Re: impact of -minsert-sched-nops

[Dorit Naishlos <DORIT at il dot ibm dot com>]

>    Well, as I understood it, the -minsert-sched-nops feature could be
> enabled through either -mcpu=970 or -mcpu=G5 or -mcpu=power4 (which
> would make the code G5 specific) or just through -minsert-sched-nops
> which would limit the change to that optimization leaving the code
> G4 compatible. Or am I missing something here?
>
This is not entirely accurate: -minsert-sched-nops will not have an effect
unless the machine description that the compiler uses is POWER4.
POWER4 is the machine description that describes the G5 machine.
If you want the compiler to use this machine description, you can specify
-mcpu=970 or -mcpu=G5 or -mcpu=power4.

PPC7450 is the machine description that describes the G4 machine.
The option -minsert-sched-nops=scheme does not have an effect when this
machine description is used, since it is not relevant for machine
descriptions other than POWER4.

>    From reading the patch, I thought the default was mode 2 which
> is for the power4?
>
If you specify -mcpu=970/G5/power4, then -minsert-sched-nops=scheme is
enabled by default with scheme="regroup_exact".
You can enable different schemes of this optimizations if you use
-mcpu=970/G5/power4 and -minsert-sched-nops=scheme, with different values
for scheme, as described here:
http://gcc.gnu.org/onlinedocs/gcc/RS-6000-and-PowerPC-Options.html.

dorit