On 12-10-13 9:40 AM, Steven Bosscher wrote:
Hello,
This fixes the long-standing enhancement request to use DF_LIVE in
IRA. To quote the first comment in the PR:
IRA should be using the DF-LIVE sets, which are smaller than the DF-LR
sets when they are available (typically at O2 and above). The proper
sets can be conveniently accessed using the df_get_live_[in,out]
functions which use DF-LIVE if it is available and fall back to DF-LR
if it is not.
I thought that DF_LIVE wasn't available at -O1 in IRA, but
interestingly ira.c:ira() adds it to the DF-problems list in that case
already:
$ grep -C3 -n df_live_add ira.c
4160-
4161- if (optimize == 1)
4162- {
4163: df_live_add_problem ();
4164- df_live_set_all_dirty ();
4165- }
4166-#ifdef ENABLE_CHECKING
So DF_LIVE is already being computed for IRA. It's just not being used
because the DF_LR_{IN,OUT} macros are used instead of the
df_get_live_{in,out} functions. With my patch, the DF_LIVE sets are
used, which results in marginally faster compile times for my set of
cc1-i files on power64 and on x86_64, as well as smaller code. There's
also a good speedup for the PR54146 test case.
Only reload.c still uses the DF_LR_OUT. The comment in
find_dummy_reload() suggests this is intentional.
I also fond a bug in IRA:
4392- touch the artificial uses and defs. */
4393- df_finish_pass (true);
4394- if (optimize > 1)
4395: df_live_add_problem ();
4396- df_scan_alloc (NULL);
4397- df_scan_blocks ();
4398-
At optimize>1 the DF_LIVE problem is already always computed. I think
the idea here was to *remove* the DF_LIVE problem at -O1, which is
also part of the attached patch.
(Perhaps we should even simply not add the DF_LIVE problem at -O1, but
that can be done in a follow-up patch if necessary.)
Bootstrapped and tested (with default checking and with release
checking) on powerpc64-unknown-linux-gnu and x86_64-unknown-linux-gnu.
OK for trunk?
LIVE is not used on purpose. I added LIVE usage to the old RA about 10
years ago (it was before DF-infrastructure). Everything was ok until,
somebody reported compiler crash on semantically wrong program
(something with usage of uninitialized variable). After that I removed
this code.
Probably, that is also a reason why reload uses LR not LIVE. So I'd
like to wait a few weeks. When I have more time, I am going to
reproduce this test suite and look how IRA behaves on it.
Thanks, Steven.
