[PATCH 1/2][v3] Drop excess size used for run time allocated stack variables.

[Dominik Vogt]

On Tue, May 03, 2016 at 03:17:53PM +0100, Dominik Vogt wrote:
> Version two of the patch including a test case.
> 
> On Mon, May 02, 2016 at 09:10:25AM -0600, Jeff Law wrote:
> > On 04/29/2016 04:12 PM, Dominik Vogt wrote:
> > >The attached patch removes excess stack space allocation with
> > >alloca in some situations.  Plese check the commit message in the
> > >patch for details.
> 
> > However, I would strongly recommend some tests, even if they are
> > target specific.  You can always copy pr36728-1 into the s390x
> > directory and look at size of the generated stack.  Simliarly for
> > pr50938 for x86.
> 
> However, x86 uses the "else" branch in round_push, i.e. it uses
> "virtual_preferred_stack_boundary_rtx" to calculate the number of
> bytes to add for stack alignment.  That value is unknown at the
> time round_push is called, so the test case fails on such targets,
> and I've no idea how to fix this properly.

Third version of the patch with the suggested cleanup in the first
patch and the functional stuff in the second one.  The first patch
is based on Jeff's draft with the change suggested by Eric and
more cleanup added by me.

Tested and bootstrapped on s390x biarch (but did not look for
performance regressions as the change should be a no-op).

Ciao

Dominik ^_^  ^_^

-- 

Dominik Vogt
IBM Germany
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gcc/ChangeLog0

	* explow.c (allocate_dynamic_stack_space): Simplify knowing that
	MUST_ALIGN was always true and extra_align ist always BITS_PER_UNIT.
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