Le 11/02/2021 à 15:30, Segher Boessenkool a écrit :
On Thu, Feb 11, 2021 at 03:09:43PM +0100, Christophe Leroy wrote:
Le 11/02/2021 à 12:49, Segher Boessenkool a écrit :
On Thu, Feb 11, 2021 at 07:41:52AM +, Christophe Leroy wrote:
powerpc BUG_ON() is based on using twnei or tdnei instr
Excerpts from Segher Boessenkool's message of February 11, 2021 9:50 pm:
> On Thu, Feb 11, 2021 at 08:04:55PM +1000, Nicholas Piggin wrote:
>> It would be nice if we could have a __builtin_trap_if that gcc would use
>> conditional traps with, (and which never assumes following code is
>> unreacha
Le 11/02/2021 à 15:30, Segher Boessenkool a écrit :
On Thu, Feb 11, 2021 at 03:09:43PM +0100, Christophe Leroy wrote:
Le 11/02/2021 à 12:49, Segher Boessenkool a écrit :
On Thu, Feb 11, 2021 at 07:41:52AM +, Christophe Leroy wrote:
powerpc BUG_ON() is based on using twnei or tdnei instr
On Thu, Feb 11, 2021 at 03:09:43PM +0100, Christophe Leroy wrote:
> Le 11/02/2021 à 12:49, Segher Boessenkool a écrit :
> >On Thu, Feb 11, 2021 at 07:41:52AM +, Christophe Leroy wrote:
> >>powerpc BUG_ON() is based on using twnei or tdnei instruction,
> >>which obliges gcc to format the conditi
Le 11/02/2021 à 12:49, Segher Boessenkool a écrit :
On Thu, Feb 11, 2021 at 07:41:52AM +, Christophe Leroy wrote:
powerpc BUG_ON() is based on using twnei or tdnei instruction,
which obliges gcc to format the condition into a 0 or 1 value
in a register.
Huh? Why is that?
Will it work
On Thu, Feb 11, 2021 at 01:26:12PM +0100, Christophe Leroy wrote:
> >What PowerPC cpus implement branch folding? I know none.
>
> Extract from powerpc mpc8323 reference manual:
> — Zero-cycle branch capability (branch folding)
Yeah, this is not what is traditionally called branch folding (which
Le 11/02/2021 à 12:49, Segher Boessenkool a écrit :
On Thu, Feb 11, 2021 at 07:41:52AM +, Christophe Leroy wrote:
powerpc BUG_ON() is based on using twnei or tdnei instruction,
which obliges gcc to format the condition into a 0 or 1 value
in a register.
Huh? Why is that?
Will it work
On Thu, Feb 11, 2021 at 08:04:55PM +1000, Nicholas Piggin wrote:
> Excerpts from Christophe Leroy's message of February 11, 2021 5:41 pm:
> > As modern powerpc implement branch folding, that's even more efficient.
Ah, it seems you mean what Arm calls branch folding. Sure, power4
already did that,
On Thu, Feb 11, 2021 at 08:04:55PM +1000, Nicholas Piggin wrote:
> It would be nice if we could have a __builtin_trap_if that gcc would use
> conditional traps with, (and which never assumes following code is
> unreachable even for constant true, so we can use it with WARN and put
> explicit unr
On Thu, Feb 11, 2021 at 07:41:52AM +, Christophe Leroy wrote:
> powerpc BUG_ON() is based on using twnei or tdnei instruction,
> which obliges gcc to format the condition into a 0 or 1 value
> in a register.
Huh? Why is that?
Will it work better if this used __builtin_trap? Or does the kern
Excerpts from Christophe Leroy's message of February 11, 2021 5:41 pm:
> powerpc BUG_ON() is based on using twnei or tdnei instruction,
> which obliges gcc to format the condition into a 0 or 1 value
> in a register.
>
> By using a generic implementation, gcc will generate a branch
> to the uncond
powerpc BUG_ON() is based on using twnei or tdnei instruction,
which obliges gcc to format the condition into a 0 or 1 value
in a register.
By using a generic implementation, gcc will generate a branch
to the unconditional trap generated by BUG().
As modern powerpc implement branch folding, that'
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