https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77498
--- Comment #11 from Thomas Preud'homme <thopre01 at gcc dot gnu.org> ---
(In reply to Thomas Preud'homme from comment #9)
> Sadly I could not come up with a minimal testcase so far. What I can see
> from the code is that tree code hoisting increases the live range of some
> values which then translates into more spilling in reload.
>
> As an approximation I'm wondering if the maximum distance (computer in
> number of blocks traversed) from the definition to the use could be used to
> limit when the optimization is applied when optimizing for speed.
I finally managed. The bug can be reproduced by building the following for
arm-none-eabi with -S -O2 -mcpu=cortex-m7 and looking for the push in the
resulting assembly code.
fn1() {
char *a;
char b;
for (; *a; a++) {
if (b)
a++;
fn2();
}
}
With -O2: r3, r4, r5 and lr and pushed.
With -O2 -fno-code-hoisting: r4 and lr are pushed only.
Similarly for -mcpu=cortex-m0plus:
enum { ENUM1, ENUM2, ENUM3 } a;
fn1() {
char *b;
for (; *b && a != ENUM2; b++)
switch (a) {
case ENUM1: a = ENUM3;
}
}
