Preventing scheduling of normal operations across calls to built-ins

[Ian Lance Taylor]

Mohamed Shafi <shafitvm@gmail.com> writes:

> When you say UNSPEC_VOLATILE doesn't prevent instructions from moving,
> do you mean to say that such patterns will get reordered by the
> scheduler?

In general the instruction scheduler will not move instructions across
UNSPEC_VOLATILE instructions.  But the combiner will.  And the scheduler
implements scheduling barriers by inserting dependencies.  An
instruction which does not refer to registers or memory and is not
itself UNSPEC_VOLATILe does not have any dependencies, and I'm not sure
what the scheduler will do with it.

Ian