[Bug middle-end/52066] New: IRA and reginfo initialization too expensive

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52066

             Bug #: 52066
           Summary: IRA and reginfo initialization too expensive
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: ja...@gcc.gnu.org


On compilation of an empty file, we spend almost half of the runtime on
IRA and reginfo cost initialization.

Inlining reg_class_subset_p and reg_classes_intersect_p gives us at least tiny
part of compile time back, at the cost of some small code growth.
For --enable-checking=release x86_64-linux cc1:

~/timing --drop 20 -c 2500 ./cc1.vanilla empty.c -quiet
Strip out best and worst 500 realtime results
minimum: 0.006243475 sec real / 0.000018634 sec CPU
maximum: 0.032220578 sec real / 0.000203440 sec CPU
average: 0.006542800 sec real / 0.000036352 sec CPU
stdev  : 0.000050402 sec real / 0.000004406 sec CPU
~/timing --drop 20 -c 2500 ./cc1 empty.c -quiet
Strip out best and worst 500 realtime results
minimum: 0.006115241 sec real / 0.000017569 sec CPU
maximum: 0.033226603 sec real / 0.000197238 sec CPU
average: 0.006384943 sec real / 0.000036349 sec CPU
stdev  : 0.000049180 sec real / 0.000004284 sec CPU

readelf -WS cc1{.vanilla,} | grep '\text'
  [12] .text             PROGBITS        00000000004b21a0 0b21a0 78e7b4 00  AX 
0   0 16
  [12] .text             PROGBITS        00000000004b21a0 0b21a0 78ed34 00  AX 
0   0 16