On Tue, Jun 21, 2022 at 5:01 AM Jakub Jelinek <[email protected]> wrote:
>
> On Mon, Jun 20, 2022 at 02:42:20PM -0700, Noah Goldstein wrote:
> > This patch allows for strchr(x, c) to the replace with memchr(x, c,
> > strlen(x) + 1) if strlen(x) has already been computed earlier in the
> > tree.
> >
> > Handles PR95821: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95821
> >
> > Since memchr doesn't need to re-find the null terminator it is faster
> > than strchr.
> >
> > bootstrapped and tested on x86_64-linux.
> >
> > PR tree-optimization/95821
>
> This should be indented by a single tab, not two.
Fixed in V3
> >
> > gcc/
> >
> > * tree-ssa-strlen.cc (strlen_pass::handle_builtin_strchr): Emit
> > memchr instead of strchr if strlen already computed.
> >
> > gcc/testsuite/
> >
> > * c-c++-common/pr95821-1.c: New test.
> > * c-c++-common/pr95821-2.c: New test.
> > * c-c++-common/pr95821-3.c: New test.
> > * c-c++-common/pr95821-4.c: New test.
> > * c-c++-common/pr95821-5.c: New test.
> > * c-c++-common/pr95821-6.c: New test.
> > * c-c++-common/pr95821-7.c: New test.
> > * c-c++-common/pr95821-8.c: New test.
> > --- a/gcc/tree-ssa-strlen.cc
> > +++ b/gcc/tree-ssa-strlen.cc
> > @@ -2405,9 +2405,12 @@ strlen_pass::handle_builtin_strlen ()
> > }
> > }
> >
> > -/* Handle a strchr call. If strlen of the first argument is known, replace
> > - the strchr (x, 0) call with the endptr or x + strlen, otherwise remember
> > - that lhs of the call is endptr and strlen of the argument is endptr -
> > x. */
> > +/* Handle a strchr call. If strlen of the first argument is known,
> > + replace the strchr (x, 0) call with the endptr or x + strlen,
> > + otherwise remember that lhs of the call is endptr and strlen of the
> > + argument is endptr - x. If strlen of x is not know but has been
> > + computed earlier in the tree then replace strchr(x, c) to
>
> Still missing space before ( above.
Sorry, fixed that in V3.
>
> > + memchr (x, c, strlen + 1). */
> >
> > void
> > strlen_pass::handle_builtin_strchr ()
> > @@ -2418,8 +2421,12 @@ strlen_pass::handle_builtin_strchr ()
> > if (lhs == NULL_TREE)
> > return;
> >
> > - if (!integer_zerop (gimple_call_arg (stmt, 1)))
> > - return;
> > + tree chr = gimple_call_arg (stmt, 1);
> > + /* strchr only uses the lower char of input so to check if its
> > + strchr (s, zerop) only take into account the lower char. */
> > + bool is_strchr_zerop
> > + = (TREE_CODE (chr) == INTEGER_CST
> > + && integer_zerop (fold_convert (char_type_node, chr)));
>
> The indentation rule is that = should be 2 columns to the right from bool,
> so
>
Fixed in V3.
> bool is_strchr_zerop
> = (TREE_CODE (chr) == INTEGER_CST
> && integer_zerop (fold_convert (char_type_node, chr)));
>
> > + /* If its not strchr (s, zerop) then try and convert to
> > + memchr since strlen has already been computed. */
>
> This comment still has the second line weirdly indented.
Sorry, have emacs with 4-space tabs so things that look right arent
as they seem :/
Fixed in V3 I believe.
>
> > + tree fn = builtin_decl_explicit (BUILT_IN_MEMCHR);
> > +
> > + /* Only need to check length strlen (s) + 1 if chr may be zero.
> > + Otherwise the last chr (which is known to be zero) can never
> > + be a match. NB: We don't need to test if chr is a non-zero
> > + integer const with zero char bits because that is taken into
> > + account with is_strchr_zerop. */
> > + if (!tree_expr_nonzero_p (chr))
>
> The above is unsafe though. tree_expr_nonzero_p (chr) will return true
> if say VRP can prove it is not zero, but because of the implicit
> (char) chr cast done by the function we need something different.
> Say if VRP determines that chr is in [1, INT_MAX] or even just [255, 257]
> it doesn't mean (char) chr won't be 0.
> So, as I've tried to explain in the previous mail, it can be done e.g. with
Added your code in V3. Thanks for the help.
> bool chr_nonzero = false;
> if (TREE_CODE (chr) == INTEGER_CST
> && integer_nonzerop (fold_convert (char_type_node, chr)))
> chr_nonzero = true;
> else if (TREE_CODE (chr) == SSA_NAME
> && CHAR_TYPE_SIZE < INT_TYPE_SIZE)
> {
> value_range r;
> /* Try to determine using ranges if (char) chr must
> be always 0. That is true e.g. if all the subranges
> have the INT_TYPE_SIZE - CHAR_TYPE_SIZE bits
> the same on lower and upper bounds. */
> if (get_range_query (cfun)->range_of_expr (r, chr, stmt)
> && r.kind () == VR_RANGE)
> {
> chr_nonzero = true;
> wide_int mask = wi::mask (CHAR_TYPE_SIZE, true,
> INT_TYPE_SIZE);
> for (int i = 0; i < r.num_pairs (); ++i)
> if ((r.lower_bound (i) & mask)
> != (r.upper_bound (i) & mask))
> {
> chr_nonzero = false;
> break;
> }
> }
> }
> if (!chr_nonzero)
>
> Jakub
>
