Etienne Lorrain wrote:
Hello,A lot of people (me too) write this kind of code: struct param1_str *param1; struct param2_str *param2; struct param3_str *param3; error = treat_alpha (param1, param2, param3); if (error) printf ("treat_alpha failed error %d, param1 = %p, " "param2 = %p, param3 = %p", error, param1, param2, param3); error = treat_beta (param1, param2, param3); if (error) printf ("treat_beta failed error %d, param1 = %p, " "param2 = %p, param3 = %p", error, param1, param2, param3); The printf() is only there for debug purposes, sometimes it is msglog() or even sprintf(). This construct cannot be optimised efficiently by the compiler because the variable list of parameters of printf() is not typed - so no "const" attribute, and even a simple: printf ("error %d\n", error); need to flush every registers to memory before the call and reload everything after the call.
In general this is not possible because of %n and because uppercase specifiers have undefined results (and can indeed be attached to arbitrary code using glibc). It may be possible to use the existing machinery to analyze format strings, and do the optimization you want in the case of constant format strings that don't mention uppercase specifiers or %n, but I am not knowledgeable enough to tell you if it is easy to do so or not.
Paolo
