Hi,
As noted in the PR, GCC C currently has an "undocumented extension" that
silently makes zero-sized static objects into 'extern' as well as
'static’. The warning that would normally be emitted is suppressed without
‘-pedantic’.
This means that they don't get allocated (appearing in the object as an
undefined extern). This is surprising behaviour and can cause assembly-
time fails on at least one target, since such arrays can still be
referenced in the generated code. For most targets, presumably there
would be a link-time fail - also a 'surprising' result for the end user.
Effectively, ISTM we accept wrong code silently without the “-pedantic” flag.
It would seem that if there was a compelling use-case for this, then we
should expose it via a flag, rather than making it the default.
The patch removes the code marking these objects as extern.
Two tests in the test-suite needed change, neither of which appears to
be intentionally testing this "extension". The amended graphite test
generates identical code.
Bootstrapped on x86_64-linux-gnu (all langs), x86_64-apple-darwin.
OK for trunk?
iain
2018-08-14 Iain Sandoe <i...@sandoe.co.uk>
gcc/c:
PR c/19315
* c-decl.c (finish_decl): Don't add the 'extern' storage class to
objects of unknown size.
gcc/testsuite:
PR c/19315
gcc.dg/graphite/pr82451.c: Make array 'a' an extern.
gcc.dg/redecl-10.c: Expect warnings for the static vars with unknown
size.
---
gcc/c/c-decl.c | 8 --------
gcc/testsuite/gcc.dg/graphite/pr82451.c | 2 +-
gcc/testsuite/gcc.dg/redecl-10.c | 4 ++--
3 files changed, 3 insertions(+), 11 deletions(-)
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index ed1dd28cac..da42add073 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -4969,14 +4969,6 @@ finish_decl (tree decl, location_t init_loc, tree init,
case 2:
if (do_default)
error ("array size missing in %q+D", decl);
- /* If a `static' var's size isn't known,
- make it extern as well as static, so it does not get
- allocated.
- If it is not `static', then do not mark extern;
- finish_incomplete_decl will give it a default size
- and it will get allocated. */
- else if (!pedantic && TREE_STATIC (decl) && !TREE_PUBLIC (decl))
- DECL_EXTERNAL (decl) = 1;
break;
case 3:
diff --git a/gcc/testsuite/gcc.dg/graphite/pr82451.c
b/gcc/testsuite/gcc.dg/graphite/pr82451.c
index 802b931fdd..b2c439bb56 100644
--- a/gcc/testsuite/gcc.dg/graphite/pr82451.c
+++ b/gcc/testsuite/gcc.dg/graphite/pr82451.c
@@ -1,7 +1,7 @@
/* { dg-do compile } */
/* { dg-options "-O -floop-parallelize-all" } */
-static int a[];
+extern int a[];
int b[1];
int c;
static void
diff --git a/gcc/testsuite/gcc.dg/redecl-10.c b/gcc/testsuite/gcc.dg/redecl-10.c
index 525961e7e3..0864311f64 100644
--- a/gcc/testsuite/gcc.dg/redecl-10.c
+++ b/gcc/testsuite/gcc.dg/redecl-10.c
@@ -5,7 +5,7 @@
/* { dg-do compile } */
/* { dg-options "-g" } */
-static int w[];
+static int w[]; /* { dg-warning "array 'w' assumed to have one element" } */
void
f (void)
{
@@ -19,7 +19,7 @@ g (void)
extern int x[] = { 3, 4, 5 }; /* { dg-error "has both" } */
}
-static int y[];
+static int y[]; /* { dg-warning "array 'y' assumed to have one element" } */
void
h (void)
{
--
2.17.1
