On Fri, 21 Nov 2008, Richard Guenther wrote: > On Fri, 21 Nov 2008, Jakub Jelinek wrote: > > > On Fri, Nov 21, 2008 at 08:31:18AM -0500, Diego Novillo wrote: > > > On Fri, Nov 21, 2008 at 06:21, Richard Guenther <[EMAIL PROTECTED]> wrote: > > > > > > > I think the only reasonable thing to do is to rip out the broken > > > > restrict pointer handling completely. > > > > > > > > Any better ideas? > > > > > > I will assume that this program is valid. I am not familiar enough > > > with the restrict definition, but ISTM that if __restrict implies a > > > contract not to make the pointers conflict, then this program is > > > obviously violating it. > > > > At least the second testcase in the PR you opened would be easily fixed if > > we did the same as internal_get_tmp_var does for user VAR_DECLs of restrict > > pointers from their initializers. Guess something similar would need > > to be done during inlining for restrict qualified arguments. > > And for variables used by insertion in PRE and LIM. And maybe in > other places, like the vectorizer cases we hit. > > > For the first testcase, I'm not sure how the compiler is supposed to find > > out what other pointer is a restricted pointer based on, when it doesn't > > have an initializer. > > I'm not sure how to read 6.7.3.1/4 for this case (ok, the "Formal > definition of restrict" is written in a completely confusing manner to > me). If assigning a restrict based pointer to something uninitialized > triggers "If P is assigned the value of a pointer expression E that is > based on another restrict pointer object P2, ... then the behavior is > undefined" and whatever is this about the blocks B and B2 doesn't hold > then the first testcase would be undefined. But I think that this > makes the implementation fragile again as we cannot distinguish > between invalid transformations keeping the chains not intact and > initial undefined code.
Btw, the definition of "based on" in 6.7.3.1 seems to make any pointer P based on another pointer Q if changing Q prior to evaluating the expression initializing P changes the value of P. Thus it looks like a pointer P is "based on" a pointer Q if P is value-dependent on Q which is certainly the case for the first testcase. Richard.
