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Date: Wed, 29 Sep 2004 17:58:00 -0000
From: "tromey at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20040929175802.17731.tromey@gcc.gnu.org>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug java/17731] New: sub-optimal code generated for left shift
X-Bugzilla-Reason: CC
X-SW-Source: 2004-09/txt/msg03670.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

Consider this java method:

  public int shift (int x, int y)
  {
    return x << y;
  }

On x86, with -O3, this becomes:

_ZN1t5shiftEii:
.LFB2:
	pushl	%ebp
.LCFI0:
	movl	%esp, %ebp
.LCFI1:
	movl	16(%ebp), %ecx
	movl	12(%ebp), %eax
	popl	%ebp
	andl	$31, %ecx
	sall	%cl, %eax
	ret


However, on x86 (starting with 80286), the shift count is masked
to 5 bits by sall, so the "andl" instruction is redundant.

I haven't looked to see exactly where this buglet might lie.

-- 
           Summary: sub-optimal code generated for left shift
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P2
         Component: java
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tromey at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org,java-prs at gcc dot gnu
                    dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17731