move increase_alignment from simple to regular ipa pass

On 14 June 2016 at 18:31, Prathamesh Kulkarni
<prathamesh.kulkarni@linaro.org> wrote:
> On 13 June 2016 at 16:13, Jan Hubicka <hubicka@ucw.cz> wrote:
>>> diff --git a/gcc/cgraph.h b/gcc/cgraph.h
>>> index ecafe63..41ac408 100644
>>> --- a/gcc/cgraph.h
>>> +++ b/gcc/cgraph.h
>>> @@ -1874,6 +1874,9 @@ public:
>>>       if we did not do any inter-procedural code movement.  */
>>>    unsigned used_by_single_function : 1;
>>>
>>> +  /* Set if -fsection-anchors is set.  */
>>> +  unsigned section_anchor : 1;
>>> +
>>>  private:
>>>    /* Assemble thunks and aliases associated to varpool node.  */
>>>    void assemble_aliases (void);
>>> diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
>>> index 4bfcad7..e75d5c0 100644
>>> --- a/gcc/cgraphunit.c
>>> +++ b/gcc/cgraphunit.c
>>> @@ -800,6 +800,9 @@ varpool_node::finalize_decl (tree decl)
>>>       it is available to notice_global_symbol.  */
>>>    node->definition = true;
>>>    notice_global_symbol (decl);
>>> +
>>> +  node->section_anchor = flag_section_anchors;
>>> +
>>>    if (TREE_THIS_VOLATILE (decl) || DECL_PRESERVE_P (decl)
>>>        /* Traditionally we do not eliminate static variables when not
>>>        optimizing and when not doing toplevel reoder.  */
>>> diff --git a/gcc/common.opt b/gcc/common.opt
>>> index f0d7196..e497795 100644
>>> --- a/gcc/common.opt
>>> +++ b/gcc/common.opt
>>> @@ -1590,6 +1590,10 @@ fira-algorithm=
>>>  Common Joined RejectNegative Enum(ira_algorithm) Var(flag_ira_algorithm) Init(IRA_ALGORITHM_CB) Optimization
>>>  -fira-algorithm=[CB|priority] Set the used IRA algorithm.
>>>
>>> +fipa-increase_alignment
>>> +Common Report Var(flag_ipa_increase_alignment) Init(0) Optimization
>>> +Option to gate increase_alignment ipa pass.
>>> +
>>>  Enum
>>>  Name(ira_algorithm) Type(enum ira_algorithm) UnknownError(unknown IRA algorithm %qs)
>>>
>>> @@ -2133,7 +2137,7 @@ Common Report Var(flag_sched_dep_count_heuristic) Init(1) Optimization
>>>  Enable the dependent count heuristic in the scheduler.
>>>
>>>  fsection-anchors
>>> -Common Report Var(flag_section_anchors) Optimization
>>> +Common Report Var(flag_section_anchors)
>>>  Access data in the same section from shared anchor points.
>>>
>>>  fsee
>>> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
>>> index a0db3a4..1482566 100644
>>> --- a/gcc/config/aarch64/aarch64.c
>>> +++ b/gcc/config/aarch64/aarch64.c
>>> @@ -8252,6 +8252,8 @@ aarch64_override_options (void)
>>>
>>>    aarch64_register_fma_steering ();
>>>
>>> +  /* Enable increase_alignment pass.  */
>>> +  flag_ipa_increase_alignment = 1;
>>
>> I would rather enable it always on targets that do support anchors.
> AFAIK aarch64 supports section anchors.
>>> diff --git a/gcc/lto/lto-symtab.c b/gcc/lto/lto-symtab.c
>>> index ce9e146..7f09f3a 100644
>>> --- a/gcc/lto/lto-symtab.c
>>> +++ b/gcc/lto/lto-symtab.c
>>> @@ -342,6 +342,13 @@ lto_symtab_merge (symtab_node *prevailing, symtab_node *entry)
>>>       The type compatibility checks or the completing of types has properly
>>>       dealt with most issues.  */
>>>
>>> +  /* ??? is this assert necessary ?  */
>>> +  varpool_node *v_prevailing = dyn_cast<varpool_node *> (prevailing);
>>> +  varpool_node *v_entry = dyn_cast<varpool_node *> (entry);
>>> +  gcc_assert (v_prevailing && v_entry);
>>> +  /* section_anchor of prevailing_decl wins.  */
>>> +  v_entry->section_anchor = v_prevailing->section_anchor;
>>> +
>> Other flags are merged in lto_varpool_replace_node so please move this there.
> Ah indeed, thanks for the pointers.
> I wonder though if we need to set
> prevailing_node->section_anchor = vnode->section_anchor ?
> IIUC, the function merges flags from vnode into prevailing_node
> and removes vnode. However we want prevailing_node->section_anchor
> to always take precedence.
>>> +/* Return true if alignment should be increased for this vnode.
>>> +   This is done if every function that references/referring to vnode
>>> +   has flag_tree_loop_vectorize set.  */
>>> +
>>> +static bool
>>> +increase_alignment_p (varpool_node *vnode)
>>> +{
>>> +  ipa_ref *ref;
>>> +
