On 2020/1/7 16:40, Jan Hubicka wrote:
>> On Mon, 2020-01-06 at 01:03 -0600, Xiong Hu Luo wrote:
>>> Inline should return failure either (newsize > param_large_function_insns)
>>> OR (newsize > limit). Sometimes newsize is larger than
>>> param_large_function_insns, but smaller than limit, inline doesn't return
>>> failure even if the new function is a large function.
>>> Therefore, param_large_function_insns and param_large_function_growth
>>> should be
>>> OR instead of AND, otherwise --param large-function-growth won't
>>> work correctly with --param large-function-insns.
>>>
>>> gcc/ChangeLog:
>>>
>>> 2020-01-06 Luo Xiong Hu <luo...@linux.ibm.com>
>>>
>>> ipa-inline-analysis.c (estimate_growth): Fix typo.
>>> ipa-inline.c (caller_growth_limits): Use OR instead of AND.
>> OK
>
> This patch also seems wrong. Inliner should return failure when
> newsize > param_large_function_insns && newsize > limit
> The reason is same as with large_unit_insns. We used to have only
> growth limits but it has turned out that this gets too
> restrictive/random for very small units/growths.
>
> So the logic is meant to be that inlining is OK either
> - if function is reasonably small (large_function_insns limit is not
> met)
> - or it does not grow too much (large-function-growth isnot met)
Sorry for checking too fast. Will revert once confirmed.
large_function_insns is default to 2700, and large-function-growth is
default to 100, so inline a large function with insn 2700 to another large
function with insn 2700 is allowed here (limit reach to 5400), I observed
HUGE performance drop in some cases for this behavior(large function inline
large function due to register spilling) compared with not inlined, that's
why this patch comes out.
>From performance point of view，it seems benefitial to inline small function to
large function, but negative when inline large function to large
function(causing
register spill)? 2700 seems too large for defining a function to be large and
and
5400 also seems too big for growth limit?
This inline happens at "Inlining one function called once", it's out of
inline_small_functions and since newsize > param_large_function_insns, so I
suppose it won't change behavior for inlining small functions?
>
> @item large-function-insns
> The limit specifying really large functions. For functions larger than
> this limit after inlining, inlining is constrained by @option{--param
> large-function-growth}. This parameter is useful primarily to avoid
> extreme compilation time caused by non-linear algorithms used by the
> back end.
>
>
> Honza
>> jeff
>>
