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Subject: [Bug target/49263] SH Target: underutilized "TST #imm, R0" instruction
Date: Sun, 20 Nov 2011 14:20:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49263

--- Comment #14 from Oleg Endo <oleg.endo@t-online.de> 2011-11-20 13:04:39 UTC ---
With trunk rev 181517 I have observed the following problem, which happens when
compiling for -m2*, -m3*, -m4* and -Os:

The function compiled with -m2 -Os

int test_int64_lowword (long long* x)
{
  return *x & 0xFFFFFFFF ? -20 : -40;
}

results in the following code:

    mov    #0,r2    ! 42    movsi_i/3    [length = 2]
    tst    r2,r2    ! 44    cmpeqsi_t/1    [length = 2]
    bf.s    .L4    ! 45    branch_false    [length = 2]
    mov.l    @(4,r4),r3    ! 12    movsi_i/5    [length = 2]
    tst    r3,r3    ! 46    cmpeqsi_t/1    [length = 2]
.L4:
    bt    .L3    ! 14    branch_true    [length = 2]
    mov    #-20,r0    ! 4    movsi_i/3    [length = 2]
    rts    
    nop    ! 52    *return_i    [length = 4]
.L3:
    rts        ! 54    *return_i    [length = 2]
    mov    #-40,r0    ! 5    movsi_i/3    [length = 2]

When compiled with -O1 or -O2 the high word test is completely eliminated
correctly:

    mov.l    @(4,r4),r1    ! 10    movsi_i/5    [length = 2]
    tst    r1,r1    ! 17    cmpeqsi_t/1    [length = 2]
    bt    .L4    ! 18    branch_true    [length = 2]
    mov    #-20,r0    ! 4    movsi_i/3    [length = 2]
    rts    
    nop    ! 50    *return_i    [length = 4]
.L4:
    rts        ! 52    *return_i    [length = 2]
    mov    #-40,r0    ! 5    movsi_i/3    [length = 2]

I'm not sure whether this is actually related to this PR, but have noticed it
with the test cases of this PR.  It seems only to happen for comparison-like
insns.  If I remember correctly, this problem did not exist when I started
working on this PR.