>>> +  for (int i = 0; vnode->iterate_reference (i, ref); i++)
>>> +    if (cgraph_node *cnode = dyn_cast<cgraph_node *> (ref->referred))
>>> +      {
>>> +     struct cl_optimization *opts = opts_for_fn (cnode->decl);
>>> +     if (!opts->x_flag_tree_loop_vectorize)
>>> +       return false;
>>> +      }
>>
>> If you take address of function that has vectorizer enabled probably doesn't
>> imply need to increase alignment of that var. So please drop the loop.
>>
>> You only want function that read/writes or takes address of the symbol. But
>> onthe other hand, you need to walk all aliases of the symbol by
>> call_for_symbol_and_aliases
>>> +
>>> +  for (int i = 0; vnode->iterate_referring (i, ref); i++)
>>> +    if (cgraph_node *cnode = dyn_cast<cgraph_node *> (ref->referring))
>>> +      {
>>> +     struct cl_optimization *opts = opts_for_fn (cnode->decl);
>>> +     if (!opts->x_flag_tree_loop_vectorize)
>>> +       return false;
>>> +      }
>>> +
>>> +  return true;
>>> +}
>>> +
>>>  /* Entry point to increase_alignment pass.  */
>>>  static unsigned int
>>>  increase_alignment (void)
>>> @@ -914,9 +942,12 @@ increase_alignment (void)
>>>        tree decl = vnode->decl;
>>>        unsigned int alignment;
>>>
>>> -      if ((decl_in_symtab_p (decl)
>>> -       && !symtab_node::get (decl)->can_increase_alignment_p ())
>>> -       || DECL_USER_ALIGN (decl) || DECL_ARTIFICIAL (decl))
>>> +      if (!vnode->section_anchor
>>> +       || (decl_in_symtab_p (decl)
>>> +           && !symtab_node::get (decl)->can_increase_alignment_p ())
>>> +       || DECL_USER_ALIGN (decl)
>>> +       || DECL_ARTIFICIAL (decl)
>>> +       || !increase_alignment_p (vnode))
>>
>> Incrementally we probably should do more testing whether the variable looks like
>> someting that can be vectorized, i.e. it contains array, has address taken or the
>> accesses are array accesses within loop.
>> This can be done by the analysis phase of the IPA pass inspecting the function
>> bodies.
> Thanks, I will try to check for array accesses are within a loop in
> followup patch.
> I was wondering if we could we treat a homogeneous global struct
> (having members of one type),
> as a global array of that type and increase it's alignment if required ?
>>
>> I think it is important waste to bump up everything including error messages etc.
>> At least on i386 the effect on firefox datasegment of various alignment setting is
>> very visible.
> Um for a start, would it be OK to check if all functions referencing variable
> have attribute noreturn, and in that case we skip increasing the alignment ?
> I suppose that error functions would be having attribute noreturn set ?
>>
>> Looks OK to me otherwise. please send updated patch.
> I have done the changes in the attached patch (stage-1 built).
> I am not sure what to return from the callback function and
> arbitrarily chose to return true.
Hi,
In this version (stage-1 built), I added read/write summaries which
stream those variables
which we want to increase alignment for.

I have a few questions:

a) To check if global var is used inside a loop, I obtained
corresponding ipa_ref
and checked loop_containing_stmt (ref->stmt), however it returned non-NULL
even when ref->stmt was not inside a loop.
for instance:
int a[32];
int f() { int x = a[0]; return x; }
Um how to check if stmt is used inside a loop ?

b) Is it necessary during WPA to check if function has
flag_tree_vectorize_set since
during analysis phase in increase_alignment_generate_summary() I check
if cnode has flag_tree_loop_vectorize_set ?

c) In LTO_increase_alignment_section, the following is streamed:
i) a "count" of type uwhi, to represent number of variables
ii) decls corresponding to the variables
The variables are then obtained during read_summay using
symtab_node::get_create().
I suppose since decls for varpool_nodes would already be streamed in
LTO_section_decls, I was wondering if I
could somehow refer to the decls in that section to avoid duplicate
streaming of decls ?

Thanks,
Prathamesh
>
> Thanks,
> Prathamesh
>>
>> Honza

move increase_alignment from simple to regular ipa pass

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