Currently, Clang previously diagnosed this code by default:
void f(int a[static 0]);
saying that "static has no effect on zero-length arrays", which was
accurate.
However, static array extents require that the caller of the function
pass a nonnull pointer to an array of *at least* that number of
elements, but it can pass more (see C17 6.7.6.3p6). Given that we allow
zero-sized arrays as a GNU extension and that it's valid to pass more
elements than specified by the static array extent, we now support
zero-sized static array extents with the usual semantics because it can
be useful in cases like:
void my_bzero(char p[static 0], int n);
my_bzero(&c+1, 0); //ok
my_bzero(t+k,n-k); //ok, pattern from actual code
Summary:
Clang -fpic defaults to -fno-semantic-interposition (GCC -fpic defaults
to -fsemantic-interposition).
Users need to specify -fsemantic-interposition to get semantic
interposition behavior.
Semantic interposition is currently a best-effort feature. There may
still be some cases where it is not handled well.
Reviewers: peter.smith, rnk, serge-sans-paille, sfertile, jfb, jdoerfert
Subscribers: dschuff, jyknight, dylanmckay, nemanjai, jvesely, kbarton, fedor.sergeev, asb, rbar, johnrusso, simoncook, sabuasal, niosHD, jrtc27, zzheng, edward-jones, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, arphaman, PkmX, jocewei, jsji, Jim, lenary, s.egerton, pzheng, sameer.abuasal, apazos, luismarques, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D73865
Summary:
Support for this option is needed for building Linux kernel.
This is a very frequently requested feature by kernel developers.
More details : https://lkml.org/lkml/2018/4/4/601
GCC option description for -fdelete-null-pointer-checks:
This Assume that programs cannot safely dereference null pointers,
and that no code or data element resides at address zero.
-fno-delete-null-pointer-checks is the inverse of this implying that
null pointer dereferencing is not undefined.
This feature is implemented in as the function attribute
"null-pointer-is-valid"="true".
This CL only adds the attribute on the function.
It also strips "nonnull" attributes from function arguments but
keeps the related warnings unchanged.
Corresponding LLVM change rL336613 already updated the
optimizations to not treat null pointer dereferencing
as undefined if the attribute is present.
Reviewers: t.p.northover, efriedma, jyknight, chandlerc, rnk, srhines, void, george.burgess.iv
Reviewed By: jyknight
Subscribers: drinkcat, xbolva00, cfe-commits
Differential Revision: https://reviews.llvm.org/D47894
llvm-svn: 337433
In C99, an array parameter declarator might have the form:
direct-declarator '[' 'static' type-qual-list[opt] assign-expr ']'
where the static keyword indicates that the caller will always provide a
pointer to the beginning of an array with at least the number of elements
specified by the assignment expression. For constant sizes, we can use the
new dereferenceable attribute to pass this information to the optimizer. For
VLAs, we don't know the size, but (for addrspace(0)) do know that the pointer
must be nonnull (and so we can use the nonnull attribute).
llvm-svn: 213444
type as written from the ParmVarDecl; it's unclear whether the standard
(C99 6.9.1p10) requires this, but we're following the precedent set by gcc,
and hopefully nobody will ever ask about this again.
PR9559 / <rdar://problem/12621983>.
llvm-svn: 167985
arithmetic on a VLA as 'nsw', per discussion with djg, and
implement pointer arithmetic (other than array accesses) and
pointer subtraction for VLA types.
llvm-svn: 133855
- This is designed to make it obvious that %clang_cc1 is a "test variable"
which is substituted. It is '%clang_cc1' instead of '%clang -cc1' because it
can be useful to redefine what gets run as 'clang -cc1' (for example, to set
a default target).
llvm-svn: 91446
simple test that actually does VLA codegen.
Note that despite the fact that the alloca isn't in the entry block, it
should dominate all uses; this is guaranteed by the restrictions on goto
into VLA scope in C99.
llvm-svn: 61291
Eli Friedman