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Re: Designs for better debug info in GCC


Alexandre Oliva <aoliva@redhat.com> writes:

> On Dec 19, 2007, Ian Lance Taylor <iant@google.com> wrote:
> 
> > For some things, sure, but we are just talking about the values in
> > user visible variables stored in registers.  There is no way we can
> > make that information be correct between line notes.
> 
> Err...  I think there is, and one way to do it is with the design I've
> proposed.  Do you have anything to back up your implied assertion that
> the design can't accomplish this?

It is technically feasible but problematic for other reasons.
    i = i * m + ((i / j) + k) / n;
On a two register machine like the x86 i will change several times
during that calculation.  You could issue debug notes making it
correct at every machine instruction.  But that would balloon the
amount of debug info that we generate, for near-zero gain in real
usability of the debugger.  We already generate huge amounts of debug
info--a typical C++ executable has more debug info than text and data
combined.  Increasing the amount of debug info significantly, for
little gain, is contraindicated.

Ian


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