OK, thanks for your answer.
Is there other instruction for backward jumps that can be used
to replace cmp to zero+bne?
btw, in the following link of thumb-2 instructions set I understood that
the label can appear before the branch so it was confusing...
CB{N}Z Rn,<label> If Rn {== or !=} 0 then PC := label. label is (this
instruction + 4-130).
http://infocenter.arm.com/help/topic/com.arm.doc.qrc0001l/QRC0001_UAL.pdf
Thanks,
Revital
From: Chung-Lin Tang <clt...@codesourcery.com>
To: Revital1 Eres/Haifa/i...@ibmil
Cc: linaro-toolchain@lists.linaro.org
Date: 29/11/2010 10:21 AM
Subject: Re: A question about thumb2 cbnz/cbz implementation in
thumb2.md
Unfortunately, cbnz/cbz has a 6-bit:'0' (7-bit aligned to 2) immediate
offset that is *zero extended*, i.e. it is only for forward branches.
Chung-Lin
On 2010/11/29 下午 04:14, Revital1 Eres wrote:
>
> Hello,
>
> I have a question about cbnz/cbz thumb-2 instruction implementation in
> thumb2.md file:
>
> I have an example where we jump to a label which appears before the
branch;
> for example:
>
> L4
> ...
> cmp r3, 0
> bne .L4
>
> It seems that cbnz instruction should be applied in this loop; replacing
> cmp+bne; however, cbnz fails to be applied as diff = ADDRESS (L4) -
ADDRESS
> (bne .L4) is negative and according to thumb2_cbz in thumb2.md it should
> be 2<=diff<=128 (please see snippet below taken from thumb2_cbz).
>
> So I want to double check if the current implementation of thumb2_cbnz
> in thumb2.md needs to be changed to enable it.
>
> The following is from thumb2_cbnz in thumb2.md:
>
> [(set (attr "length")
> (if_then_else
> (and (ge (minus (match_dup 1) (pc)) (const_int 2))
> (le (minus (match_dup 1) (pc)) (const_int 128))
> (eq (symbol_ref ("which_alternative")) (const_int 0)))
> (const_int 2)
> (const_int 8)))]
>
> Thanks,
> Revital
>
>
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