On 9/15/18 2:14 AM, Bernd Edlinger wrote: > On 9/14/18, Martin Sebor wrote: >> As I said above, this happens during the dom walk in the ccp >> pass: >> >> substitute_and_fold_dom_walker walker (CDI_DOMINATORS, this); >> walker.walk (ENTRY_BLOCK_PTR_FOR_FN (cfun)); >> >> The warning is issued during the walker.walk() call as >> strncpy is being folded into memcpy. The prior assignments are >> only propagated later, when the next statement after the strncpy >> call is reached. It happens in >> substitute_and_fold_dom_walker::before_dom_children(). So during >> the strncpy folding we see the next statement as: >> >> MEM[(struct S *)_1].a[n_7] = 0; >> >> After the strncpy call is transformed to memcpy, the assignment >> above is transformed to >> >> MEM[(struct S *)_8].a[3] = 0; >> >> >>> If they're only discovered as copies within the pass where you're trying >>> to issue the diagnostic, then you'd want to see if the pass has any >>> internal structures that tell you about equivalences. >> >> >> I don't know if this is possible. I don't see any APIs in >> tree-ssa-propagate.h that would let me query the internal data >> somehow to find out during folding (when the warning is issued). > > > Well, > > if I see this right, the CCP is doing tree transformations > while from the folding of strncpy the predicate maybe_diag_stxncpy_trunc > is called, and sees inconsistent information, in the tree, > and therefore it issues a warning. > > I understand that walking the references is fragile at least > in this state. > > But why not just prevent warnings when this is called from CCP? > > > Like this? > > Bootstrapped and reg-tested on x86_64-pc-linux-gnu. > Is it OK for trunk? No. That's just hacking around the real problem.
jeff
