On Mon, 22 Jan 2024, Jakub Jelinek wrote:
> Hi!
>
> On Mon, Jan 22, 2024 at 11:56:11AM +0100, Richard Biener wrote:
> > > I guess the || total_bytes * BITS_PER_UNIT > HOST_BITS_PER_DOUBLE_INT
> > > conditions make no sense, all we care is whether it fits in the buffer
> > > or not.
> > > But then there is
> > > fold_view_convert_expr
> > > (and other spots) which use
> > > /* We support up to 1024-bit values (for GCN/RISC-V V128QImode). */
> > > unsigned char buffer[128];
> > > or something similar.
> > > Perhaps we could use XALLOCAVEC there instead (or use it only for the
> > > larger sizes and keep the static buffer for the common case).
> >
> > Well, yes. V_C_E folding could do this but then the native_encode_expr
> > API could also allow lazy allocation or so.
>
> native_encode_expr can't reallocate, it has to fill in whatever buffer it
> has been called with, it can be in the middle of something else etc.
>
> The following patch is what I meant, I think having some upper bound is
> desirable so that we don't spend too much time trying to VCE fold 2GB
> structures (after all, the APIs also use int for lengths) and similar and
> passed
> make check-gcc check-g++ -j32 -k GCC_TEST_RUN_EXPENSIVE=1
> RUNTESTFLAGS="GCC_TEST_RUN_EXPENSIVE=1 dg.exp='*bitint* pr112673.c
> builtin-stdc-bit-*.c pr112566-2.c pr112511.c' dg-torture.exp=*bitint*
> dfp.exp=*bitint*"
> (my usual quick test for bitint related changes). Ok for trunk if it passes
> full bootstrap/regtest?
OK.
Thanks,
Richard.
> 2024-01-22 Jakub Jelinek
>
> PR tree-optimization/113462
> * fold-const.cc (native_interpret_int): Don't punt if total_bytes
> is larger than HOST_BITS_PER_DOUBLE_INT / BITS_PER_UNIT.
> (fold_view_convert_expr): Use XALLOCAVEC buffers for types with
> sizes between 129 and 8192 bytes.
>
> --- gcc/fold-const.cc.jj 2024-01-12 10:07:58.202851544 +0100
> +++ gcc/fold-const.cc 2024-01-22 12:09:05.116253393 +0100
> @@ -8773,8 +8773,7 @@ native_interpret_int (tree type, const u
>else
> total_bytes = GET_MODE_SIZE (SCALAR_INT_TYPE_MODE (type));
>
> - if (total_bytes > len
> - || total_bytes * BITS_PER_UNIT > HOST_BITS_PER_DOUBLE_INT)
> + if (total_bytes > len)
> return NULL_TREE;
>
>wide_int result = wi::from_buffer (ptr, total_bytes);
> @@ -9329,9 +9328,10 @@ fold_view_convert_vector_encoding (tree
> static tree
> fold_view_convert_expr (tree type, tree expr)
> {
> - /* We support up to 1024-bit values (for GCN/RISC-V V128QImode). */
>unsigned char buffer[128];
> + unsigned char *buf;
>int len;
> + HOST_WIDE_INT l;
>
>/* Check that the host and target are sane. */
>if (CHAR_BIT != 8 || BITS_PER_UNIT != 8)
> @@ -9341,11 +9341,23 @@ fold_view_convert_expr (tree type, tree
> if (tree res = fold_view_convert_vector_encoding (type, expr))
>return res;
>
> - len = native_encode_expr (expr, buffer, sizeof (buffer));
> + l = int_size_in_bytes (type);
> + if (l > (int) sizeof (buffer)
> + && l <= WIDE_INT_MAX_PRECISION / BITS_PER_UNIT)
> +{
> + buf = XALLOCAVEC (unsigned char, l);
> + len = l;
> +}
> + else
> +{
> + buf = buffer;
> + len = sizeof (buffer);
> +}
> + len = native_encode_expr (expr, buf, len);
>if (len == 0)
> return NULL_TREE;
>
> - return native_interpret_expr (type, buffer, len);
> + return native_interpret_expr (type, buf, len);
> }
>
> /* Build an expression for the address of T. Folds away INDIRECT_REF
>
>
> Jakub
>
>
--
Richard Biener
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
