On Wed, Sep 06, 2017 at 10:55:43PM -0400, Christopher Li wrote: > On Wed, Sep 6, 2017 at 10:15 PM, Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > Even this is not the case. > > > > Not for a C compiler, it isn't. > > > > Sure, if you do compilers for toy languages, it might be, but a C > > compiler has things like "switch()" statements that may not nest with > > loops etc. So even without a goto, you can pretty much have arbitrary > > flow. > > I am trying to think if without goto statement, can we create irreducible > graph. The for reducible graph, finding dominator has fast path. Bah ... Depending on the algorithm you use, irreducible graphs may indeed be a bit faster to calculate but since you don't know in advance if your graph is reducible or not, you can't take advantage of that. So, at least to me, this doesn't make it a fast path. > On way to look at the Simple SSA paper is that, it is taking advanctage > of that fast path. No. It takes advantage at every point where it is known that all the parents have already been processed. That's all. The part where reducibility matter is after the conversion is done, if you whish to simplify what they call trivial phi-nodes. And again, since you don't know in advance if your graph is reducible or not, there is no fast path. -- Luc -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
