On Sat, Aug 29, 2026 at 11:18 AM Jeff Law <[email protected]> wrote:
>
>
> On 8/19/26 9:04 AM, Jovan Dmitrovic wrote:
> > Currently, ivopt calculates register pressure cost so that the cost of
> > spilling induction variables is exactly double the cost of spilling
> > loop invariants, which is not exactly right.
> > When invariants are spilled, only loading the invariant back to
> > registers should be taken into account, as we don't need to save them
> > more than once. This isn't the case for IV candidates which have to
> > be both loaded and stored for each iteration of the loop.
> >
> > gcc/ChangeLog:
> >
> > * tree-ssa-loop-ivopts.cc (ivopts_estimate_reg_pressure):
> > Change register pressure estimate in order to respect
> > the impact of spilling induction variables, compared
> > to spilling loop invariants.
> >
> > Co-authored-by: Radosav Krunić <[email protected]>
> > Signed-off-by: Djordje Todorović <[email protected]>
> > Signed-off-by: Chao-Ying Fu <[email protected]>
> > Signed-off-by: Jovan Dmitrović <[email protected]>
> > Signed-off-by: Radosav Krunić <[email protected]>
> > ---
>
> I've pushed this one as well. Thanks.
Except this one broke bootstrap.
/home/apinski/src/upstream-gcc-new/gcc/gcc/tree-ssa-loop-ivopts.cc:6109:73:
error: statement has no effect [-Werror=unused-value]
6109 | + target_spill_cost[speed] * (n_cands -
available_regs) / 2;
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
The patch does:
+ cost = target_spill_cost [speed] * (regs_needed - available_regs) / 2;
+ + target_spill_cost[speed] * (n_cands - available_regs) / 2;
Since there is a semi-colon before the plus sign, the second part of
the expression is unused.
The plus becomes an unary operator +. So the whole second part of what
looks like the full expression goes unused.
Thanks,
Andrea
>
>
> jeff
>
