[Bug rtl-optimization/21223] New: Output register variable is reloaded into the wrong register for asm

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

Compile this test with an ARM-targeted compiler.  Using -O2, it works out OK;
but for -O0 or -O1 it doesn't.  I originally encountered the bug in -O2 compiled
code, but a more complex testcase is probably necessary for that.

int bar(int *mem)
{
  return ({ register int a_oldval asm ("r0");
            register int a_tmp asm ("r3");
            int a_oldval2 = 3;
            __asm__ __volatile__ ("# Should be r0 - %0\n\t"
                                  "# Should be r3 - %1"
                                  : "=&r" (a_oldval), "=&r" (a_tmp)
                                  : "r" (a_oldval2));
            a_tmp; });
}

Everything is OK up until reload.  Then this happens:

Spilling for insn 19.
Using reg 2 for reload 0
Spilling for insn 19.
Using reg 2 for reload 0

Reloads for insn # 19
Reload 0: reload_out (SI) = (reg/v:SI 3 r3 [ a_tmp ])
        GENERAL_REGS, RELOAD_OTHER (opnum = 1)
        reload_out_reg: (reg/v:SI 3 r3 [ a_tmp ])
        reload_reg_rtx: (reg:SI 2 r2)

and the set of a_tmp is replaced by a set of r2.  I can't figure out why
the reload was created.

-- 
           Summary: Output register variable is reloaded into the wrong
                    register for asm
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: drow at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: arm-none-linux-gnueabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21223