[Bug rtl-optimization/31849] New: Code size regression caused by fix to PR 31360

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

The fix to PR31360 has caused significant code size regressions on ARM-EABI. 
An example of this is from zlib (adler32.c) and is attached, compile with -Os
-mcpu=arm7tdmi -fno-short-enums -w 

The new code:
1) Hoists a register containing 0 out of the loop
2) Uses that *only* as a copy into another register (mov reg, #0 costs exactly
the same as mov reg, reg)
3) By doing the above, somehow prevents the post-increment sequence from being
found.
4) Forces another register to be saved by the function.


-- 
           Summary: Code size regression caused by fix to PR 31360
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rearnsha at gcc dot gnu dot org
GCC target triplet: arm-none-eabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31849