http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56982
--- Comment #14 from Mikael Pettersson <mikpe at it dot uu.se> --- (In reply to Bernd Edlinger from comment #13) > Created attachment 30431 [details] > another example of wrong compilation > > This is another example where the optimization can > go wrong. > > The attached program produces expected results if > compiled with -O0: > x=0, a=1 > x=1, a=1 > a=1 > > But if compiled with -O3 and if the value "a" is placed > in a register the result is like this: > x=0, a=1 > x=1, a=0 > a=0 > > That is because longjmp has more semantic than just a branch: > It branches to the setjmp, and restores all callee saved registers to > the previos value. Your example is invalid C. Referring to WG14 n1494.pdf (there may be more recent C1x documents, but it's the one I had available right now): - you violate 7.13.1.1 which specifies where setjmp() may be called, an assignment statement is not one of the permitted contexts - more importantly, your auto variable a is not volatile-qualified, which means that its value is indeterminate after the longjmp (7.13.2.1). Please fix these issues and check again if it yields wrong results.
