jlh wrote:
docs> ...so deleting them will not make real programs run any faster. docs> However, the rationale here is that optimization of a nonempty docs> loop cannot produce an empty one, which holds for C but is not docs> always the case for C++.
This is the part I don't get. Why can the optimization of a C loop never yield an empty loop? Take this trivial example:
Of course no-one would write this, but it's an example where an
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ you've answered your own question. The writer of the docs meant to say 'holds for C written by someone who is careful and compiled by __DATE__ era compilers'. Unfortunately
1) programmers' concentration can slip
2) optimizers have become more powerful
For C++, the docs say that things are different. Here's another example, that is somewhat more realistic. First we define a function
What's being hinted at is that the definition A ary[50]; needs to emit code to construct the elements, that will be a loop. If the ctor turns out to be a nop, the loop should evaporate.
The documentation needs revising, methinks
nathan
-- Nathan Sidwell :: http://www.codesourcery.com :: CodeSourcery LLC nathan@xxxxxxxxxxxxxxxx :: http://www.planetfall.pwp.blueyonder.co.uk
