From: Richard Henderson <rth@twiddle.net>
To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 2/7] tcg: Optimize add2 + sub2
Date: Thu, 27 Sep 2012 16:28:47 -0700 [thread overview]
Message-ID: <5064E12F.5040308@twiddle.net> (raw)
In-Reply-To: <20120927232015.GN23819@ohm.aurel32.net>
On 09/27/2012 04:20 PM, Aurelien Jarno wrote:
> I understand that we can't easily insert an instruction, so the
> limitation comes from here, but is it really something happening often?
It will certainly appear sometimes. E.g. s390x has an add immediate
instruction that does exactly: r1 += imm16 << 32.
Or did you mean specifically the full constant being folded? That
would happen quite a bit more often. That you can see with most any
64-bit RISC guest when they attempt to generate a constant from
addition primitives instead of logical primitives.
For a 32-bit host, we've already decomposed logical primitives to 32-bit
operations. And we can constant-fold through all of those. But when
addition comes into play, we can't constant-fold through add2.
r~
next prev parent reply other threads:[~2012-09-27 23:28 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-27 17:19 [Qemu-devel] [PATCH 0/7] Double-word tcg/optimize improvements Richard Henderson
2012-09-27 17:19 ` [Qemu-devel] [PATCH 1/7] tcg: Split out swap_commutative as a subroutine Richard Henderson
2012-09-27 21:45 ` Aurelien Jarno
2012-09-27 17:19 ` [Qemu-devel] [PATCH 2/7] tcg: Optimize add2 + sub2 Richard Henderson
2012-09-27 23:20 ` Aurelien Jarno
2012-09-27 23:28 ` Richard Henderson [this message]
2012-10-01 17:46 ` Aurelien Jarno
2012-10-01 18:41 ` Richard Henderson
2012-09-30 7:04 ` Blue Swirl
2012-10-01 18:36 ` Richard Henderson
2012-09-27 17:19 ` [Qemu-devel] [PATCH 3/7] tcg: Swap commutative double-word comparisons Richard Henderson
2012-09-27 23:22 ` Aurelien Jarno
2012-09-27 17:19 ` [Qemu-devel] [PATCH 4/7] tcg: Optimize double-word comparisons against zero Richard Henderson
2012-10-01 18:43 ` Aurelien Jarno
2012-10-01 18:47 ` Richard Henderson
2012-09-27 17:19 ` [Qemu-devel] [PATCH 5/7] tcg: Split out subroutines from do_constant_folding_cond Richard Henderson
2012-10-01 18:46 ` Aurelien Jarno
2012-09-27 17:19 ` [Qemu-devel] [PATCH 6/7] tcg: Tidy brcond optimization Richard Henderson
2012-10-01 18:48 ` Aurelien Jarno
2012-09-27 17:19 ` [Qemu-devel] [PATCH 7/7] tcg: Do constant folding on double-word comparisons Richard Henderson
2012-10-01 18:50 ` Aurelien Jarno
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