| Issue |
183132
|
| Summary |
byte copy loop folds at -Os -O2 -Og but not -Oz
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
ZERICO2005
|
https://godbolt.org/z/MK7bbrehq
```c
// https://github.com/charlesnicholson/nanoprintf/blob/47af8e576556d7be9621f431e442123eccc056d3/nanoprintf.h#L566
uint64_t npf_double_to_int_rep(double f) {
// Union-cast is UB pre-C11 and in all C++; the compiler optimizes the code below.
uint64_t bin;
char const *src = "" const *)&f;
char *dst = (char *)&bin;
for (uint_fast8_t i = 0; i < sizeof(f); ++i) { dst[i] = src[i]; }
return bin;
}
```
A loop is emitted for this code at `-Oz`. `-O1 -O2 -O3 -Os` emit a bitcast, and `-Og` produces different code, but critically it does not have any loops like `-Oz` does.
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