On September 17, 2018 7:24:16 PM GMT+02:00, Jeff Law <l...@redhat.com> wrote: >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.
The real problem is emitting diagnostics from folding code. Richard. > >jeff
