From: Uros Bizjak <ubizjak@gmail.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: PATCH: PR target/44588: Very inefficient 8bit mod/div
Date: Tue, 22 Jun 2010 18:28:00 -0000 [thread overview]
Message-ID: <1277229955.2613.1.camel@localhost> (raw)
In-Reply-To: <20100621193321.GA13780@intel.com>
On Mon, 2010-06-21 at 12:33 -0700, H.J. Lu wrote:
> Hi,
>
> This patch adds 8bit divmov pattern for x86. X86 8bit divide
> instructions return result in AX with
>
> AL <- Quotient
> AH <- Remainder
>
> This patch models it and properly extends quotient. Tested
> on Intel64 with -m64 and -m32. There are no regressions.
> OK for trunk?
>
> BTW, there is only one divb used in subreg_get_info in
> gcc compilers. The old code is
>
> movzbl mode_size(%r13), %edi
> movzbl mode_size(%r14), %esi
> xorl %edx, %edx
> movl %edi, %eax
> divw %si
> testw %dx, %dx
> jne .L1194
>
> The new one is
>
> movzbl mode_size(%r13), %edi
> movl %edi, %eax
> divb mode_size(%r14)
> movzbl %ah, %eax
> testb %al, %al
> jne .L1194
>
Hm, something is not combined correctly, I'd say "testb %ah, %ah" is
optimal in the second case.
Uros.
next prev parent reply other threads:[~2010-06-22 18:06 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-21 20:38 H.J. Lu
2010-06-22 17:08 ` H.J. Lu
2010-06-22 18:28 ` Uros Bizjak [this message]
2010-06-22 18:36 ` H.J. Lu
2010-06-22 19:12 ` Uros Bizjak
2010-06-22 20:08 ` H.J. Lu
2010-06-23 6:26 ` Uros Bizjak
2010-06-23 16:54 ` H.J. Lu
2010-06-23 18:37 ` Paolo Bonzini
2010-06-23 18:46 ` H.J. Lu
2010-06-23 19:00 ` Paolo Bonzini
2010-06-23 19:08 ` H.J. Lu
2010-06-23 19:53 ` Paolo Bonzini
2010-06-23 20:22 ` H.J. Lu
2010-06-23 20:22 ` Paolo Bonzini
2010-06-23 20:27 ` H.J. Lu
2010-06-23 21:50 ` H.J. Lu
2010-06-23 22:44 ` H.J. Lu
2010-06-24 0:05 ` Paolo Bonzini
2010-06-24 0:54 ` H.J. Lu
2010-06-24 3:47 ` Paolo Bonzini
2010-06-24 17:38 ` H.J. Lu
2010-06-24 17:58 ` Paolo Bonzini
2010-06-24 19:01 ` Uros Bizjak
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