On Sun, Aug 31, 2025 at 4:11 PM Andrew Pinski
<andrew.pin...@oss.qualcomm.com> wrote:
>
> This is a small cleanup by moving the optimization of memcmp to
> memcmp_eq to fab from strlen pass. Since the copy of the other
> part of the memcmp strlen optimization to forwprop, this was the
> only thing left that strlen can do memcmp.
>
> Note this move will cause memcmp_eq to be used for -Os too.
>
> It also removes the optimization from strlen since both are now
> handled elsewhere.
>
> Bootstrapped and tested on x86_64-linux-gnu.
OK.
Note I don't like fab much, at least the parts that are not obviously
instruction selection. Most of it should be part of forwprop or ISEL
or a pre-expand "cleanup" (removal of __builtin_assume_aligned and friends).
So, unless memcmp_eq is unhandled elsewhere and thus we need to
do it late (-> ISEL), I'd rather do it in forwprop.
Richard.
> gcc/ChangeLog:
>
> * tree-ssa-ccp.cc (optimize_memcmp_eq): New function.
> (pass_fold_builtins::execute): Call optimize_memcmp_eq
> for memcmp.
> * tree-ssa-strlen.cc (strlen_pass::handle_builtin_memcmp): Remove.
> (strlen_pass::check_and_optimize_call): Don't call
> handle_builtin_memcmp.
>
> Signed-off-by: Andrew Pinski <andrew.pin...@oss.qualcomm.com>
> ---
> gcc/tree-ssa-ccp.cc | 35 +++++++++++++++++++++++
> gcc/tree-ssa-strlen.cc | 63 ------------------------------------------
> 2 files changed, 35 insertions(+), 63 deletions(-)
>
> diff --git a/gcc/tree-ssa-ccp.cc b/gcc/tree-ssa-ccp.cc
> index f33cc042e9f..f16b37f193e 100644
> --- a/gcc/tree-ssa-ccp.cc
> +++ b/gcc/tree-ssa-ccp.cc
> @@ -155,6 +155,7 @@ along with GCC; see the file COPYING3. If not see
> #include "ipa-prop.h"
> #include "internal-fn.h"
> #include "gimple-range.h"
> +#include "tree-ssa-strlen.h"
>
> /* Possible lattice values. */
> typedef enum
> @@ -4221,6 +4222,36 @@ public:
>
> }; // class pass_fold_builtins
>
> +/* Optimize memcmp STMT into memcmp_eq if it is only used with
> + `== 0` or `!= 0`. */
> +
> +static void
> +optimize_memcmp_eq (gcall *stmt)
> +{
> + /* Make sure memcmp arguments are the correct type. */
> + if (gimple_call_num_args (stmt) != 3)
> + return;
> + tree arg1 = gimple_call_arg (stmt, 0);
> + tree arg2 = gimple_call_arg (stmt, 1);
> + tree len = gimple_call_arg (stmt, 2);
> +
> + if (!POINTER_TYPE_P (TREE_TYPE (arg1)))
> + return;
> + if (!POINTER_TYPE_P (TREE_TYPE (arg2)))
> + return;
> + if (!INTEGRAL_TYPE_P (TREE_TYPE (len)))
> + return;
> + /* The return value of the memcmp has to be used
> + equality comparison to zero. */
> + tree res = gimple_call_lhs (stmt);
> +
> + if (!res || !use_in_zero_equality (res))
> + return;
> +
> + gimple_call_set_fndecl (stmt, builtin_decl_explicit (BUILT_IN_MEMCMP_EQ));
> + update_stmt (stmt);
> +}
> +
> unsigned int
> pass_fold_builtins::execute (function *fun)
> {
> @@ -4285,6 +4316,10 @@ pass_fold_builtins::execute (function *fun)
> gsi_next (&i);
> continue;
>
> + case BUILT_IN_MEMCMP:
> + optimize_memcmp_eq (as_a<gcall*>(stmt));
> + break;
> +
> case BUILT_IN_UNREACHABLE:
> if (optimize_unreachable (i))
> cfg_changed = true;
> diff --git a/gcc/tree-ssa-strlen.cc b/gcc/tree-ssa-strlen.cc
> index c4d64132e53..ade8c7dcadd 100644
> --- a/gcc/tree-ssa-strlen.cc
> +++ b/gcc/tree-ssa-strlen.cc
> @@ -3971,65 +3971,6 @@ use_in_zero_equality (tree res, bool exclusive)
> return first_use;
> }
>
> -/* Handle a call to memcmp. We try to handle small comparisons by
> - converting them to load and compare, and replacing the call to memcmp
> - with a __builtin_memcmp_eq call where possible.
