[Bug rtl-optimization/81625] GCC v4.7 ... v8 is bloating code by > 25% compared to v3.4

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81625

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Numbers for i586:

rguenther@murzim:/tmp> /space/rguenther/install/gcc-3.4.6/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
t.c:0: warning: `t.gcda' is version `408*', expected version `304*'
   text    data     bss     dec     hex filename
    855       0       0     855     357 t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.0.4/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
t.c:1: warning: ‘t.gcda’ is version ‘408*’, expected version ‘400*’
   text    data     bss     dec     hex filename
    860       0       0     860     35c t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.1.2/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
t.c:1: warning: ‘t.gcda’ is version ‘408*’, expected version ‘401*’
   text    data     bss     dec     hex filename
    874       0       0     874     36a t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.2.4/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
t.c:1: warning: 't.gcda' is version '408*', expected version '402*'
   text    data     bss     dec     hex filename
    855       0       0     855     357 t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.3.6/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
t.c:1: warning: 't.gcda' is version '408*', expected version '403*'
   text    data     bss     dec     hex filename
    894       0       0     894     37e t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.4.7/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
   text    data     bss     dec     hex filename
    889       0       0     889     379 t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.5.4/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
   text    data     bss     dec     hex filename
    893       0       0     893     37d t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.6.4/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
   text    data     bss     dec     hex filename
   1118       0       0    1118     45e t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.7.2/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
   text    data     bss     dec     hex filename
   1010       0       0    1010     3f2 t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.9.2/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
   text    data     bss     dec     hex filename
   1007       0       0    1007     3ef t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-5.2/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
   text    data     bss     dec     hex filename
    998       0       0     998     3e6 t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-6.4/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
   text    data     bss     dec     hex filename
    998       0       0     998     3e6 t.o
rguenther@murzim:/tmp> /space/rguenther/install/gcc-7.1/bin/gcc -c t.c -Os
-ffunction-sections -m32 -Wa,-32; size t.o
   text    data     bss     dec     hex filename
    999       0       0     999     3e7 t.o

so there's slow creep but the most significant regressions occured from
4.5 to 4.6 with 4.7 improving significantly again, afterwards the creep
stopped at least.

i586 and not x86_64 because I lack historical 64bit compilers.

Note I had to short-circuit the asm in snake_random_pixel, I'm just using
an external function for x86.

The above is probably not too useful and also architecture specific.  There
isn't anything obviously wrong happening on the GIMPLE level.