On 2017-12-17 22:21, Hauke Mehrtens wrote:
> This patch made GCC produce broken code, remove it.
> In mp_cmp_d() function in th libtommath shipped with dropbear the
> following code was compiled wrong:
>
> /* compare based on magnitude */
> if (a->used > 1) {
> return 1;
> }
>
> In the broken ASM this part returned -1 like the previous return
> statement did instead of 1 like it should.
>
> This did not happen when the -funroll-loops option was given to GCC.
>
> Signed-off-by: Hauke Mehrtens <ha...@hauke-m.de>
This patch only passes the cost associated with branches and memory
transfers to other parts of GCC, which causes it to generate different
code (matching what it already does on -O2).
I'm pretty sure that by removing the patch you're simply hiding the real
issue which can easily creep in again in other places when compiling
with -O2. I don't think we can trust GCC 7 on MIPS before we find and
fix the real bug.
- Felix
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