On Thu, May 19, 2016 at 9:28 AM, Richard Biener <richard.guent...@gmail.com> wrote: > On Thu, May 19, 2016 at 3:19 PM, Jason Merrill <ja...@redhat.com> wrote: >> On Thu, May 19, 2016 at 12:30 AM, Basile Starynkevitch >> <bas...@starynkevitch.net> wrote: >>> On 05/19/2016 12:12 AM, Jeff Law wrote: >>>> >>>> On 05/17/2016 04:01 PM, David Malcolm wrote: >>>>> >>>>> There have been requests [1] for libgccjit to better support >>>>> functional programming by supporting the contination-passing style, >>>>> in which every function "returns" by calling a "continuation" >>>>> function pointer. >>>>> >>>>> These calls must be guaranteed to be implemented as a jump, >>>>> otherwise the program could consume an arbitrary amount of stack >>>>> space as it executed. >>>>> >>>>> This patch kit implements this. >>>>> >>>>> Patch 1 is a preliminary tweak to calls.c >>>>> >>>>> Patch 2 implements a new flag in tree.h: CALL_EXPR_MUST_TAIL_CALL, >>>>> which makes calls.c try harder to implement a flagged call as a >>>>> tail-call/sibling call, and makes it issue an error if >>>>> the optimization is impossible. It doesn't implement any >>>>> frontend support for setting the flag (instead using a plugin >>>>> to test it). We had some discussion on the jit list about possibly >>>>> introducing a new builtin for this, but the patch punts on this >>>>> issue. >>>> >>>> I wonder if we should have an attribute so that the flag can be set for >>>> C/C++ code. I've seen requests for forcing tail calls in C/C++ code >>>> several >>>> times in the past, precisely to support continuations. >>> >>> Why an attribute? Attributes are on declarations. I think it should better >>> be some pragma like _Pragma(GCC tail cail, foo(x,y)) or some builtin (or >>> else some syntax extension like goto return foo(x,y); ...) because what we >>> really want is to annotate a particular call to be tail-recursive. >> >> C++11 attributes can apply to expression-statements as well, e.g. >> >> [[gnu::tail_call]] fn(); >> >> though not to sub-expressions. > > That's nice. Can they apply to things like loops? > > [[gnu::no_unroll]] for (int i=0; i<4; ++i) > a[i] = 0;
Yes, to any statement. Jason
