On 13/02/13 23:35, Vladimir Makarov wrote: > On 13-02-07 2:11 PM, Tom de Vries wrote: >> Vladimir, >> >> On 25/01/13 16:36, Vladimir Makarov wrote: >>> On 01/25/2013 08:05 AM, Tom de Vries wrote: >>>> Vladimir, >>>> >>>> this patch adds analysis of register usage of functions for usage by IRA. >>>> >>>> The patch: >>>> - adds analysis in pass_final to track which hard registers are set or >>>> clobbered >>>> by the function body, and stores that information in a struct >>>> cgraph_node. >>>> - adds a target hook fn_other_hard_reg_usage to list hard registers that >>>> are >>>> set or clobbered by a call to a function, but are not listed as such >>>> in the >>>> function body, such as f.i. registers clobbered by veneers inserted by >>>> the >>>> linker. >>>> - adds a reg-note REG_CALL_DECL, to be able to easily link call_insns to >>>> their >>>> corresponding declaration, even after the calls may have been split >>>> into an >>>> insn (set register to function address) and a call_insn (call >>>> register), which >>>> can happen for f.i. sh, and mips with -mabi-calls. >>>> - uses the register analysis in IRA. >>>> - adds an option -fuse-caller-save to control the optimization, on by >>>> default >>>> at -Os and -O2 and higher. >> <SNIP> >> >>>> Bootstrapped and reg-tested on x86_64, Ada inclusive. Build and reg-tested >>>> on >>>> mips, arm, ppc and sh. No issues found. OK for stage1 trunk? >>>> >>>> >>> Thanks for the patch. I'll look at it during the next week. >>> >> Did you get a chance to look at this? > Sorry for the delay with the answer. I was and am quite busy with other > more urgent things. I'll work on it when I have more free time. In any > case, I'll do it before stage1 to have your patch ready.
Vladimir, do you have an ETA on this review? >>> Right now I see that the code is based on reload which uses >>> caller-saves.c. LRA does not use caller-saves.c at all. Right now we >>> have LRA support only for x86/x86-64 but the next version will probably >>> have a few more targets based on LRA. Fortunately, LRA modification >>> will be pretty easy with all this machinery. >>> >> I see, thanks for noticing that. Btw I'm now working on a testsuite construct >> dg-size-compare to be able to do >> dg-size-compare "text" "-fuse-caller-save" "<" "-fno-use-caller-save" >> which I could have used to create a generic testcase, which would have >> demonstrated that the optimization didn't work for x86_64. > I thought about implementing your optimization for LRA by myself. But it > is ok if you decide to work on it. At least, I am not going to start > this work for a month. >> I'm also currently looking at how to use the analysis in LRA. >> AFAIU, in lra-constraints.c we do a backward scan over the insns, and keep >> track >> of how many calls we've seen (calls_num), and mark insns with that number. >> Then >> when looking at a live-range segment consisting of a def or use insn a and a >> following use insn b, we can compare the number of calls seen for each insn, >> and >> if they're not equal there is at least one call between the 2 insns, and if >> the >> corresponding hard register is clobbered by calls, we spill after insn a and >> restore before insn b. >> >> That is too coarse-grained to use with our analysis, since we need to know >> which >> calls occur in between insn a and insn b, and more precisely which registers >> those calls clobbered. > >> I wonder though if we can do something similar: we keep an array >> call_clobbers_num[FIRST_PSEUDO_REG], initialized at 0 when we start scanning. >> When encountering a call, we increase the call_clobbers_num entries for the >> hard >> registers clobbered by the call. >> When encountering a use, we set the call_clobbers_num field of the use to >> call_clobbers_num[reg_renumber[original_regno]]. >> And when looking at a live-range segment, we compare the clobbers_num field >> of >> insn a and insn b, and if it is not equal, the hard register was clobbered >> by at >> least one call between insn a and insn b. >> Would that work? WDYT? >> > As I understand you looked at live-range splitting code in > lra-constraints.c. To get necessary info you should look at ira-lives.c. Unfortunately I haven't been able to find time to work further on the LRA part. So if you're still willing to pick up that part, that would be great. Thanks, - Tom
