On Tue, 19 Dec 2006, Ian Lance Taylor wrote: > Here is a quick list of optimizations that mainline gcc performs which > rely on the idea that signed overflow is undefined. All the types > are, of course, signed. I made have made some mistakes. I think this > gives a good feel for the sorts of optimizations we can make with this > assumption.
Thanks for compiling this exhaustive list, Ian! Currently our documentation on -fwrapv is rather short and does not provide examples or anything to provide such a feel: This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction and multiplication wraps around using twos-complement representation. This flag enables some optimizations and disables others. This option is enabled by default for the Java front-end, as required by the Java language specification. "This flag enables some optimizations and disables others" is all we have. I wonder whether you could perhaps add (part of) your list to this documentation? Or would that be too specific? Gerald
