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Date: Thu, 3 Jul 2014 19:25:01 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
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Sender: Al Viro <viro@ftp.linux.org.uk>
Subject: Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions
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To: Richard Henderson <rth@twiddle.net>
Cc: Peter Maydell <peter.maydell@linaro.org>, QEMU Developers <qemu-devel@nongnu.org>

On Thu, Jul 03, 2014 at 07:51:04AM +0100, Al Viro wrote:

> FWIW, why not just generate
> 	trunc_i64_i32 tmp, va
> 	trunc_i64_i32 tmp2, vb
> 	muls2_i32 tmp2, tmp, tmp, tmp2
> 	ext32s_i64 vc, tmp2
> 	maybe_overflow_32 tmp
> where maybe_overflow throws IOV unless tmp is 0 or -1?
> to suffice for mull/v.  mulq/v would be
> 	muls2_i64 vc, tmp, va, vb
> 	maybe_overflow_64 tmp
> addl/v:
> 	trunc_i64_i32 tmp, va
> 	trunc_i64_i32 tmp2, vb
> 	add2_i32 tmp2, tmp, tmp, zero, tmp2, zero
> 	ext32s_i64 vc, tmp2
> 	maybe_overflow_32 tmp
> etc.

Grr...  Wrong check, obviously - we want to check that tmp + MSB(tmp2) is 0.
Something like
	setcond_32	tmp2, tmp2, zero, TCG_COND_LT
	add_i32		tmp, tmp2, tmp
	call		helper_IOV_if_not_zero tmp
for 32bit ones and
	setcond_64	tmp2, vc, zero, TCG_COND_LT
	add_i64		tmp, tmp2, tmp
	call		helper_IOV_if_not_zero tmp
for 64bit ones, or would it be better just to pass both arguments to helper
and let it deal with the check?  I'm not familiar enough with TCG, sorry...