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. Jason
