On Fri, 02 May 2008 17:50:53 -0700 Ian Lance Taylor (ILT) wrote: ILT> "Udo A. Steinberg" <us15@xxxxxxxxxxxxxxxxxxxx> writes: ILT> ILT> > gcc now complains about the following code snippet, saying... ILT> > warning: assuming pointer wraparound does not occur when comparing ILT> > P +- C1 with P +- C2 ILT> ILT> Presumably only when you use -Wstrict-overflow=N where N >= 3. At ILT> that level false positives are likely. Actually it warns at N >= 2. I'm using gcc version 4.4.0 20080428 (experimental) via: g++ -Os -Wstrict-overflow=2 foo.cpp ILT> > In the first snippet ptr never points outside x[], so the compiler ILT> > shouldn't warn. What am I missing here? ILT> ILT> Nothing. The compiler could be smarter here. pointer_may_wrap_p in ILT> fold-const.c could handle TREE_CODE (TREE_TYPE (base)) == ARRAY_TYPE. That would be nice. ILT> By the way, the compiler doesn't warn here: [...] ILT> because it doesn't know that putc doesn't change x, so it can't ILT> optimize away the comparison. Ahh ok! Thanks for the explanation. Cheers, - Udo
