From: Richard Henderson <rth@twiddle.net>
To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org, agraf@suse.de
Subject: Re: [Qemu-devel] [PATCH 08/12] tcg-s390: Remove constraint letters for and
Date: Thu, 28 Mar 2013 08:08:23 -0700 [thread overview]
Message-ID: <51545CE7.30402@twiddle.net> (raw)
In-Reply-To: <20130328150327.GC5000@ohm.aurel32.net>
On 03/28/2013 08:03 AM, Aurelien Jarno wrote:
>> Since we have a free temporary and can always just load the constant, we
>> > ought to do so, rather than spending the same effort constraining the const.
> Is it really a good idea doing so? If a constraint can't be satisfied
> the TCG code will also load the constant in a register, with the
> difference that the register is not trashed and might be reused later
> instead of reloading the constant again. Of course it means one more
> register available, but the S390 target doesn't really have issues
> with the number of available registers.
>
My main thinking is along the lines you yourself pointed out when the code
was first written -- it's really quite hard to figure out what constants are
implementable for AND.
It gets even worse with a patch further in the series that uses ROTATE AND
INSERT SELECTED BITS.
It's complicated enough that it *seems* better to just go ahead and accept
all constants. Even from a maintainence point of view -- we no longer have
to have two big functions match up.
r~
next prev parent reply other threads:[~2013-03-28 15:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-27 18:52 [Qemu-devel] [PATCH 00/12] tcg-s390 updates Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 01/12] tcg-s390: Fix movi Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 02/12] tcg-s390: Properly allocate a stack frame Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 03/12] tcg-s390: Remove useless preprocessor conditions Richard Henderson
2013-03-28 0:14 ` Aurelien Jarno
2013-03-28 0:54 ` Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 04/12] tcg-s390: Implement add2/sub2 opcodes Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 05/12] tcg-s390: Implement mulu2_i64 opcode Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 06/12] tcg-s390: Implement movcond opcodes Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 07/12] tcg-s390: Implement deposit opcodes Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 08/12] tcg-s390: Remove constraint letters for and Richard Henderson
2013-03-28 15:03 ` Aurelien Jarno
2013-03-28 15:08 ` Richard Henderson [this message]
2013-03-27 18:52 ` [Qemu-devel] [PATCH 09/12] tcg-s390: Use risbgz for andi Richard Henderson
2013-03-27 19:03 ` Paolo Bonzini
2013-03-27 19:27 ` Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 10/12] tcg-s390: Cleanup argument shuffling fixme in softmmu code Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 11/12] tcg-s390: Use load-address for addition Richard Henderson
2013-03-27 18:52 ` [Qemu-devel] [PATCH 12/12] tcg-s390: Use all 20 bits of the offset in tcg_out_mem Richard Henderson
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