726 kB ( 1%) ggc
rest of compilation : 0.04 ( 0%) usr 0.00 ( 0%) sys 0.15 ( 0%) wall
565 kB ( 1%) ggc
remove unused locals : 0.08 ( 0%) usr 0.00 ( 0%) sys 0.06 ( 0%) wall
0 kB ( 0%) ggc
address taken : 0.00 ( 0%) usr 0.01 ( 0%) sys 0.02 ( 0%) wall
0 kB ( 0%) ggc
unaccounted todo : 0.08 ( 0%) usr 0.00 ( 0%) sys 0.04 ( 0%) wall
0 kB ( 0%) ggc
rebuild frequencies : 0.02 ( 0%) usr 0.00 ( 0%) sys 0.00 ( 0%) wall
94 kB ( 0%) ggc
repair loop structures: 0.00 ( 0%) usr 0.00 ( 0%) sys 0.01 ( 0%) wall
72 kB ( 0%) ggc
TOTAL : 163.80 2.46 167.08
104717 kB
