On Fri, Jul 25, 2014 at 12:35, Richard Biener <richard.guent...@gmail.com> wrote: > On Fri, Jul 25, 2014 at 10:43 AM, Thomas Mertes <thomas.mer...@gmx.at> wrote: > > On Thu, Jul 24 at 10:36 PM, Richard Biener <richard.guent...@gmail.com> > > wrote: > >> Fact is that if somebody is interested in > >> -ftrapv he/she is welcome to contribute patches. Especially testing > >> coverage is poor. > > > > As I said I have test programs for integer overflow (not written > > in C). Now I have converted one test program to C. This program > > checks if an int64_t overflow raises SIGABRT or SIGILL. The name of > > the program is chkovf64.c and I have uploaded it to > > > > http://sourceforge.net/projects/seed7/files/ > > > > It is licenced with GPL. You can use it to improve the testing > > coverage of gcc. When I compile it with: > > > > gcc -ftrapv chkovf64.c -o chkovf64 > > > > it writes a lot of warnings about "integer overflow in expression". > > Running chkovf64 shows that -ftrapv does not work correct. > > That's https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61893 - basically > as soon as we can constant-fold we lose the trap. Which is probably > not important for practical purposes, but you have a point here.
For human programmers it is probably ok to have a warning instead of the trap. But when the C program has been generated (C as intermediate language) it is important that the trap is not lost. Isn't possible that constant-fold has the result "it will overflow"? Hopefully it is not necessary to omit an optimization because of -ftrapv. For my use-case that would be bad. I need -ftrapv together with all optimizations for production code and NOT for debugging purposes. > > Maybe all -ftrapv problems uncovered by chkovf64.c are because > > of this. Unfortunately there are also other test cases where > > a signal is not raised although a signed integer overflow occurred. > > This happens in a much bigger program and until now I was not > > able to create a simple test case from it. > > Yes, not all optimizations may be aware of -ftrapv. In the case above (the much bigger program) the error (overflow without raising SIGABRT) happens when I compile without -O and without -g. When I use -g the signal SIGABRT is raised. I still don't have a simple test case, sorry. Did you have a look at chkovf64.c? Is it useable as test program for -ftrapv? Greetings Thomas Mertes -- Seed7 Homepage: http://seed7.sourceforge.net Seed7 - The extensible programming language: User defined statements and operators, abstract data types, templates without special syntax, OO with interfaces and multiple dispatch, statically typed, interpreted or compiled, portable, runs under linux/unix/windows.
