Forwarding to list as well. ________________________________________ From: Tamar Christina Sent: Friday, October 28, 2016 10:52:17 AM To: Pat Haugen; Maxim Kuvyrkov Cc: GCC Patches Subject: Re: [PATCH] Fix computation of register limit for -fsched-pressure
Hi Pat, The commit seems to be causing some odd stack spills on aarch64. I've created a new ticket https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78142 Thanks, Tamar ________________________________________ From: gcc-patches-ow...@gcc.gnu.org <gcc-patches-ow...@gcc.gnu.org> on behalf of Pat Haugen <pthau...@linux.vnet.ibm.com> Sent: Tuesday, October 18, 2016 4:07:55 PM To: Maxim Kuvyrkov Cc: GCC Patches Subject: Re: [PATCH] Fix computation of register limit for -fsched-pressure On 10/18/2016 05:31 AM, Maxim Kuvyrkov wrote: >> > I see your point and agree that current code isn't optimal. However, I >> > don't think your patch is accurate either. Consider >> > https://gcc.gnu.org/onlinedocs/gccint/Register-Basics.html and let's >> > assume that FIXED_REGISTERS in class CL is set for a third of the >> > registers, and CALL_USED_REGISTERS is set to "1" for another third of >> > registers. So we have a third available for zero-cost allocation >> > (CALL_USED_REGISTERS-FIXED_REGISTERS), a third available for spill-cost >> > allocation (ALL_REGISTERS-CALL_USED_REGISTERS) and a third non-available >> > (FIXED_REGISTERS). >> > >> > For a non-loop-single-basic-block function we should be targeting only the >> > third of register available at zero-cost -- correct? Yes. This is what is done by the current code, but, apparently, by accident. It seems that the right register count can be obtained with: >> > >> > for (int i = 0; i < ira_class_hard_regs_num[cl]; ++i) >> > - if (call_used_regs[ira_class_hard_regs[cl][i]]) >> > - ++call_used_regs_num[cl]; >> > + if (!call_used_regs[ira_class_hard_regs[cl][i]] >> > + || fixed_regs[ira_class_hard_regs[cl][i]]) >> > + ++call_saved_regs_num[cl]; >> > >> > Does this look correct to you? > Thinking some more, it seems like fixed_regs should not be available to the > scheduler no matter what. Therefore, the number of fixed registers should be > subtracted from ira_class_hard_regs_num[cl] without any scaling (entry_freq / > bb_freq). Ahh, yes, I forgot about FIXED_REGISTERS being included in CALL_USED_REGISTERS. I agree they should be totally removed from the register limit calculation. I'll rework the patch. Thanks, Pat
