On Fri, Feb 14, 2014 at 3:50 AM, dxq <ziya...@163.com> wrote: > Richard Biener-2 wrote >> On Sat, Feb 8, 2014 at 8:29 AM, dxq < > >> ziyan01@ > >> > wrote: >>> hi all, >>> >>> We found that gcc would run out of memory on Windows when compiling a >>> *big* >>> function (100000 lines). >>> >>> More investigation shows that gcc crashes at the function >>> *compute_avail*, >>> in tree-fre pass. *compute_avail* collects information from basic >>> blocks, >>> so memory is allocated to record informantion. >>> However, if there are huge number of basic blocks, the memory would be >>> exhausted and gcc would crash down, especially for Windows PC, only 2G or >>> 4G >>> memory generally. It's ok On linux, and *compute_avail* allocates *2.4G* >>> memory. I guess some optimization passes in gcc like FRE didn't consider >>> the >>> extreme >>> case. >> >> This was fixed for GCC 4.8, FRE no longer uses compute_avail (but PRE >> still does). >> Basically GCC 4.8 should (at -O1) compile most extreme cases just fine. >> >> Richard. > > hi, Richard, > > More investigation shows that > 1, loop related passes take more compiling time and memory, especially > pass_rtl_move_loop_invariants, lim, > and at least lim on tree will impact a lot to the following passes. > 2, ira will take more than 20g memory in function *create_loop_tree_nodes*, > because ira chooses 'mixed' > or 'all' region when optimize level. > 3, sms pass always creats ddgs for all loops in compiled function, then does > sms optimization for all loops, > and finally frees ddgs. If there are huge number of loops, sms may crash > when creating ddgs because of > running out of memory. > > The passes above , should someone confirm about memory pressure problem?
What compiler version did you check? I think that 4.8 has improvements for 1. and 2. (SMS is unmaintained). Note that we only spent time to make -O1 behave sanely with extremely large functions. Finally I'd suggest you open a bugreport and attach a testcase to it that exposes the issues you list. Richard. > Thanks for your reply! > > danxiaoqiang > > > > -- > View this message in context: > http://gcc.1065356.n5.nabble.com/FRE-may-run-out-of-memory-tp1009578p1011035.html > Sent from the gcc - patches mailing list archive at Nabble.com.
