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Subject: Re: [Qemu-devel] [PATCH v3 06/14] tcg: Allow non-constant control
 macros
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: aliguori@us.ibm.com, claudio.fontana@huawei.com, qemu-devel@nongnu.org, afaerber@suse.de

On 07/04/2013 03:53 AM, Peter Maydell wrote:
> On 3 July 2013 22:29, Richard Henderson <rth@twiddle.net> wrote:
>> This allows TCG_TARGET_HAS_* to be a variable rather than a constant,
>> which allows easier support for differing ISA levels for the host.
> 
> The effect of this is that TCG_OPF_NOT_PRESENT means "if set,
> op is definitely not present; if not set, op might or might
> not be present", right? Which is OK because it's just a debug
> guard/sanity check. (That might be worth noting in a comment
> I guess.)

Well, if not set, an entry must be present in the operands table.

E.g. for arm division, the { INDEX_op_div_i32, "r", "r", "r" } entry
is always there, even if TCG_TARGET_HAS_div_i32 evaluates to false
at runtime.  The entry must be there Just In Case the expression might
be true.


r~