On Nov 1, 2012, Jakub Jelinek <ja...@redhat.com> wrote: > Even for stmt frontiers it is IMHO undesirable to duplicate > (perhaps many times) the whole sequence, as one would then reply the var > changing sequence in the debugger perhaps once in the original bb, then > once or many times again in the successor bb.
Quite the opposite: when we do jump threading, we're *bypassing* the entire block, so in order to retain proper history we'd have to propagate all the source-expected changes into the short-circuited path. To wit, we start with a computation log like this: jump to block A A: # set foo to expr1 # advance to line n # set foo to expr2 jump to block B B: # advance to line m # set foo to expr3 in which we can see foo bound to all 3 expressions, to a computation log like this: jump to block B B: # advance to line m # set foo to expr3 or: jump to block B B: # set foo to expr1 # advance to line n # set foo to expr2 # advance to line m # set foo to expr3 which ones seems like a more faithful representation of the computation described in the source code to you? -- Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/ You must be the change you wish to see in the world. -- Gandhi Be Free! -- http://FSFLA.org/ FSF Latin America board member Free Software Evangelist Red Hat Brazil Compiler Engineer
