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Date: Mon, 11 Oct 2004 13:52:00 -0000
From: "kazu at cs dot umass dot edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20041011135226.17931.kazu@cs.umass.edu>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug rtl-optimization/17931] New: andl and testb are not combined
X-Bugzilla-Reason: CC
X-SW-Source: 2004-10/txt/msg01400.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

Consider:

struct flags {
  unsigned f0 : 1;
  unsigned f1 : 1;
};

_Bool
foo (struct flags *p)
{
  if (p->f0)
    return 1;

  return p->f1;
}

With "cc1 -O2 -fomit-frame-pointer", I get

foo:
	movl	4(%esp), %eax
	movb	(%eax), %dl
	movb	%dl, %al
	andl	$1, %eax
	testb	%al, %al
	jne	.L7
	xorl	%eax, %eax
	testb	$2, %dl
	setne	%al
	ret
	.p2align 2,,3
.L7:
	movl	$1, %eax
	ret

Note that andl and testb are not combined to "testb $1, %al".
If they were combined, we would not destroy %eax,
so we would not need to make a copy of %al for a later use.

With -march=pentium4 or -march=athlon-xp, I get a similar result.

-- 
           Summary: andl and testb are not combined
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17931