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* [Bug rtl-optimization/21991] New: missed-optimization setcc boolean compare
@ 2005-06-09 22:32 kellivoss25 at yahoo dot de
  2005-06-10 21:08 ` [Bug rtl-optimization/21991] " pinskia at gcc dot gnu dot org
  0 siblings, 1 reply; 3+ messages in thread
From: kellivoss25 at yahoo dot de @ 2005-06-09 22:32 UTC (permalink / raw)
  To: gcc-bugs

/*
the following case produces suboptimal code:

everything compiled with -O3 only
*/

extern char testcase(int* d)
{
	int w23;
	w23  = d[2] < d[3];
	w23 &= d[3] < d[2];

	return w23;
}

/*
4.1.0 20050410 m68k-aout (cygwin host)

testcase:
	link.w %fp,#0
	move.l 8(%fp),%a0
	move.l 8(%a0),%a1
	move.l 12(%a0),%d1
	cmp.l %a1,%d1
	sgt %d0
	extb.l %d0
	neg.l %d0
	cmp.l %a1,%d1
	slt %d1
	extb.l %d1
	neg.l %d1
	and.l %d1,%d0
	extb.l %d0
	unlk %fp
	rts


notice that the same cmp.l is executed 2 times
the same happened on the 3.4.1 i386 cygwin build:

3.4.1 x86 cygwin
_testcase:
	pushl	%ebp
	movl	%esp, %ebp
	movl	8(%ebp), %eax
	popl	%ebp
	movl	12(%eax), %edx
	movl	8(%eax), %ecx
	xorl	%eax, %eax
	cmpl	%edx, %ecx
	setl	%al
	cmpl	%edx, %ecx
	setg	%dl
	movzbl	%dl, %edx
	andl	%edx, %eax
	ret

the x86 build for 4.1.0 optimized the 2. cmp away but...

4.1.0 20050410 cygwin
_testcase:
	pushl	%ebp
	movl	%esp, %ebp
	movl	8(%ebp), %eax
	movl	8(%eax), %edx
	movl	12(%eax), %eax
	cmpl	%eax, %edx
	setl	%cl
	setg	%al
	movzbl	%al, %eax
	andl	%ecx, %eax
	leave
	ret


if we add a second block to make it more complex it returns.
*/

extern char testcase2(int* d)
{
	int w23,w13;
	w23  = d[2] < d[3];
	w23 &= d[3] < d[2];

	w13  = d[1] < d[3];
	w13 &= d[3] < d[1];

	return w23|w13;
}

/*

4.1.0 20050410 cygwin
_testcase:
	pushl	%ebp
	movl	%esp, %ebp
	pushl	%ebx
	pushl	%ecx
	movl	8(%ebp), %eax
	movl	8(%eax), %edx
	movl	12(%eax), %ecx
	cmpl	%ecx, %edx		;1
	setl	%bl
	movl	4(%eax), %eax	;2
	cmpl	%eax, %ecx
	setg	-5(%ebp)
	cmpl	%ecx, %edx		;1
	setg	%dl
	andl	%ebx, %edx
	cmpl	%eax, %ecx		;2
	setl	%al
	andb	-5(%ebp), %al
	orl	%edx, %eax
	movsbl	%al,%eax
	popl	%edx
	popl	%ebx
	leave
	ret


note: if in these redued function we replace the 
w23 &= d[3] < d[2];
with 
w23 = w23 && (d[3] < d[2])

we get the "correct"

return false;

but in my more complex project these double compares still 
show up even with &&;
*/

-- 
           Summary: missed-optimization setcc boolean compare
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kellivoss25 at yahoo dot de
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21991


^ permalink raw reply	[flat|nested] 3+ messages in thread
[parent not found: <bug-21991-4@http.gcc.gnu.org/bugzilla/>]
end of thread, other threads:[~2012-01-05 22:48 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2005-06-09 22:32 [Bug rtl-optimization/21991] New: missed-optimization setcc boolean compare kellivoss25 at yahoo dot de
2005-06-10 21:08 ` [Bug rtl-optimization/21991] " pinskia at gcc dot gnu dot org
     [not found] <bug-21991-4@http.gcc.gnu.org/bugzilla/>
2012-01-05 22:48 ` pinskia at gcc dot gnu.org

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