On Tue, Jul 7, 2020 at 9:20 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> [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?
OK.
Thanks,
Richard.
> 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.
> ---
> gcc/expr.c | 15 ++++++++-------
> gcc/testsuite/gcc.dg/pr95694.c | 23 +++++++++++++++++++++++
> 2 files changed, 31 insertions(+), 7 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/pr95694.c
>
> diff --git a/gcc/expr.c b/gcc/expr.c
> index 3c68b0d754c..715edae819a 100644
> --- a/gcc/expr.c
> +++ b/gcc/expr.c
> @@ -11525,26 +11525,27 @@ 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))
> + gcc_assert (GET_MODE (exp) == VOIDmode || GET_MODE (exp) == mode);
> + if (target && GET_MODE (target) != mode)
> target = 0;
> - /* For constant values, reduce using build_int_cst_type. */
> - poly_int64 const_exp;
> - if (poly_int_rtx_p (exp, &const_exp))
> +
> + /* For constant values, reduce using wide_int_to_tree. */
> + if (poly_int_rtx_p (exp))
> {
> - tree t = build_int_cst_type (type, const_exp);
> + auto value = wi::to_poly_wide (exp, mode);
> + tree t = wide_int_to_tree (type, value);
> 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;
> +}
