On Fri, Oct 2, 2015 at 1:40 AM, Geert Bosch <bos...@mac.com> wrote: > >> On Oct 1, 2015, at 11:34 AM, Alexander Monakov <amona...@ispras.ru> wrote: >> >> Can you expand on the "etc." a bit, i.e., may the compiler ... >> >> - move a call to a "const" function above a conditional branch, >> causing a conditional throw to happen unconditionally? > No, calls may only be omitted, not moved. >> >> - move a call to a "const" function below a conditional branch, >> causing an unconditional throw to happen only conditionally? >> No, calls may only be omitted, not moved.
I think that's less clear as the transform basically duplicates the call on both branches and removes the one that is not necessary. >> - reorder calls to "const" functions w.r.t. code with side effects, or >> other throwing functions? > A call to a pure function (Ada's version of "const") may be omitted if its > result is not used, > or if results of an earlier call with the same argument values (including > referenced values) can > be used. This is allowed regardless of whether the original function had any > side effects. > Note that if a function raised an exception (threw) the call can only be > replaced with throwing > that exception. > > So, reordering is not allowed, but omitting is, in the context of Ada. I think GCC does both though (if it throws only externally, for internally throwing ones the transforms would be too complicated). Richard. > -Geert >
