On Sun, Feb 2, 2025 at 3:33 PM Richard Biener
<richard.guent...@gmail.com> wrote:
>
>
>
> > Am 02.02.2025 um 08:00 schrieb H.J. Lu <hjl.to...@gmail.com>:
> >
> > Don't increase callee-saved register cost by 1000x, which leads to that
> > callee-saved registers aren't used to preserve local variable values
> > across calls, by capping the scale to 300.
>
> > PR rtl-optimization/111673
> > PR rtl-optimization/115932
> > PR rtl-optimization/116028
> > PR rtl-optimization/117081
> > PR rtl-optimization/118497
> > * ira-color.cc (assign_hard_reg): Cap callee-saved register cost
> > scale to 300.
> >
> > Signed-off-by: H.J. Lu <hjl.to...@gmail.com>
> > ---
> > gcc/ira-color.cc | 16 ++++++++++++++--
> > 1 file changed, 14 insertions(+), 2 deletions(-)
> >
> > diff --git a/gcc/ira-color.cc b/gcc/ira-color.cc
> > index 0699b349a1a..707ff188250 100644
> > --- a/gcc/ira-color.cc
> > +++ b/gcc/ira-color.cc
> > @@ -2175,13 +2175,25 @@ assign_hard_reg (ira_allocno_t a, bool retry_p)
> > /* We need to save/restore the hard register in
> > epilogue/prologue. Therefore we increase the cost. */
> > {
> > + int scale;
> > + if (optimize_size)
> > + scale = 1;
> > + else
> > + {
> > + scale = REG_FREQ_FROM_BB (ENTRY_BLOCK_PTR_FOR_FN (cfun));
> > + /* Don't increase callee-saved register cost by 1000x,
> > + which leads to that callee-saved registers aren't
> > + used to preserve local variable values across calls,
> > + by capping the scale to 300. */
> > + if (REG_FREQ_MAX == 1000 && scale == REG_FREQ_MAX)
> > + scale = 300;
>
> That leads to 300 for 1000 but 999 for 999 which is odd. I’d have expected
> to scale this down to [0, 300] or is MAX a magic value?
There are
* The weights for each insn varies from 0 to REG_FREQ_BASE.
This constant does not need to be high, as in infrequently executed
regions we want to count instructions equivalently to optimize for
size instead of speed. */
#define REG_FREQ_MAX 1000
/* Compute register frequency from the BB frequency. When optimizing for size,
or profile driven feedback is available and the function is never executed,
frequency is always equivalent. Otherwise rescale the basic block
frequency. */
#define REG_FREQ_FROM_BB(bb) ((optimize_function_for_size_p (cfun) \
|| !cfun->cfg->count_max.initialized_p ()) \
? REG_FREQ_MAX \
: ((bb)->count.to_frequency (cfun) \
* REG_FREQ_MAX / BB_FREQ_MAX) \
? ((bb)->count.to_frequency (cfun) \
* REG_FREQ_MAX / BB_FREQ_MAX) \
: 1)
1000 is the default. If it isn't 1000, it isn't the default. I only want
to get a more reasonable default scale, instead of 1000. Lower
scale will fail the PR rtl-optimization/111673 test on powerpc64.
> > + }
> > rclass = REGNO_REG_CLASS (hard_regno);
> > add_cost = ((ira_memory_move_cost[mode][rclass][0]
> > + ira_memory_move_cost[mode][rclass][1])
> > * saved_nregs / hard_regno_nregs (hard_regno,
> > mode) - 1)
> > - * (optimize_size ? 1 :
> > - REG_FREQ_FROM_BB (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
> > + * scale;
> > cost += add_cost;
> > full_cost += add_cost;
> > }
> > --
> > 2.48.1
> >
--
H.J.
