[PATCH][5/5] Postpone expanding va_arg until pass_stdarg

[Tom de Vries]

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?

Thanks,
- Tom

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