On Wed, Dec 2, 2020 at 5:31 PM Richard Sandiford via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> This is a gcc-10 version of:
>
> Richard Sandiford <richard.sandif...@arm.com> writes:
> > [Sorry, been sitting on this patch for a while and just realised
> > I never sent it.]
> >
> > This is yet another PR caused by constant integer rtxes not storing
> > a mode. We were calling REDUCE_BIT_FIELD on a constant integer that
> > didn't fit in poly_int64, and then tripped the as_a<scalar_int_mode>
> > assert on VOIDmode.
> >
> > AFAICT REDUCE_BIT_FIELD is always passed rtxes that have TYPE_MODE
> > (rather than some other mode) and it just fills in the redundant
> > sign bits of that TYPE_MODE value. So it should be safe to get
> > the mode from the type instead of the rtx. The patch does that
> > and asserts that the modes agree, where information is available.
> >
> > That on its own is enough to fix the bug, but we might as well
> > extend the folding case to all constant integers, not just those
> > that fit poly_int64.
> >
> > Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to trunk
> > and release branches?
>
> The mainline patch ended up causing PR96151, so this patch folds
> in the fix for that. It also avoids some C++11-isms.
>
> Tested on aarch64-linux-gnu, aarch64_be-elf, arm-linux-gnueabihf,
> armeb-elf and x86_64-linux-gnu. OK for GCC 10?
OK.
> (I didn't include PR96151 in the changelog since it's no longer
> a live bug.)
>
> Richard
>
>
> gcc/
> PR middle-end/95694
> * expr.c (expand_expr_real_2): Get the mode from the type rather
> than the rtx, and assert that it is consistent with the mode of
> the rtx (where known). Optimize all constant integers, not just
> those that can be represented in poly_int64.
>
> gcc/testsuite/
> PR middle-end/95694
> * gcc.dg/pr95694.c: New test.
>
> (cherry picked from commit 760df6d296b8fc59796f42dca5eb14012fbfa28b)
> ---
> gcc/expr.c | 19 ++++++++++---------
> gcc/testsuite/gcc.dg/pr95694.c | 23 +++++++++++++++++++++++
> 2 files changed, 33 insertions(+), 9 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/pr95694.c
>
> diff --git a/gcc/expr.c b/gcc/expr.c
> index 6dfee6627a3..991b26f3341 100644
> --- a/gcc/expr.c
> +++ b/gcc/expr.c
> @@ -8560,7 +8560,9 @@ expand_expr_real_2 (sepops ops, rtx target,
> machine_mode tmode,
> reduce_bit_field = (INTEGRAL_TYPE_P (type)
> && !type_has_mode_precision_p (type));
>
> - if (reduce_bit_field && modifier == EXPAND_STACK_PARM)
> + if (reduce_bit_field
> + && (modifier == EXPAND_STACK_PARM
> + || (target && GET_MODE (target) != mode)))
> target = 0;
>
> /* Use subtarget as the target for operand 0 of a binary operation. */
> @@ -11434,26 +11436,25 @@ expand_expr_real_1 (tree exp, rtx target,
> machine_mode tmode,
> static rtx
> reduce_to_bit_field_precision (rtx exp, rtx target, tree type)
> {
> + scalar_int_mode mode = SCALAR_INT_TYPE_MODE (type);
> HOST_WIDE_INT prec = TYPE_PRECISION (type);
> - if (target && GET_MODE (target) != GET_MODE (exp))
> - target = 0;
> - /* For constant values, reduce using build_int_cst_type. */
> - poly_int64 const_exp;
> - if (poly_int_rtx_p (exp, &const_exp))
> + gcc_assert ((GET_MODE (exp) == VOIDmode || GET_MODE (exp) == mode)
> + && (!target || GET_MODE (target) == mode));
> +
> + /* For constant values, reduce using wide_int_to_tree. */
> + if (poly_int_rtx_p (exp))
> {
> - tree t = build_int_cst_type (type, const_exp);
> + tree t = wide_int_to_tree (type, wi::to_poly_wide (exp, mode));
> return expand_expr (t, target, VOIDmode, EXPAND_NORMAL);
> }
> else if (TYPE_UNSIGNED (type))
> {
> - scalar_int_mode mode = as_a <scalar_int_mode> (GET_MODE (exp));
> rtx mask = immed_wide_int_const
> (wi::mask (prec, false, GET_MODE_PRECISION (mode)), mode);
> return expand_and (mode, exp, mask, target);
> }
> else
> {
> - scalar_int_mode mode = as_a <scalar_int_mode> (GET_MODE (exp));
> int count = GET_MODE_PRECISION (mode) - prec;
> exp = expand_shift (LSHIFT_EXPR, mode, exp, count, target, 0);
> return expand_shift (RSHIFT_EXPR, mode, exp, count, target, 0);
> diff --git a/gcc/testsuite/gcc.dg/pr95694.c b/gcc/testsuite/gcc.dg/pr95694.c
> new file mode 100644
> index 00000000000..6f5e1900a02
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr95694.c
> @@ -0,0 +1,23 @@
> +/* PR tree-optimization/68835 */
> +/* { dg-do run { target int128 } } */
> +/* { dg-options "-fno-tree-forwprop -fno-tree-ccp -O1
> -fno-tree-dominator-opts -fno-tree-fre" } */
> +
> +__attribute__((noinline, noclone)) unsigned __int128
> +foo (void)
> +{
> + unsigned __int128 x = (unsigned __int128) 0xffffffffffffffffULL;
> + struct { unsigned __int128 a : 65; } w;
> + w.a = x;
> + w.a += x;
> + return w.a;
> +}
> +
> +int
> +main ()
> +{
> + unsigned __int128 x = foo ();
> + if ((unsigned long long) x != 0xfffffffffffffffeULL
> + || (unsigned long long) (x >> 64) != 1)
> + __builtin_abort ();
> + return 0;
> +}
