On Thu, Oct 1, 2015 at 3:01 PM, Richard Trieu <rtr...@google.com> wrote: > rtrieu added a comment. > > Next time, add > >> Differential Revision: <URL> > > > to your commit and Phabricator will close the diff automatically. > > http://llvm.org/docs/Phabricator.html > > > ================ > Comment at: lib/Analysis/CFG.cpp:99-104 > @@ +98,8 @@ > + // Currently we're only given EnumConstantDecls or IntegerLiterals > + auto *C1 = cast<EnumConstantDecl>(cast<DeclRefExpr>(A)->getDecl()); > + auto *C2 = cast<EnumConstantDecl>(cast<DeclRefExpr>(B)->getDecl()); > + > + const TagDecl *E1 = TagDecl::castFromDeclContext(C1->getDeclContext()); > + const TagDecl *E2 = TagDecl::castFromDeclContext(C2->getDeclContext()); > + return E1 == E2; > +} > ---------------- > george.burgess.iv wrote: >> rtrieu wrote: >> > There's a few extra casts in here, plus some blind conversions between >> > types. Add your assumptions for the types in asserts. Also, DeclContext >> > should use cast<> to get to Decl types. I recommend the following: >> > >> > ``` >> > assert(isa<DeclRefExpr>(E1) && isa<DeclRefExpr>(E2)); >> > auto *Decl1 = cast<DeclRefExpr>(E1)->getDecl(); >> > auto *Decl2 = cast<DeclRefExpr>(E2)->getDecl(); >> > >> > assert(isa<EnumConstantDecl>(Decl1) && isa<EnumConstantDecl>(Decl2)); >> > const DeclContext *DC1 = Decl1->getDeclContext(); >> > const DeclContext *DC2 = Decl2->getDeclContext(); >> > >> > assert(isa<EnumDecl>(DC1) && isa<EnumDecl>(DC2)); >> > return DC1 == DC2; >> > >> > ``` >> I was under the impression that the `cast<Foo>(Bar)` asserts `isa<Foo>(Bar)` >> for me, so I thought that asserts like those would just be redundant. >> Changed to your version anyway :) > You are correct, 'cast<Foo>(Bar)' does assert 'isa<Foo>(Bar)'. However, when > Bar is not Foo, using the assert here means the crash will produce a > backtrace will point straight to this function instead of an assert that > points deep into the casting functions.
Doubling the expense for assert builds so that we get a slightly better stack trace in the event our assumptions are wrong doesn't seem like a good tradeoff. It means everyone running an assert build pays the price twice to save a few moments of scanning the backtrace in a situation that's (hopefully) highly unlikely to occur in practice. ~Aaron > > > http://reviews.llvm.org/D13157 > > > _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
