[PATCH] Allocate constant size dynamic stack space in the prologue

[Jeff Law]

On 11/27/2015 07:09 AM, Dominik Vogt wrote:
> New patch with the following changes:
>
> * Fixed comment about dynamic var area placement.
> * The area is now placed further away from the stack pointer than
>    the non-dynamic stack variables (tested only with
>    STACK_GROWS_DOWNWARD).  This is a possible performance
>    improvement on S/390 (hoping that more variables will be
>    addressable using a displacement).
> * Moved the code that calculates the size to actually allocate
>    from the size required by dynamic stack variables to a separate
>    function.  Use that function from allocate_dynamic_stack_space()
>    and expand_stack_vars() so the size calculations are the same
>    for both.
> * Use a target hook to activate the feature (for now).
>    (This is just meant to make it more feasible to be included in
>    Gcc6.  If it's to late for this the code may be as well be used
>    for all targets.)
My inclination is for this to wait until gcc7.

jeff