On Wed, Nov 5, 2014 at 10:45 PM, Andrew Stubbs <a...@codesourcery.com> wrote: > This patch adds the following warning message: > > undefined.c:9:20: warning: statement may be undefined in the final loop > iteration. [-Waggressive-loop-optimizations] > for (i = 0; array[i] && i < 5; i++) > ^ > > (Where the code ought to read "i < 5 && array[i]".) > > The tree-ssa loop optimizations already eliminate useless loop-exit > conditions (i.e. conditions that will never be true). Unfortunately, they > also eliminate exit conditions that can be true, but only after undefined > behaviour has occurred. Typically, that means that the undefined behaviour > becomes an infinite loop (if it doesn't happen to crash, of course), and > that's surprising. It also looks more like a compiler bug than a crash does. > > The new warning should highlight these cases but does not actually change > anything. I've included a comment where the compiler could be adjusted to > avoid the surprising optimization. Would it be appropriate to do so? > > OK to commit?
Please find a better way to communicate possibly_undefined_stmt than enlarging struct loop. Like associating it with the niter bound we record (so you can also have more than one). Thanks, Richard. > Andrew
