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Re: [Qemu-devel] [PATCH 13/14] i386: optimize setbe
From: |
Richard Henderson |
Subject: |
Re: [Qemu-devel] [PATCH 13/14] i386: optimize setbe |
Date: |
Tue, 09 Oct 2012 13:13:11 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 |
On 10/06/2012 05:30 AM, Paolo Bonzini wrote:
> gen_compute_eflags(s);
> - tcg_gen_shri_tl(reg, cpu_cc_src, 6);
> - tcg_gen_or_tl(reg, reg, cpu_cc_src);
> - tcg_gen_andi_tl(reg, reg, 1);
> - break;
> + tcg_gen_andi_tl(reg, cpu_cc_src, 0x41);
> + tcg_gen_setcondi_tl(inv ? TCG_COND_EQ : TCG_COND_NE, reg, reg, 0);
> + return;
This one's questionable. Whether it's an improvement really depends
on the host cpu isa. It's probably more of a benefit if we can avoid
the setcond completely. See the comments for the next patch.
That said, the patch produces correct code.
Reviewed-by: Richard Henderson <address@hidden>
r~
- [Qemu-devel] [PATCH 08/14] i386: do not compute eflags multiple times consecutively, (continued)
- [Qemu-devel] [PATCH 08/14] i386: do not compute eflags multiple times consecutively, Paolo Bonzini, 2012/10/06
- [Qemu-devel] [PATCH 05/14] i386: move eflags computation closer to gen_op_set_cc_op, Paolo Bonzini, 2012/10/06
- [Qemu-devel] [PATCH 10/14] i386: use inverted setcond when computing NS or NZ, Paolo Bonzini, 2012/10/06
- [Qemu-devel] [PATCH 13/14] i386: optimize setbe, Paolo Bonzini, 2012/10/06
- [Qemu-devel] [PATCH 12/14] i386: change gen_setcc_slow_T0 to gen_setcc_slow, Paolo Bonzini, 2012/10/06
- [Qemu-devel] [PATCH 11/14] i386: convert gen_compute_eflags_c to TCG, Paolo Bonzini, 2012/10/06
- [Qemu-devel] [PATCH 14/14] i386: optimize setcc instructions, Paolo Bonzini, 2012/10/06