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

[Richard Biener <rguenther at suse dot de>]

On Thu, 16 Apr 2015, Tom de Vries wrote:

> [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 .

Ok.

Thanks,
Richard.

> 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.