> - return true when call is transformed, return false otherwise. */
> -
> -bool
> -strlen_pass::handle_builtin_memcmp ()
> -{
> - gcall *stmt = as_a <gcall *> (gsi_stmt (m_gsi));
> - tree res = gimple_call_lhs (stmt);
> -
> - if (!res || !use_in_zero_equality (res))
> - return false;
> -
> - tree arg1 = gimple_call_arg (stmt, 0);
> - tree arg2 = gimple_call_arg (stmt, 1);
> - tree len = gimple_call_arg (stmt, 2);
> - unsigned HOST_WIDE_INT leni;
> -
> - if (tree_fits_uhwi_p (len)
> - && (leni = tree_to_uhwi (len)) <= GET_MODE_SIZE (word_mode)
> - && pow2p_hwi (leni))
> - {
> - leni *= CHAR_TYPE_SIZE;
> - unsigned align1 = get_pointer_alignment (arg1);
> - unsigned align2 = get_pointer_alignment (arg2);
> - unsigned align = MIN (align1, align2);
> - scalar_int_mode mode;
> - if (int_mode_for_size (leni, 1).exists (&mode)
> - && (align >= leni || !targetm.slow_unaligned_access (mode, align)))
> - {
> - location_t loc = gimple_location (stmt);
> - tree type, off;
> - type = build_nonstandard_integer_type (leni, 1);
> - gcc_assert (known_eq (GET_MODE_BITSIZE (TYPE_MODE (type)), leni));
> - tree ptrtype = build_pointer_type_for_mode (char_type_node,
> - ptr_mode, true);
> - off = build_int_cst (ptrtype, 0);
> - arg1 = build2_loc (loc, MEM_REF, type, arg1, off);
> - arg2 = build2_loc (loc, MEM_REF, type, arg2, off);
> - tree tem1 = fold_const_aggregate_ref (arg1);
> - if (tem1)
> - arg1 = tem1;
> - tree tem2 = fold_const_aggregate_ref (arg2);
> - if (tem2)
> - arg2 = tem2;
> - res = fold_convert_loc (loc, TREE_TYPE (res),
> - fold_build2_loc (loc, NE_EXPR,
> - boolean_type_node,
> - arg1, arg2));
> - gimplify_and_update_call_from_tree (&m_gsi, res);
> - return true;
> - }
> - }
> -
> - gimple_call_set_fndecl (stmt, builtin_decl_explicit (BUILT_IN_MEMCMP_EQ));
> - return true;
> -}
> -
> /* Given strinfo IDX for ARG, sets LENRNG[] to the range of lengths
> of the string(s) referenced by ARG if it can be determined.
> If the length cannot be determined, sets *SIZE to the size of
> @@ -5520,10 +5461,6 @@ strlen_pass::check_and_optimize_call (bool *zero_write)
> if (handle_builtin_memset (zero_write))
> return false;
> break;
> - case BUILT_IN_MEMCMP:
> - if (handle_builtin_memcmp ())
> - return false;
> - break;
> case BUILT_IN_STRCMP:
> case BUILT_IN_STRNCMP:
> if (handle_builtin_string_cmp ())
> --
> 2.43.0
>
