[Bug target/54830] [SH] Unnecessary exts.w before extu.b

[olegendo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54830

--- Comment #1 from Oleg Endo <olegendo at gcc dot gnu.org> 2012-10-18 19:24:36 UTC ---
Created attachment 28487
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28487
Reduced test case

This is the reduced test case.  It shows that there are actually two redundant
zero/sign extensions when compiling with -m4 {-ml|-mb} -O2:

   swap.w       r5,r5   ! 88    rotlsi3_16
   ...
   exts.w       r5,r5   ! 89    *extendhisi2_compact_reg
   ...
   extu.b       r5,r9   ! 10    *zero_extendqisi2_compact
   ...
   extu.b       r9,r12  ! 11    *zero_extendqisi2_compact
   ...

Turning on the REE pass (-free) doesn't seem to help this either.
Adding the following pattern to sh.md:

(define_insn_and_split "*"
  [(set (match_operand:SI 0 "register_operand")
    (zero_extract:SI (match_operand:SI 1 "register_operand")
             (const_int 8)
             (const_int 16)))]
  "TARGET_SH1"
  "#"
  "&& 1"
  [(set (match_dup 0) (lshiftrt:SI (match_dup 1) (const_int 16)))
   (set (match_dup 0) (zero_extend:SI (match_dup 2)))]
{
  operands[2] = gen_lowpart (QImode, operands[0]);
})


eliminates the first sign-extension (exts.w) only.  The second zero-extension
can be eliminated by extending sh_try_omit_signzero_extend in sh.c accordingly.