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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