[Bug rtl-optimization/63191] New: 32-bit gcc uses excessive memory during dead store elimination with -fPIC

["woodfin at intersystems dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63191

            Bug ID: 63191
           Summary: 32-bit gcc uses excessive memory during dead store
                    elimination with -fPIC
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: woodfin at intersystems dot com

Created attachment 33453
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33453&action=edit
Source triggering memory usage

Every version of gcc I try from 4.4 -> 4.9.1 on 32-bit Linux uses excessive
memory (eventually exhausting all 3GB of virtual address space) when I compile
the attached (generated, simplified) source with

g++ -c -O2 -fPIC badmatch.cpp

4.3 does not exhibit the issue.

64-bit Linux (gcc 4.4.4 in that case) does not exhibit the issue, and memory
usage tops out at ~440MB. gcc 4.4.4 on 32-bit Linux does exhibit the issue.

Dropping -fPIC causes memory usage to top out at ~175MB and the compile to
succeed.

-no-dse eliminates the problem as well.

A look at the mallocs in the debugger suggests that the explosion of
allocations is happening under rest_of_handle_dse(), e.g.:

#0  0x00332e46 in malloc () from /lib/libc.so.6
#1  0x08a26148 in xmalloc ()
#2  0x0829285b in pool_alloc(alloc_pool_def*) () at
../.././gcc/alloc-pool.c:281
#3  0x082f076e in cselib_lookup(rtx_def*, machine_mode, int, machine_mode) ()
at ../.././gcc/cselib.c:1303
#4  0x089536e2 in canon_address(rtx_def*, int*, int*, long long*, cselib_val**)
() at ../.././gcc/dse.c:1182
#5  0x08954770 in record_store(rtx_def*, bb_info*) () at ../.././gcc/dse.c:1443
#6  0x08955e6a in rest_of_handle_dse() () at ../.././gcc/dse.c:2616
#7  0x084bd923 in execute_one_pass(opt_pass*) () at ../.././gcc/passes.c:2233

The most recent version with which I have tested:

>g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/nethome/woodfin/opt/lnxrhx86/gcc-4.9.1/libexec/gcc/i686-pc-linux-gnu/4.9.1/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ./configure --prefix=/nethome/woodfin/opt/lnxrhx86/gcc-4.9.1
--enable-languages=c,c++ --with-mpfr=/nethome/woodfin/opt/lnxrhx86/mpfr-2.4.2
--with-gmp=/nethome/woodfin/opt/lnxrhx86/gmp-4.3.2
--with-mpc=/nethome/woodfin/opt/lnxrhx86/mpc-1.0.2
Thread model: posix
gcc version 4.9.1 (GCC)