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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/52628] New: SH Target: Inefficient shift by T bit result
Date: Mon, 19 Mar 2012 23:42:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52628

             Bug #: 52628
           Summary: SH Target: Inefficient shift by T bit result
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: olegendo@gcc.gnu.org
            Target: sh*-*-*


int test_01 (int a, int b, int c)
{
  return c << (a > b ? 1 : 0);
}

-m4 -O2:
        cmp/gt    r5,r4
        mov    r6,r0
        movt    r1
        rts    
        shld    r1,r0

better:
        cmp/gt    r5,r4
        bf    0f
        add     r6,r6     ! do not use shll because of T bit usage in shll
0:
        rts
        mov    r6,r0



int test_02 (int a, int b, int c)
{
  return c << (a > b ? 2 : 0);
}

-m4 -O2:
        cmp/gt    r5,r4
        mov    r6,r0
        movt    r1
        add    r1,r1
        rts    
        shld    r1,r0

better:
        cmp/gt    r5,r4
        bf    0f
        shll2    r6
0:
        rts
        mov    r6,r0


The same goes for other shift amounts like 8 and 16.
On SH4 the zero-displacement conditional branch code should be faster.