[llvm] r262505 - Revert "[X86] Elide references to _chkstk for dynamic allocas"

Hans Wennborg via llvm-commits llvm-commits at lists.llvm.org
Fri Mar 25 14:30:42 PDT 2016

On Wed, Mar 2, 2016 at 3:14 PM, Hans Wennborg <hans at chromium.org> wrote:
> On Wed, Mar 2, 2016 at 11:21 AM, Reid Kleckner via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> Author: rnk
>> Date: Wed Mar  2 13:20:59 2016
>> New Revision: 262505
>> URL: http://llvm.org/viewvc/llvm-project?rev=262505&view=rev
>> Log:
>> Revert "[X86] Elide references to _chkstk for dynamic allocas"
>> This reverts commit r262370.
>> It turns out there is code out there that does sequences of allocas
>> greater than 4K: http://crbug.com/591404
>> The goal of this change was to improve the code size of inalloca call
>> sequences, but we got tangled up in the mess of dynamic allocas.
>> Instead, we should come back later with a separate MI pass that uses
>> dominance to optimize the full sequence. This should also be able to
>> remove the often unneeded stacksave/stackrestore pairs around the call.
> Do you want to file a bug blocking PR26299 so we don't lose track of this?

Filed PR27076. I'll try to work on this, but I expect I'll need some pointers.

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