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

[James Greenhalgh <james dot greenhalgh at arm dot com>]

> -----Original Message-----
> From: dosreis@gmail.com [mailto:dosreis@gmail.com] On Behalf Of Gabriel
> Dos Reis
> Sent: 20 March 2013 19:09
> To: James Greenhalgh
> Cc: Jakub Jelinek; Richard Biener; gcc-patches@gcc.gnu.org; Jason
> Merrill; mark@codesourcery.com
> Subject: Re: [C++11][4.9] Add missing REDUC_PLUS_EXPR case to
> potential_constant_expression_1.
>
> On Wed, Mar 20, 2013 at 1:03 PM, James Greenhalgh
> <james.greenhalgh@arm.com> wrote:
>
> > Is that be sensible? It certainly seems like someone intended to
> > explicitly enumerate all the possible cases and ensure that they were
> > correctly handled.
>
> That someone would be me.
>
> We need to catch loudly any front-end tree code, e.g. ASTs, object
> we may have missed, as opposed to silently ignoring them with
> possible miscompilation and pray that someone might be sufficiently
> pissed off and report it as a bug.
>
> What is wrong isn't that the front-end inserts internal coverage
> check; rather it is the fact that we don't have enough separation
> between front-end asts and middle-end stuff.
>
> The convenience of adding a middle-end optimization (which this
> essentially is) should not trump correctness of the implementation
> of standard semantics.

So, as far as I can see no decision came out of this thread as to
what should be done. In that time I had to add another few tree cases
as I added more things to TARGET_FOLD_BUILTIN.

I'd like to start pushing some of these TARGET_FOLD_BUILTIN patches
upstream, but they currently all hinge on resolving this discussion.

Would it be OK for this patch to go in, I know the thread started
well for me with:

> -----Original Message-----
> From: Jason Merrill [mailto:jason@redhat.com]
> Sent: 14 March 2013 18:52
> To: James Greenhalgh; gcc-patches@gcc.gnu.org
> Cc: mark@codesourcery.com
> Subject: Re: [C++11][4.9] Add missing REDUC_PLUS_EXPR case to
> potential_constant_expression_1.
>
> On 03/14/2013 09:48 AM, James Greenhalgh wrote:
> > Is this OK to commit to 4.9 when stage 1 opens up?
>
> Yes, but please add the other new tree codes as well.
>
> Jason

But quickly moved on to discussion, so I didn't commit the patch.

Thanks,
James Greenhalgh
Graduate Engineer
ARM

---
gcc/

2013-04-09  James Greenhalgh  <james.greenhalgh@arm.com>

	* cp/semantics.c
	(potential_constant_expression_1): Add cases for REDUC_PLUS_EXPR,
	REDUC_MIN_EXPR, REDUC_MAX_EXPR.

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 72b884e..880f479 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -8619,6 +8619,9 @@ potential_constant_expression_1 (tree t, bool want_rval, tsubst_flags_t flags)
     case ABS_EXPR:
     case TRUTH_NOT_EXPR:
     case FIXED_CONVERT_EXPR:
+    case REDUC_PLUS_EXPR:
+    case REDUC_MIN_EXPR:
+    case REDUC_MAX_EXPR:
     case UNARY_PLUS_EXPR:
       return potential_constant_expression_1 (TREE_OPERAND (t, 0), rval,
 					      flags);