From: iainf@spider.com (Iain A F Fleming) Newsgroups: comp.editors,comp.sys.transputer Subject: Re: Folding editors Date: 18 Nov 1998 11:01:24 +0000 Organization: Spider Software Ltd Sender: iainf@belhaven.spider.com Distribution: inet Message-Id: <6rk90t464b.fsf@belhaven.spider.com> References: <36374B57.168B9492@pact.srf.ac.uk> <71aj0c$oc$1@fangorn.moria.de> <6r1znq7264.fsf@belhaven.spider.com> <3639BEFD.2CC25E3C@esgem.com> <6r4ssm59ay.fsf@belhaven.spider.com> <6rhfwi4ee6.fsf@belhaven.spider.com> <363EEB84.5CAD538B@roke.co.uk> <6rvhkw20nk.fsf@belhaven.spider.com> <364CBB49.ABE8624B@oucs.ox.ac.uk> <6r90hb7vgg.fsf@belhaven.spider.com> <3651C1BA.16126C2@roke.co.uk> In-Reply-To: Richard Beton's message of Tue, 17 Nov 1998 18:34:34 +0000 Xref: ukc comp.editors:32298 comp.sys.transputer:8929 The entity calling itself Richard Beton wrote: > > I'm not sure whether the compiler optimisation is necessarily hindered by > deep folding, although with some languages and some compilers I wouldn't > be surprised. On the Transputer, efficiency of instruction coding (density) is affected by stack offset a variable is placed at. Deep nested blocks, with variables live across the inner blocks, hinders placing all heavily-used variables at lower slots (>16). Moving inner blocks to independent functions (in the Transputer C compiler, at least) could well reduce code size, and improve speed. (I know this as I wrote parts of both the inmos Occam & C compilers.) On other architecures, the equivalent cost will be register spilling. Also, determining data-flow in any program is always a worst-case. As you make the program more complicated, the more pessimistic the compiler will become. Common sub-expression analysis becomes less tractable. > In occam, the nesting depth would be no hindrance to compiler > optimisation and could possibly aid it. Assuming that you had an optimising Occam compiler. As far as I know the inmos optimising Occam compiler, although very good, never (officialy) escaped from Aztec West. -- Iain A F Fleming http://www.spider.com/ Spider Sofware Ltd Leith Scotland +44.131.475.7045