Hi, On Wed, 4 May 2011, Richard Kenner wrote:
> > There are pros and cons about early optimization, actually. > > Generating extremely optimized IL very early can actually tie up > > subsequent passes. For instance, loop unrolling and vectorization. > > There are others in the literature. > > Sure, in the sorts of examples you mention where there's a level of > "globality" to it. But I don't see it in the types of things that > fold does. How could it ever be better to leave "a - a" in the tree > instead of "0"? The former is not a constant expression in the C sense, hence folding it early disables required diagnostics; that's what Joseph means when he says that the frontends should fold only exactly those things that the language standard requires, implying not a general catch-all folder. After the frontend is ready with a construct we can do all kinds of foldings as early as we like. Ciao, Michael.
