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Re: [PATCH] Fix undefined behavior in the combiner
- From: Richard Biener <rguenther at suse dot de>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Eric Botcazou <ebotcazou at adacore dot com>, Jeff Law <law at redhat dot com>, gcc-patches at gcc dot gnu dot org
- Date: Tue, 25 Mar 2014 10:06:17 +0100 (CET)
- Subject: Re: [PATCH] Fix undefined behavior in the combiner
- Authentication-results: sourceware.org; auth=none
- References: <20140325071248 dot GJ1817 at tucnak dot redhat dot com>
On Tue, 25 Mar 2014, Jakub Jelinek wrote:
> Hi!
>
> simplify_compare_const is sometimes called with two CONST_INTs,
> which means mode is VOIDmode and mode_width is 0, but then it
> happily verifies that mode_width is <= HOST_BITS_PER_WIDE_INT
> and shits stuff by mode_width - 1 (i.e. -1).
> From what I can understand, some optimizations can be still
> performed even when we don't know the mode width, and sometimes
> the caller knows the mode of op0, so it makes sense to pass it down
> to let the function take it into account.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, tested also
> with --with-build-config=bootstrap-ubsan bootstrap.
> Ok for trunk?
Ok.
Thanks,
Richard.
> 2014-03-25 Jakub Jelinek <jakub@redhat.com>
>
> * combine.c (simplify_compare_const): Add MODE argument.
> Handle mode_width 0 as very large mode_width.
> (try_combine, simplify_comparison): Adjust callers.
>
> --- gcc/combine.c.jj 2014-03-03 08:24:33.000000000 +0100
> +++ gcc/combine.c 2014-03-24 11:31:13.390695208 +0100
> @@ -446,7 +446,8 @@ static rtx simplify_shift_const (rtx, en
> int);
> static int recog_for_combine (rtx *, rtx, rtx *);
> static rtx gen_lowpart_for_combine (enum machine_mode, rtx);
> -static enum rtx_code simplify_compare_const (enum rtx_code, rtx, rtx *);
> +static enum rtx_code simplify_compare_const (enum rtx_code, enum machine_mode,
> + rtx, rtx *);
> static enum rtx_code simplify_comparison (enum rtx_code, rtx *, rtx *);
> static void update_table_tick (rtx);
> static void record_value_for_reg (rtx, rtx, rtx);
> @@ -2949,7 +2950,7 @@ try_combine (rtx i3, rtx i2, rtx i1, rtx
> {
> compare_code = orig_compare_code = GET_CODE (*cc_use_loc);
> compare_code = simplify_compare_const (compare_code,
> - op0, &op1);
> + GET_MODE (i2dest), op0, &op1);
> target_canonicalize_comparison (&compare_code, &op0, &op1, 1);
> }
>
> @@ -10817,9 +10818,9 @@ gen_lowpart_for_combine (enum machine_mo
> *POP1 may be updated. */
>
> static enum rtx_code
> -simplify_compare_const (enum rtx_code code, rtx op0, rtx *pop1)
> +simplify_compare_const (enum rtx_code code, enum machine_mode mode,
> + rtx op0, rtx *pop1)
> {
> - enum machine_mode mode = GET_MODE (op0);
> unsigned int mode_width = GET_MODE_PRECISION (mode);
> HOST_WIDE_INT const_op = INTVAL (*pop1);
>
> @@ -10835,7 +10836,7 @@ simplify_compare_const (enum rtx_code co
> if (const_op
> && (code == EQ || code == NE || code == GE || code == GEU
> || code == LT || code == LTU)
> - && mode_width <= HOST_BITS_PER_WIDE_INT
> + && mode_width - 1 < HOST_BITS_PER_WIDE_INT
> && exact_log2 (const_op & GET_MODE_MASK (mode)) >= 0
> && (nonzero_bits (op0, mode)
> == (unsigned HOST_WIDE_INT) (const_op & GET_MODE_MASK (mode))))
> @@ -10882,7 +10883,7 @@ simplify_compare_const (enum rtx_code co
> /* If we are doing a <= 0 comparison on a value known to have
> a zero sign bit, we can replace this with == 0. */
> else if (const_op == 0
> - && mode_width <= HOST_BITS_PER_WIDE_INT
> + && mode_width - 1 < HOST_BITS_PER_WIDE_INT
> && (nonzero_bits (op0, mode)
> & ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)))
> == 0)
> @@ -10911,7 +10912,7 @@ simplify_compare_const (enum rtx_code co
> /* If we are doing a > 0 comparison on a value known to have
> a zero sign bit, we can replace this with != 0. */
> else if (const_op == 0
> - && mode_width <= HOST_BITS_PER_WIDE_INT
> + && mode_width - 1 < HOST_BITS_PER_WIDE_INT
> && (nonzero_bits (op0, mode)
> & ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)))
> == 0)
> @@ -10927,7 +10928,7 @@ simplify_compare_const (enum rtx_code co
> /* ... fall through ... */
> }
> /* (unsigned) < 0x80000000 is equivalent to >= 0. */
> - else if (mode_width <= HOST_BITS_PER_WIDE_INT
> + else if (mode_width - 1 < HOST_BITS_PER_WIDE_INT
> && (unsigned HOST_WIDE_INT) const_op
> == (unsigned HOST_WIDE_INT) 1 << (mode_width - 1))
> {
> @@ -10943,7 +10944,7 @@ simplify_compare_const (enum rtx_code co
> if (const_op == 0)
> code = EQ;
> /* (unsigned) <= 0x7fffffff is equivalent to >= 0. */
> - else if (mode_width <= HOST_BITS_PER_WIDE_INT
> + else if (mode_width - 1 < HOST_BITS_PER_WIDE_INT
> && (unsigned HOST_WIDE_INT) const_op
> == ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)) - 1)
> {
> @@ -10962,7 +10963,7 @@ simplify_compare_const (enum rtx_code co
> }
>
> /* (unsigned) >= 0x80000000 is equivalent to < 0. */
> - else if (mode_width <= HOST_BITS_PER_WIDE_INT
> + else if (mode_width - 1 < HOST_BITS_PER_WIDE_INT
> && (unsigned HOST_WIDE_INT) const_op
> == (unsigned HOST_WIDE_INT) 1 << (mode_width - 1))
> {
> @@ -10978,7 +10979,7 @@ simplify_compare_const (enum rtx_code co
> if (const_op == 0)
> code = NE;
> /* (unsigned) > 0x7fffffff is equivalent to < 0. */
> - else if (mode_width <= HOST_BITS_PER_WIDE_INT
> + else if (mode_width - 1 < HOST_BITS_PER_WIDE_INT
> && (unsigned HOST_WIDE_INT) const_op
> == ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)) - 1)
> {
> @@ -11185,7 +11186,7 @@ simplify_comparison (enum rtx_code code,
>
> /* Try to simplify the compare to constant, possibly changing the
> comparison op, and/or changing op1 to zero. */
> - code = simplify_compare_const (code, op0, &op1);
> + code = simplify_compare_const (code, mode, op0, &op1);
> const_op = INTVAL (op1);
>
> /* Compute some predicates to simplify code below. */
>
> Jakub
>
>
--
Richard Biener <rguenther@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imend"orffer