On Mon, 15 Oct 2012, Dodji Seketeli wrote: > Hello, > > While reading alias.c, it seemed to me that some comments could use > some cleanups. > > OK for trunk?
Ok. Thanks, Richard. > Thanks. > > gcc/ > > * alias.c: Cleanup comments. > --- > gcc/alias.c | 27 +++++++++++++-------------- > 1 file changed, 13 insertions(+), 14 deletions(-) > > diff --git a/gcc/alias.c b/gcc/alias.c > index 0c6a744..09aef11 100644 > --- a/gcc/alias.c > +++ b/gcc/alias.c > @@ -60,14 +60,13 @@ along with GCC; see the file COPYING3. If not see > struct Z z2, *pz; > > > - py = &px1.y1; > + py = &x1.y1; > px2 = &x1; > > Consider the four questions: > > Can a store to x1 interfere with px2->y1? > Can a store to x1 interfere with px2->z2? > - (*px2).z2 > Can a store to x1 change the value pointed to by with py? > Can a store to x1 change the value pointed to by with pz? > > @@ -78,24 +77,24 @@ along with GCC; see the file COPYING3. If not see > a store through a pointer to an X can overwrite any field that is > contained (recursively) in an X (unless we know that px1 != px2). > > - The last two of the questions can be solved in the same way as the > - first two questions but this is too conservative. The observation > - is that in some cases analysis we can know if which (if any) fields > - are addressed and if those addresses are used in bad ways. This > - analysis may be language specific. In C, arbitrary operations may > - be applied to pointers. However, there is some indication that > - this may be too conservative for some C++ types. > + The last two questions can be solved in the same way as the first > + two questions but this is too conservative. The observation is > + that in some cases we can know which (if any) fields are addressed > + and if those addresses are used in bad ways. This analysis may be > + language specific. In C, arbitrary operations may be applied to > + pointers. However, there is some indication that this may be too > + conservative for some C++ types. > > The pass ipa-type-escape does this analysis for the types whose > instances do not escape across the compilation boundary. > > Historically in GCC, these two problems were combined and a single > - data structure was used to represent the solution to these > + data structure that was used to represent the solution to these > problems. We now have two similar but different data structures, > - The data structure to solve the last two question is similar to the > - first, but does not contain have the fields in it whose address are > - never taken. For types that do escape the compilation unit, the > - data structures will have identical information. > + The data structure to solve the last two questions is similar to > + the first, but does not contain the fields whose address are never > + taken. For types that do escape the compilation unit, the data > + structures will have identical information. > */ > > /* The alias sets assigned to MEMs assist the back-end in determining > -- Richard Biener <rguent...@suse.de> SUSE / SUSE Labs SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746 GF: Jeff Hawn, Jennifer Guild, Felix Imend
