On Thu, May 2, 2013 at 1:16 PM, Richard Biener <richard.guent...@gmail.com> wrote: > On Wed, May 1, 2013 at 5:11 PM, Nikhil Patil <nikhilpatil3...@gmail.com> > wrote: >> On Tue, Apr 30, 2013 at 1:32 PM, Richard Biener >> <richard.guent...@gmail.com> wrote: >>> On Mon, Apr 29, 2013 at 7:34 PM, Nikhil Patil <nikhilpatil3...@gmail.com> >>> wrote: >>>> Hello, >>>> >>>> 1. Which passes of gcc make use of points-to information in >>>> SSA_NAME_PTR_INFO (or more precisely, pt_solution) in doing >>>> optimizations? >>> >>> All passes that query the alias oracle (tree-ssa-alias.h) which is almost >>> all passes doing optimization of memory accesses. >> >> Thanks a lot for giving direction. I will try finding the passes. >> >>> >>>> >>>> 2. Also, who computes this points-to information and populates >>>> pt_solution? Is it ONLY ipa-pta pass? >>> >>> It is points-to analysis, both the IPA variant and the local variant >>> (ealias and alias >>> passes). >> >> From what I could understand, gimple passes "pass_build_ealias" >> (ealias) and "pass_build_alias" (alias) flags "TODO_rebuild_alias" at >> end and then function "execute_function_todo" from passes.c calls >> "compute_may_aliases ()" which eventually computes points-to >> information. > > Correct. > >> Then the IPA PTA pass finds a more precise points-to information. >> Please correct if I am wrong. > > Well. The IPA PTA pass is supposed to compute a points-to solution > for the whole translation unit, thus it should be more precise. Due to > limitations and bugs in IPA PTA the result does not necessarily have to > be more precise. > > I do not consider the current IPA PTA code production ready (it does > not scale very well and it doesn't result in any performance improvements > for SPEC 2k6). > > It's a long-time item on my personal TODO list to at least address the > fundamental problems with the current implementation (read: bugs). > But my TODO list is quite crowded ...
Thanks a lot. The discussion gave me a more insight into the topic and solved my doubts. > > Richard. > >>> >>>> When I accessed pt_solution through a plugin which REPLACES ipa-pta >>>> pass, I found that the information (in pt_solution) with and without >>>> ipa-pta pass differs only in terms of flags in pt_solution. Here with >>>> the examples I could construct, I found that the bitmap 'vars' in >>>> pt_solution is same for both the cases. Is it always true? >>> >>> In theory IPA PTA should be able to compute a more precise solution, >>> thus have different (less) bits set in 'vars'. There are several testcases >>> that show this, look for ipa-pta* testcases in gcc/testsuite/ >>> >>> Richard. >>> >>>> Can someone please help in clarifying these doubts. >>>> >>>> Thanks in advance. >>>> >>>> -- >>>> Regards, >>>> Nikhil Patil. >> >> -- >> Regards, >> Nikhil Patil. -- Regards, Nikhil Patil.
