[Soot-list] JimpleLocal.equals()

[Ondřej Lhoták]

Local variables do not have any internal substructure (i.e.
subexpressions).

equivTo is used for equivalent expressions for the purpose of things
like common subexpression elimination. Two locals are equivalent if
and only if they are the same local.

The previous implementation compared the names of the locals. This is
incorrect in the case when multiple distinct locals have the same name.
This can arise in Soot for example with the use-original-names option.

Ondřej

On Mon, Jan 28, 2013 at 04:04:40PM -0500, Patrick Lam wrote:
> Version control history shows me that Ondrej made that change in 2003:
> 
> plam at polya:~/soot-svn/src/soot/jimple/internal$ svn log -r705
> ------------------------------------------------------------------------
> r705 | olhota | 2003-03-02 18:14:13 -0500 (Sun, 02 Mar 2003) | 3 lines
> 
> Bug fix: equivTo on JimpleLocal's and BafLocal's should be object equality
> svn merge -r 703:704 $SVN/branches/1.2.5.dev.8
> 
> I'm not sure why this is the case. Maybe Ondrej remembers. It was 9
> years ago though.
> 
> pat
> 
> On 01/28/2013 03:04 PM, Michael Faes wrote:
> >Hi everyone,
> >
> >I'm currently having problems with the implementation of
> >JimpleLocal.equals() and equivTo():
> >
> >/**
> >   * Returns true if the given object is structurally equal to this one.
> >   */
> >public boolean equivTo(Object o) {
> >      return this.equals( o );
> >}
> >
> >While the Javadoc says that structural equivalence is tested (which is a
> >sensible thing to do), actually object identity is tested, as the
> >equals() method is not overridden (which does not seem to be so
> >sensible). In addition, the hashCode() method is overridden in a
> >structure-based way, which (is legal but) makes even less sense to me.
> >
> >Does anybody know if there is a reason for all this or can I safely
> >replace the current equals method with a structure-based one?
> >
> >Thanks for your time.
> >Michael
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>