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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/61142] New: [SH] QImode/HImode @(R0,Rm),Rn does not load to Rn = R0
Date: Sat, 10 May 2014 21:27:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61142

            Bug ID: 61142
           Summary: [SH] QImode/HImode @(R0,Rm),Rn does not load to Rn =
                    R0
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org
            Target: sh*-*-*

I've noticed that @(R0,Rm),Rn loads won't load into Rn = R0.
Example:

int test0 (const char* x, int a, int b, int c)
{
  if (x[a] == 92)
    return b;
  return c;
}

With -O2 -m4 -ml compiles to:
        mov     r5,r0
        mov.b   @(r0,r4),r1  <<<<
        mov     r1,r0        <<<<
        cmp/eq  #92,r0
        bt      .L3
        mov     r7,r0
        rts
        nop
    .align 1
.L3:
        rts
        mov     r6,r0

This happens for QImode and HImode loads.  SImode is fine.

I'm not sure whether it's a side effect of the changes done for PR 50751, or
something else.

It could be worked around with a peephole, but then we'd waste one register.