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From: Richard Henderson <rth@twiddle.net>
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Date: Fri, 17 Jul 2015 07:38:03 +0100
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Subject: Re: [Qemu-devel] [PATCH RFC 8/9] tcg/optimize: do not simplify size
	changing moves
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To: Aurelien Jarno <aurelien@aurel32.net>, qemu-devel@nongnu.org
Cc: Paolo Bonzini <pbonzini@redhat.com>

On 07/15/2015 12:03 PM, Aurelien Jarno wrote:
> Now that we have real size changing ops, we don't need to marked high
> bits of the destination as garbage. The goal of the optimizer is to
> predict the value of the temps (and not of the registers) and do
> simplifications when possible. The problem there is therefore not the
> fact that those bits are not counted as garbage, but that a size
> changing op is replaced by a move.
>
> This patch is basically a revert of 24666baf, including the changes that
> have been made since then.
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

What we're missing here is whether the omitted size changing op is extu or 
exts.  Mask should be extended to match.  Which means keeping most of this code.


r~