On 10/6/20 1:58 PM, Andrew MacLeod via Gcc-patches wrote:
On 10/6/20 1:48 PM, Jakub Jelinek wrote:
On Tue, Oct 06, 2020 at 01:41:54PM -0400, Andrew MacLeod wrote:
On 10/6/20 1:32 PM, Jakub Jelinek via Gcc-patches wrote:
On Tue, Oct 06, 2020 at 10:42:12AM -0600, Martin Sebor wrote:
The manual documents the [0] extension and mentions but discourages
using [1]. Nothing is said about other sizes and the warnings such
as -Warray-bounds have been increasingly complaining about accesses
past the declared constant bound (it won't complain about past-
the-end accesses to a mem[1], but will about those to mem[2]).
It would be nice if existing GCC code could eventually be converted
to avoid relying on the [1] hack. I would hope we would avoid making
use of it in new code (and certainly avoid extending its uses to
other
sizes).
I don't see how we could, because [0] is an extension and GCC needs to
support host compilers that don't support it, and similarly [] is an
extension in C++ and can't be relied on.
Changing say rtl or gimple structs from the way we define them
currently
to say templates dependent on the size of the embedded arrays is I'm
afraid not really possible.
Jakub
Aldy is currently testing this.. I presume this is what you had in
mind?
Yes.
I'm not actually sure if it is best to use struct irange (and why struct
irange rather than just irange?) for the r variable, whether it
shouldn't
be unsigned char * or whatever is best suitable type for placement new.
bah, the struct is a carry over from when it was struct new_ir. doh.
as to the type for placement new, I dunno.
The authorities inform me that void * is preferred.. so.. final spin, in
testing now:
diff --git a/gcc/value-range.h b/gcc/value-range.h
index 7031a823138..02a952bf81f 100644
--- a/gcc/value-range.h
+++ b/gcc/value-range.h
@@ -668,13 +668,12 @@ irange_allocator::allocate (unsigned num_pairs)
if (num_pairs < 2)
num_pairs = 2;
- struct newir {
- irange range;
- tree mem[2];
- };
- size_t nbytes = (sizeof (newir) + sizeof (tree) * 2 * (num_pairs - 1));
- struct newir *r = (newir *) obstack_alloc (&m_obstack, nbytes);
- return new (r) irange (r->mem, num_pairs);
+ size_t nbytes = sizeof (tree) * 2 * num_pairs;
+
+ // Allocate the irnge and required memory for the vector
+ void *r = (irange *) obstack_alloc (&m_obstack, sizeof (irange));
+ tree *mem = (tree *) obstack_alloc (&m_obstack, nbytes);
+ return new (r) irange (mem, num_pairs);
}
inline irange *
