[PING^2] [PATCH][5a/5] Postpone expanding va_arg until pass_stdarg

[Tom de Vries <Tom_deVries@mentor.com>]

[stage1 ping^2]
On 10-03-15 16:30, Tom de Vries wrote:
> [stage1 ping]
> On 22-02-15 14:13, Tom de Vries wrote:
>> On 19-02-15 14:03, Richard Biener wrote:
>>> On Thu, 19 Feb 2015, Tom de Vries wrote:
>>>
>>>> On 19-02-15 11:29, Tom de Vries wrote:
>>>>> Hi,
>>>>>
>>>>> I'm posting this patch series for stage1:
>>>>> - 0001-Disable-lang_hooks.gimplify_expr-in-free_lang_data.patch
>>>>> - 0002-Add-gimple_find_sub_bbs.patch
>>>>> - 0003-Factor-optimize_va_list_gpr_fpr_size-out-of-pass_std.patch
>>>>> - 0004-Handle-internal_fn-in-operand_equal_p.patch
>>>>> - 0005-Postpone-expanding-va_arg-until-pass_stdarg.patch
>>>>>
>>>>> The patch series - based on Michael's initial patch - postpones expanding
>>>>> va_arg
>>>>> until pass_stdarg, which makes pass_stdarg more robust.
>>>>>
>>>>> Bootstrapped and reg-tested on x86_64 using all languages, with unix/ and
>>>>> unix/-m32 testing.
>>>>>
>>>>> I'll post the patches in reply to this email.
>>>>>
>>>>
>>>> This patch postpones expanding va_arg until pass_stdarg.
>>>>
>>>> We add a new internal function IFN_VA_ARG. During gimplification, we map
>>>> VA_ARG_EXPR onto a CALL_EXPR with IFN_VA_ARG, which is then gimplified in to a
>>>> gimple_call. At pass_stdarg, we expand the IFN_VA_ARG gimple_call into actual
>>>> code.
>>>>
>>>> There are a few implementation details worth mentioning:
>>>> - passing the type beyond gimplification is done by adding a NULL pointer-
>>>>    to-type to IFN_VA_ARG.
>>>> - there is special handling for IFN_VA_ARG that would be most suited to be
>>>>    placed in gimplify_va_arg_expr. However, that function lacks the scope for
>>>>    the special handling, so it's placed awkwardly in gimplify_modify_expr.
>>>> - there's special handling in case the va_arg type is variable-sized.
>>>>    gimplify_modify_expr adds a WITH_SIZE_EXPR to the CALL_EXPR IFN_VA_ARG for
>>>>    variable-sized types. However, this is gimplified into a gimple_call which
>>>>    does not have the possibility to wrap it's result in a WITH_SIZE_EXPR. So
>>>>    we're adding the size argument of the WITH_SIZE_EXPR as argument to
>>>>    IFN_VA_ARG, and at expansion in pass_stdarg, wrap the result of the
>>>>    gimplification of IFN_VA_ARG in a WITH_SIZE_EXPR, such that the subsequent
>>>>    gimplify_assign will generate a memcpy if necessary.
>>>> - when gimplifying the va_arg argument ap, it may not be addressable. So
>>>>    gimplification will generate a copy ap.1 = ap, and use &ap.1 as argument.
>>>>    This means that we have to copy back the ap.1 value to ap after IFN_VA_ARG.
>>>>    The copy is classified by the va_list_gpr/fpr_size optimization as an
>>>>    escape,  so it inhibits optimization. The tree-ssa/stdarg-2.c f15 update is
>>>>    because of that.
>>>>
>>>> OK for stage1?
>>>
>>> Looks mostly good, though it looks like with -O0 this doesn't delay
>>> lowering of va-arg and thus won't "fix" offloading.  Can you instead
>>> introduce a PROP_gimple_lva, provide it by the stdarg pass and add
>>> a pass_lower_vaarg somewhere where pass_lower_complex_O0 is run
>>> that runs of !PROP_gimple_lva (and also provides it), and require
>>> PROP_gimple_lva by pass_expand?  (just look for PROP_gimple_lcx for
>>> the complex stuff to get an idea what needs to be touched)
>>>
>>
>> Updated according to comments.
>>
>> Furthermore (having updated the patch series to recent trunk), I'm dropping the
>> ACCEL_COMPILER bit in pass_stdarg::gate. AFAIU the comment there relates to this
>> patch.
>>
>> Retested as before.
>>
>> OK for stage1?
>>
>
> Ping.

Ping again.

Patch originally posted at: 
https://gcc.gnu.org/ml/gcc-patches/2015-02/msg01332.html .

Thanks,
- Tom

>> Btw, I'm wondering if as run-time optimization we can tentatively set
>> PROP_gimple_lva at the start of the gimple pass, and unset it in
>> gimplify_va_arg_expr. That way we would avoid the loop in expand_ifn_va_arg_1
>> (over all bbs and gimples) in functions without va_arg.
>>
>
> Taken care of in follow-up patch 5b.