------- Comment #9 from rguenther at suse dot de 2008-01-16 21:18 ------- Subject: Re: [4.3 Regression] ICE in find_or_generate_expression
On Wed, 16 Jan 2008, amacleod at redhat dot com wrote: > ------- Comment #8 from amacleod at redhat dot com 2008-01-16 20:53 ------- > Created an attachment (id=14951) --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14951&action=view) > --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14951&action=view) > proposed patch for sccvn > > I did some analysis, and then verified with dberlin that I was on the right > track. Thanks! > The root of the problem is a disconnect between SCCVN and PRE. > > The function bar() is a function call which is a constant. SCCVN therefore > puts > it in the tables as a value which can be regenerated by calling bar(). > > PRE in turn looks at the call and notes that it can throw an exception, and > says that it is therefore *not* an expression which can be regenerated. > > Things then fail in find_or_generate_expression() because the expression is in > the table, but PRE is unable to regenerate it. > > In order to fix the problem, we need to make SCCVN and PRE agree whether a > constant function which can throw is an expression which can be regenerated. > > My initial take on that it is not, because the throw could result in some side > effects. > > The decl for bar() is > > extern const unsigned short int **bar (void) __attribute__ ((const)); > > The other question is 'is that really a throwable function?' A const function does not throw. From the docs: "..., and have no effects except the return value." likewise pure functions do not throw. > tree_could_throw_p() currently returns TRUE for bar(). This problem could > also > be fixed by bar() not being a throwable expression. I'm assuming this is well > defined, and currently correct. Yes it is. I think adjusting tree_could_throw_p() is the correct thing to do. Richard. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34648
