libgcc: strange optimization

[Richard Henderson]

On 08/02/2011 05:22 AM, Richard Guenther wrote:
>> -fno-tree-ter also unbreaks the ARM test case in PR48863 comment #4.
> 
> It's of course only a workaround, not a real fix as nothing prevents
> other optimizers from performing the re-scheduling TER does.
> 
> I suggest to amend the documentation for local call-clobbered register
> variables to say that the only valid sequence using them is from a
> non-inlinable function that contains only direct initializations of the
> register variables from constants or parameters.
> 
> Or go one step further and deprecate local register variables alltogether
> (they IMHO don't make much sense, and rather the targets should provide
> a way to properly constrain asm inputs and outputs).

Neither of these is a viable option.

What we might be able to do is throttle TER when the destination
is a local register variable.  This should unbreak the common case
of local regs immediately surrounding an asm.


r~