[Bug lto/50165] New: [4.7 regression] Huge build time regression (Firefox lto build)

["markus at trippelsdorf dot de" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50165

             Bug #: 50165
           Summary: [4.7 regression] Huge build time regression (Firefox
                    lto build)
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: markus@trippelsdorf.de
                CC: dnovillo@google.com


Since Diegos patches (rev. 177571, 177661, 177704) went in
lto1 seems to run forever (I've killed it after 40 minutes) when libxul
is linked during a Firefox LTO build. 
It used to finish in 4-5 minutes before.

This is a profile captured during the lto1 run:
("perf record -ag sleep 5" and then "perf report -v -g --stdio")

 # Events: 5K cycles
#
# Overhead          Command                                    Shared Object   
                                                  Symbol
# ........  ...............  ............................................... 
..........................................................
#
    93.93%         lto1-wpa  /usr/libexec/gcc/x86_64-pc-linux-gnu/4.7.0/lto1 
0x74a633         d [.] htab_expand
                   |
                   --- htab_expand

     1.05%          swapper  [kernel.kallsyms]                               
0xffffffff810460c2 k [k] default_idle
...

and sometimes (much more infrequent) this profile:

    40.25%         lto1-wpa  /usr/libexec/gcc/x86_64-pc-linux-gnu/4.7.0/lto1 
0x74ad05         d [.] htab_find_slot_with_hash
                   |
                   --- htab_find_slot_with_hash

    30.74%         lto1-wpa  /usr/libexec/gcc/x86_64-pc-linux-gnu/4.7.0/lto1 
0x225b10         d [.] eq_string_slot_node
                   |
                   --- eq_string_slot_node

     2.06%         lto1-wpa  /lib/libz.so.1.2.5   
...