On Wed, 27 Jan 2021, Jakub Jelinek wrote:
> On Wed, Jan 27, 2021 at 03:40:38PM +0100, Richard Biener wrote:
> > The following avoids repeatedly turning VALUE RTXen into
> > sth useful and re-applying a constant offset through get_addr
> > via DSE check_mem_read_rtx. Instead perform this once for
> > all stores to be visited in check_mem_read_rtx. This avoids
> > allocating 1.6GB of garbage PLUS RTXen on the PR80960
> > testcase, fixing the memory usage regression from old GCC.
> >
> > Bootstrap and regtest running on x86_64-unknown-linux-gnu, OK?
> >
> > Thanks,
> > Richard.
> >
> > 2021-01-27 Richard Biener <rguent...@suse.de>
> >
> > PR rtl-optimization/80960
> > * dse.c (check_mem_read_rtx): Call get_addr on the
> > offsetted address.
> > ---
> > gcc/dse.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/gcc/dse.c b/gcc/dse.c
> > index c88587e7d94..da0df54a2dd 100644
> > --- a/gcc/dse.c
> > +++ b/gcc/dse.c
> > @@ -2219,6 +2219,11 @@ check_mem_read_rtx (rtx *loc, bb_info_t bb_info)
> > }
> > if (maybe_ne (offset, 0))
> > mem_addr = plus_constant (get_address_mode (mem), mem_addr, offset);
> > + /* Avoid passing VALUE RTXen as mem_addr to canon_true_dependence
> > + which will over and over re-create proper RTL and re-apply the
> > + offset above. See PR80960 where we almost allocate 1.6GB of PLUS
> > + RTXen that way. */
> > + mem_addr = get_addr (mem_addr);
> >
> > if (group_id >= 0)
> > {
>
> Does that result in any changes on how much does DSE optimize?
> I mean, if you do 2 bootstraps/regtests, one with this patch and another one
> without it, and at the end of rest_of_handle_dse dump
> locally_deleted, globally_deleted
> for each CU/function, do you get the same counts except perhaps for dse.c?
So I see no difference for stage2-gcc/*.o dse1/dse2 with/without the
patch but counts are _extremely_ small. Statistics:
70148 dse: local deletions = 0, global deletions = 0
32 dse: local deletions = 0, global deletions = 1
9 dse: local deletions = 0, global deletions = 2
7 dse: local deletions = 0, global deletions = 3
2 dse: local deletions = 0, global deletions = 4
2 dse: local deletions = 0, global deletions = 5
3 dse: local deletions = 0, global deletions = 7
67 dse: local deletions = 1, global deletions = 0
1 dse: local deletions = 1, global deletions = 2
12 dse: local deletions = 2, global deletions = 0
1 dse: local deletions = 24, global deletions = 1
2 dse: local deletions = 3, global deletions = 0
4 dse: local deletions = 4, global deletions = 0
4 dse: local deletions = 6, global deletions = 0
1 dse: local deletions = 7, global deletions = 0
1 dse: local deletions = 8, global deletions = 0
so not sure how much confidence this brings over the analytical
reasoning that it shouldn't make a difference ...
stats on just dse2 are even more depressing (given it's cost)
35123 dse: local deletions = 0, global deletions = 0
2 dse: local deletions = 0, global deletions = 1
20 dse: local deletions = 1, global deletions = 0
1 dse: local deletions = 2, global deletions = 0
1 dse: local deletions = 3, global deletions = 0
1 dse: local deletions = 4, global deletions = 0
Richard.
