| Message ID | alpine.LSU.2.20.1712081543220.12252@zhemvz.fhfr.qr |
|---|---|
| State | New |
| Headers | show |
| Series | Fix PR81782 | expand |
On Fri, Dec 08, 2017 at 03:44:03PM +0100, Richard Biener wrote: > > The following fixes spurious uninit warnings for zero-sized arrays. > > Bootstrapped and tested on x86_64-unknown-linux-gnu, applied. > > Richard. > > 2017-12-08 Richard Biener <rguenther@suse.de> > > PR middle-end/81782 > * tree-ssa-uninit.c (warn_uninitialized_vars): Properly > handle accesses outside of zero-sized vars. Is ref.max_size == -1 always guaranteeing no access before offset, only after it? What I fear is e.g. ARRAY_REF with non-constant index with base of MEM_REF with & of a middle of array or something similar? struct S { int x[64]; } foo; MEM_REF[&foo, 40][i] with negative i. Anyway, in this case it is about not printing a warning, so we can give up even if it is theoretically possible. > --- gcc/tree-ssa-uninit.c (revision 255499) > +++ gcc/tree-ssa-uninit.c (working copy) > @@ -296,8 +296,8 @@ warn_uninitialized_vars (bool warn_possi > variable. */ > if (DECL_P (base) > && ref.size != -1 > - && ref.max_size == ref.size > - && (ref.offset + ref.size <= 0 > + && ((ref.max_size == ref.size > + && ref.offset + ref.size <= 0) > || (ref.offset >= 0 > && DECL_SIZE (base) > && TREE_CODE (DECL_SIZE (base)) == INTEGER_CST Jakub
On December 8, 2017 3:58:11 PM GMT+01:00, Jakub Jelinek <jakub@redhat.com> wrote: >On Fri, Dec 08, 2017 at 03:44:03PM +0100, Richard Biener wrote: >> >> The following fixes spurious uninit warnings for zero-sized arrays. >> >> Bootstrapped and tested on x86_64-unknown-linux-gnu, applied. >> >> Richard. >> >> 2017-12-08 Richard Biener <rguenther@suse.de> >> >> PR middle-end/81782 >> * tree-ssa-uninit.c (warn_uninitialized_vars): Properly >> handle accesses outside of zero-sized vars. > >Is ref.max_size == -1 always guaranteeing no access before offset, only >after it? Yes. >What I fear is e.g. ARRAY_REF with non-constant index with base of >MEM_REF with & of a middle of array or something similar? >struct S { int x[64]; } foo; >MEM_REF[&foo, 40][i] with negative i. The array type constraints the access. Invalid accesses invoke undefined behavior. >Anyway, in this case it is about not printing a warning, so we can give >up >even if it is theoretically possible. > >> --- gcc/tree-ssa-uninit.c (revision 255499) >> +++ gcc/tree-ssa-uninit.c (working copy) >> @@ -296,8 +296,8 @@ warn_uninitialized_vars (bool warn_possi >> variable. */ >> if (DECL_P (base) >> && ref.size != -1 >> - && ref.max_size == ref.size >> - && (ref.offset + ref.size <= 0 >> + && ((ref.max_size == ref.size >> + && ref.offset + ref.size <= 0) >> || (ref.offset >= 0 >> && DECL_SIZE (base) >> && TREE_CODE (DECL_SIZE (base)) == INTEGER_CST > > Jakub
Index: gcc/tree-ssa-uninit.c =================================================================== --- gcc/tree-ssa-uninit.c (revision 255499) +++ gcc/tree-ssa-uninit.c (working copy) @@ -296,8 +296,8 @@ warn_uninitialized_vars (bool warn_possi variable. */ if (DECL_P (base) && ref.size != -1 - && ref.max_size == ref.size - && (ref.offset + ref.size <= 0 + && ((ref.max_size == ref.size + && ref.offset + ref.size <= 0) || (ref.offset >= 0 && DECL_SIZE (base) && TREE_CODE (DECL_SIZE (base)) == INTEGER_CST Index: gcc/testsuite/gcc.dg/uninit-pr81782.c =================================================================== --- gcc/testsuite/gcc.dg/uninit-pr81782.c (nonexistent) +++ gcc/testsuite/gcc.dg/uninit-pr81782.c (working copy) @@ -0,0 +1,14 @@ +/* { dg-do compile } */ +/* { dg-options "-Wmaybe-uninitialized" } */ + +int +foo (void) +{ + char empty_array[] = { }; + int i, ret = 0; + + for (i = 0; i < (int) (sizeof (empty_array) / sizeof (empty_array[0])); i++) + ret = empty_array[i]; /* { dg-bogus "uninitialized" } */ + + return ret; +}