[Bug rtl-optimization/69847] Spec 2006 403.gcc slows down with -mlra vs. reload on PowerPC

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69847

--- Comment #8 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
(In reply to Michael Meissner from comment #7)
> The following options were used for LRA code generation:
> -DSPEC_CPU -DNDEBUG -I.  -g -mlittle -save-temps=obj -ffast-math -O3
> -mveclibabi=mass -mcpu=power8 -mrecip=rsqrt -fpeel-loops -funroll-loops
> -ftree-vectorize -fvect-cost-model -msave-toc-indirect
> -fno-aggressive-loop-optimizations -mno-pointers-to-nested-functions -mlra 
> -m64 -I/opt/at8.0/include
> -I/opt/at8.0/lib/gcc/powerpc64le-linux-gnu/4.9.4/include -fgnu89-inline     
> -DSPEC_CPU_LP64 -DSPEC_CPU -DSPEC_CPU2006 -DINLINE=
> 
> The following options were used for reload code generation:
> -DSPEC_CPU -DNDEBUG -I.  -g -mlittle -save-temps=obj -ffast-math -O3
> -mveclibabi=mass -mcpu=power8 -mrecip=rsqrt -fpeel-loops -funroll-loops
> -ftree-vectorize -fvect-cost-model -msave-toc-indirect
> -fno-aggressive-loop-optimizations -mno-pointers-to-nested-functions  -m64
> -I/opt/at8.0/include
> -I/opt/at8.0/lib/gcc/powerpc64le-linux-gnu/4.9.4/include -fgnu89-inline     
> -DSPEC_CPU_LP64 -DSPEC_CPU -DSPEC_CPU2006 -DINLINE=

Mike, thanks for a good and detail report.  After spending some time on
comparison of code generated by reload and LRA, at least I found that LRA
generates unnecessary address reloads:

      Creating newreg=225, assigning class BASE_REGS to addr r225
          alt=0,overall=0,losers=0,rld_nregs=0
         Choosing alt 0 in insn 15:  (0) =Y  (1) r {*movdi_internal64}
   15: [r225:DI+low(unspec[`*.LANCHOR0',%2:DI] 47)]=r181:DI
      REG_DEAD r181:DI
      REG_DEAD %2:DI
    Inserting insn reload before:
  133: r225:DI=high(unspec[`*.LANCHOR0',%2:DI] 47)

After checking what reload pass do in this situation, I found that reload
transforms the memnory address into sum of hi and low in the insn through
*LEGITIMIZE_RELOAD_ADDRESS* before actual reloading.

LRA does not use LEGITIMIZE_RELOAD_ADDRESS at all as the macro frequently uses
push_reload which is not a part of LRA.

I'll think how to fix it better.  Probably it will need introduction analogous
macro for LRA.