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Re: [Qemu-arm] [Qemu-devel] [PATCH v2 66/68] target/arm: Convert T16, lo


From: Aleksandar Markovic
Subject: Re: [Qemu-arm] [Qemu-devel] [PATCH v2 66/68] target/arm: Convert T16, long branches
Date: Tue, 3 Sep 2019 11:40:45 +0200


28.08.2019. 02.07, "Richard Henderson" <address@hidden> је написао/ла:
>
> On 8/27/19 2:34 AM, Peter Maydell wrote:
> >> +    tcg_gen_andi_i32(tmp, tmp, -4);
> >
> > Minor nit, but can we use 0xfffffffc like the old code did,
> > to avoid the reader having to do 2s-complement arithmetic
> > in their head to figure out that we're clearing the low 2 bits?
>
> I always preferred "x & -c" for exactly the same reason:
> to avoid the reader having to do 2s compliment arithmetic
> in their head to figure out that we're aligning to c.
>
> But, sure, if you like.
>

I vote for 0xfffffffc.

Aleksandar

> > This would be a good place to put a comment equivalent to that
> > in the old decoder:
> >
> > # thumb_insn_is_16bit() ensures we won't be decoding these as
> > # T16 instructions for a Thumb2 CPU, so these patterns must be
> > # a Thumb1 split BL/BLX.
> >
> >> +BLX_suffix      11101 imm:11                    &i
> >> +BL_BLX_prefix   11110 imm:s11                   &i
> >> +BL_suffix       11111 imm:11                    &i
>
> I had placed that with trans_BL_BLX_prefix, but I suppose this
> is a better place.
>
>
> r~
>


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