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From: "kyukhin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/66665] New: Increment instruction is not propagated into address operand
Date: Thu, 25 Jun 2015 13:06:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66665

            Bug ID: 66665
           Summary: Increment instruction is not propagated into address
                    operand
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kyukhin at gcc dot gnu.org
  Target Milestone: ---

Hello,

Running this:
make check-gcc RUNTESTFLAGS="CFLAGS='-mregparm=3'
--target_board='unix/-mregparm=3{-m32}' i386.exp=addr-sel-1.c"

If got fail since:
f:
.LFB0:
        movsbl  a+1(%eax), %edx
        incl    %eax            ;; Not propagated ...
        movsbl  b(%eax), %eax   ;; ... to here.
        addl    %edx, %eax
        ret

Increment of %eax is not propagated into load of b.

This kind of propagation is occurred during postreload in `reload_cse_regs',
but increment is promoted to load of a.