[C++11][4.9] Add missing REDUC_PLUS_EXPR case to potential_constant_expression_1.

[James Greenhalgh]

Hi Richard,

Thanks for your feedback. This does feel like a much nicer solution now.

> Yes, it looks basically ok.  I'd probably restrict it to folding target
> builtins
> though - similar to what TARGET_FOLD_BUILTIN did.  Exactly to not
> expose all stmts to the backends.  That is, move the target hook call
> to gimple_fold_call, after the inplace check (and remove the inplace
> argument of the target hook), and call it only for DECL_BUILT_IN_CLASS
> BUILT_IN_MD.

This seems sensible - hopefully something like the attached will be
closer to an acceptable implementation. The aarch64 portion certainly
looks much cleaner now.
 
> Not sure if TARGET_FOLD_STMT is then still an appropriate name ...
> TARGET_FOLD_BUILTIN is already taken unfortunately.  Maybe
> TARGET_FOLD_BUILTIN_MD_CALL?

I've gone for TARGET_GIMPLE_FOLD_BUILTIN (to fit with the
non-target-specific gimple_fold_builtin).

I've also updated the documentation for TARGET_FOLD_BUILTIN to
make it clear that the tree returned must be valid in GENERIC
and GIMPLE.

Thanks again for your help.

James
Graduate Engineer
ARM.

---
gcc/

2013-04-19  James Greenhalgh  <james.greenhalgh@arm.com>

	* coretypes.h (gimple_stmt_iterator_d): Forward declare.
	(gimple_stmt_iterator): New typedef.
	* gimple.h (gimple_stmt_iterator): Rename to...
	(gimple_stmt_iterator_d): ... This.
	* doc/tm.texi.in (TARGET_FOLD_BUILTIN): Detail restriction that
	trees be valid for GIMPLE and GENERIC.
	(TARGET_GIMPLE_FOLD_BUILTIN): New.
	* gimple-fold.c (gimple_fold_call): Call target hook
	gimple_fold_builtin.
	* hooks.c (hook_bool_gsiptr_false): New.
	* hooks.h (hook_bool_gsiptr_false): New.
	* target.def (fold_stmt): New.
	* doc/tm.texi: Regenerate.

2013-04-19  James Greenhalgh  <james.greenhalgh@arm.com>

	* config/aarch64/aarch64-builtins.c
	(aarch64_fold_builtin): Move folds to gimple-specific tree codes
	to aarch64_gimple_fold_builtin.
	(aarch64_gimple_fold_builtin): New.
	* config/aarch64/aarch64-protos.h (aarch64_gimple_fold_builtin): New.
	* config/aarch64/aarch64.c (TARGET_GIMPLE_FOLD_BUILTIN): Define.
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