Umashankar V.K. wrote: > I have few questions about inbuilt mechanism of gcc/g++ for > warning about uninitialized variable. > > I am interested in cases where compiler is unable to warn. I am > aware that all the known bugs about warning-failure are > mentioned at bugzilla http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639 > > a) The compiler activates the warning mechanism only if optimisation > is enabled at compilation time with -O option. > For all the bugs that I went through at bugzilla, the failure is not > -O level dependent. The warning-failure occurs for all levels of > optimisation. > So, I believe this is the general case. > > But then I came across the following failure case. This one fails > to warn when compiled with any level below 3. > With -O3, gcc is able to warn. Can someone tell me which is the > corresponding bug logged at bugzilla ? I don't understand why you think this is a bug in gcc. Inlining will always reveal more about the data flow of a program. > Are there any more such bugs which disappear when compiled with > specific -O level ? > > b) Are there any known "fail to do uninitialised-warning" gcc bugs > which are language-dependent ? If there is an uninitialized variable, and gcc fails to notice, that is not necessarily a bug. For example, extern void foo (int *p); void bar { int a; foo (&a); printf("%d\n", a); } We could fix gcc so that in every case where we couldn't prove that a variable is initialized, we warned. You'd have to put up with a lot of spurious "may be used uninitialized" warnings. Andrew.
