| Issue |
156251
|
| Summary |
_BitInt division with -Oz produces much larger code than -O0, and compiles slow
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
neldredge
|
Using Clang 21.1.0 targeting x86_64-pc-linux-gnu and the following program:
```
typedef unsigned _BitInt(8192) T;
T div(T a, T b) {
return a/b;
}
```
Using `-Oz` produces much larger code than with `-O0` (and also takes a long time to compile).
```
nate@tractrix /tmp $ time clang -c -Oz -std=c23 -target x86_64-pc-linux-gnu bitint.c
real 0m13.015s
user 0m12.935s
sys 0m0.043s
nate@tractrix /tmp $ size bitint.o
text data bss dec hex filename
975795 0 0 975795 ee3b3 bitint.o
nate@tractrix /tmp $ time clang -c -O0 -std=c23 -target x86_64-pc-linux-gnu bitint.c
real 0m0.172s
user 0m0.143s
sys 0m0.027s
nate@tractrix /tmp $ size bitint.o
text data bss dec hex filename
138973 0 0 138973 21edd bitint.o
```
With `_BitInt(65536)`,`-Oz` didn't finish after 5 minutes, while every other level including `-Os` and `-O3` completed in about 20-30 seconds.
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