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From: Peter Maydell <peter.maydell@linaro.org>
Date: Thu, 19 Dec 2013 21:23:38 +0000
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Subject: Re: [Qemu-devel] [PATCH 17/21] target-arm: A64: add support for
 conditional compare insns
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To: Richard Henderson <rth@twiddle.net>
Cc: Patch Tracking <patches@linaro.org>, Michael Matz <matz@suse.de>, QEMU Developers <qemu-devel@nongnu.org>, Claudio Fontana <claudio.fontana@linaro.org>, Dirk Mueller <dmueller@suse.de>, Will Newton <will.newton@linaro.org>, Laurent Desnogues <laurent.desnogues@gmail.com>, =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>, "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>, Christoffer Dall <christoffer.dall@linaro.org>

On 19 December 2013 21:04, Richard Henderson <rth@twiddle.net> wrote:
> On 12/17/2013 07:12 AM, Peter Maydell wrote:
>
>> +    tcg_tmp = tcg_temp_new_i64();
>> +
>> +    if (cond < 0x0e) { /* not always */
>> +        int label_match = gen_new_label();
>> +        label_continue = gen_new_label();
>> +        arm_gen_test_cc(cond, label_match);
>> +        /* nomatch: */
>> +        tcg_gen_movi_i64(tcg_tmp, nzcv << 28);
>> +        gen_set_nzcv(tcg_tmp);
>> +        tcg_gen_br(label_continue);
>> +        gen_set_label(label_match);
>> +    }
>
> You can't re-use tcg_tmp across basic blocks like this.

Hmm. I clearly don't entirely understand the rules here.
The TCG README says "temporaries are only live
in a basic block" and "After the end of a basic block, the
content of temporaries is destroyed", which I took to
mean that the value in the temp was dead after the
branch, but that I could freely reuse it for something
else afterwards as long as I wrote a new value to
it (as we're doing here). I guess that's wrong?

thanks
-- PMM