Re: Patch to reduce stack sizes

[Jeff Law <law at redhat dot com>]

On 05/06/10 18:22, Bernd Schmidt wrote:
> I've noticed every now and then while working on optimizations that when
> code generation is only slightly changed, the size of the stack frame
> can vary by more than one would expect.  I decided to find out why, and
> found the problem in reload.
>
> In reload's main loop, we align the stack frame in every iteration, so
> something like the following sequence can happen:
>    spill a register to a new 4-byte stack slot
>    align the stack to 16 bytes
>    spill another 4-byte register
>    align the stack to 16 bytes again
> which ends up wasting huge amounts of stack space.
>
> The following patch fixes it; assign_stack_local now keeps track of
> unused areas in the stack frame and tries to use them first.  In many
> cases on i686, this can reduce stack frames by 16 bytes or sometimes
> more.  Testing on ARM also showed some improvement.
>
> Bootstrapped and regression tested on i686-linux, also bootstrapped on
> ia64-linux (as a !FRAME_GROWS_DOWNWARD target).  Ok?
>    
I couldn't absolutely convince myself that the !FRAME_GROWS_DOWNWARD 
case was correct, nor could I convince myself it was incorrect.  I'll 
trust that in the unlikely event something proves problematical that 
you'll take care of it promptly.

Approved,

Jeff