Re: [google] pessimize stack accounting during inlining

[Richard Guenther <richard dot guenther at gmail dot com>]

On Fri, Jun 10, 2011 at 1:45 AM, Mark Heffernan <meheff@google.com> wrote:
> On Wed, Jun 8, 2011 at 1:54 AM, Richard Guenther
> <richard.guenther@gmail.com> wrote:
>> Well, it's still not a hard limit as we can't tell how many spill slots
>> or extra call argument or return value slots we need.
>
> Agreed. ?It's not perfect. ?But I've found this does a reasonable job
> of preventing the inliner from pushing the frame size much beyond the
> imposed limit especially if the limit is large (eg, many K) relative
> to the typical total size of spill slots, arguments, etc.

Do you have a testcase?

Richard.

> Mark
>
>>
>> Richard.
>>
>> > Thanks,
>> >
>> > David
>> >
>> > On Tue, Jun 7, 2011 at 4:29 PM, Mark Heffernan <meheff@google.com> wrote:
>> >> This patch pessimizes stack accounting during inlining. ?This enables
>> >> setting a firm?stack size limit (via parameters?"large-stack-frame" and
>> >> "large-stack-frame-growth"). ?Without this patch the inliner is overly
>> >> optimistic about potential stack reuse resulting in actual stack frames much
>> >> larger than the parameterized limits.
>> >> Internal benchmarks show minor performance differences with non-fdo and
>> >> lipo, but overall neutral. ?Tested/bootstrapped on x86-64.
>> >> Ok for google-main?
>> >> Mark
>> >>
>> >> 2011-06-07 ?Mark Heffernan ?<meheff@google.com>
>> >> ? ? ? ? * cgraph.h (cgraph_global_info): Remove field.
>> >> ? ? ? ? * ipa-inline.c (cgraph_clone_inlined_nodes): Change
>> >> ? ? ? ? stack frame computation.
>> >> ? ? ? ? (cgraph_check_inline_limits): Ditto.
>> >> ? ? ? ? (compute_inline_parameters): Remove dead initialization.
>> >>
>> >> Index: gcc/cgraph.h
>> >> ===================================================================
>> >> --- gcc/cgraph.h ? ? ? ?(revision 174512)
>> >> +++ gcc/cgraph.h ? ? ? ?(working copy)
>> >> @@ -136,8 +136,6 @@ struct GTY(()) cgraph_local_info {
>> >> ?struct GTY(()) cgraph_global_info {
>> >> ? ?/* Estimated stack frame consumption by the function. ?*/
>> >> ? ?HOST_WIDE_INT estimated_stack_size;
>> >> - ?/* Expected offset of the stack frame of inlined function. ?*/
>> >> - ?HOST_WIDE_INT stack_frame_offset;
>> >>
>> >> ? ?/* For inline clones this points to the function they will be
>> >> ? ? ? inlined into. ?*/
>> >> Index: gcc/ipa-inline.c
>> >> ===================================================================
>> >> --- gcc/ipa-inline.c ? ?(revision 174512)
>> >> +++ gcc/ipa-inline.c ? ?(working copy)
>> >> @@ -229,8 +229,6 @@ void
>> >> ?cgraph_clone_inlined_nodes (struct cgraph_edge *e, bool duplicate,
>> >> ? ? ? ? ? ? ? ? ? ? ? ? ? ? bool update_original)
>> >> ?{
>> >> - ?HOST_WIDE_INT peak;
>> >> -
>> >> ? ?if (duplicate)
>> >> ? ? ?{
>> >> ? ? ? ?/* We may eliminate the need for out-of-line copy to be output.
>> >> @@ -279,13 +277,13 @@ cgraph_clone_inlined_nodes (struct cgrap
>> >> ? ? ?e->callee->global.inlined_to = e->caller->global.inlined_to;
>> >> ? ?else
>> >> ? ? ?e->callee->global.inlined_to = e->caller;
>> >> - ?e->callee->global.stack_frame_offset
>> >> - ? ?= e->caller->global.stack_frame_offset
>> >> - ? ? ?+ inline_summary (e->caller)->estimated_self_stack_size;
>> >> - ?peak = e->callee->global.stack_frame_offset
>> >> - ? ? ?+ inline_summary (e->callee)->estimated_self_stack_size;
>> >> - ?if (e->callee->global.inlined_to->global.estimated_stack_size < peak)
>> >> - ? ?e->callee->global.inlined_to->global.estimated_stack_size = peak;
>> >> +
>> >> + ?/* Pessimistically assume no sharing of stack space. ?That is, the
>> >> + ? ? frame size of a function is estimated as the original frame size
>> >> + ? ? plus the sum of the frame sizes of all inlined callees. ?*/
>> >> + ?e->callee->global.inlined_to->global.estimated_stack_size +=
>> >> + ? ?inline_summary (e->callee)->estimated_self_stack_size;
>> >> +
>> >> ? ?cgraph_propagate_frequency (e->callee);
>> >>
>> >> ? ?/* Recursively clone all bodies. ?*/
>> >> @@ -430,8 +428,7 @@ cgraph_check_inline_limits (struct cgrap
>> >>
>> >> ? ?stack_size_limit += stack_size_limit * PARAM_VALUE
>> >> (PARAM_STACK_FRAME_GROWTH) / 100;
>> >>
>> >> - ?inlined_stack = (to->global.stack_frame_offset
>> >> - ? ? ? ? ? ? ? ? ?+ inline_summary (to)->estimated_self_stack_size
>> >> + ?inlined_stack = (to->global.estimated_stack_size
>> >> ? ? ? ? ? ? ? ? ? ?+ what->global.estimated_stack_size);
>> >> ? ?if (inlined_stack ?> stack_size_limit
>> >> ? ? ? ?&& inlined_stack > PARAM_VALUE (PARAM_LARGE_STACK_FRAME))
>> >> @@ -2064,7 +2061,6 @@ compute_inline_parameters (struct cgraph
>> >> ? ?self_stack_size = optimize ? estimated_stack_frame_size (node) : 0;
>> >> ? ?inline_summary (node)->estimated_self_stack_size = self_stack_size;
>> >> ? ?node->global.estimated_stack_size = self_stack_size;
>> >> - ?node->global.stack_frame_offset = 0;
>> >>
>> >> ? ?/* Can this function be inlined at all? ?*/
>> >> ? ?node->local.inlinable = tree_inlinable_function_p (node->decl);
>> >>
>> >
>