Re: [PATCH v1] tree-optimization/95821 - Convert strlen + strchr to memchr

[Jakub Jelinek <jakub@redhat.com>]

On Mon, Jun 20, 2022 at 09:35:36AM -0700, Noah Goldstein via Gcc-patches 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.

Do you have a GCC Copyright assignment on file, or do you want to submit
this under DCO ( https://gcc.gnu.org/dco.html )?  If the latter, there
should be a Signed-off-by: line, both in the mail and later commit.
> 
> bootstrapped and tested on x86_64-linux.
> 
> gcc/
> 

As it fixes a GCC bugzilla bug, the ChangeLog entry should start with
	PR tree-optimization/95821
line.
>     * tree-ssa-strlen.cc: Emit memchr instead of strchr if strlen
>      already computed.

All the indented lines in ChangeLog should be indented by tab.
You are modifying strlen_pass::handle_builtin_strchr function, so after
tree-ssa-strlen.cc there should be that function name in parens:
	* tree-ssa-strlen.cc (strlen_pass::handle_builtin_strchr): Emit
	memchr ...

> 
> gcc/testsuite/
> 
>     * c-c++-common/pr95821-1.c
>     * c-c++-common/pr95821-2.c
>     * c-c++-common/pr95821-3.c
>     * c-c++-common/pr95821-4.c
>     * c-c++-common/pr95821-5.c
>     * c-c++-common/pr95821-6.c

All the above lines should end with ": New test." after .c

> --- a/gcc/tree-ssa-strlen.cc
> +++ b/gcc/tree-ssa-strlen.cc

How does the patch relate to the one that H.J. attached in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95821#c4 ?

> @@ -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
> +   memchr(x, c, strlen + 1).  */

Space before ( even in comments.



>  void
>  strlen_pass::handle_builtin_strchr ()
> @@ -2418,8 +2421,8 @@ 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);
> +  bool is_strchr_zerop = integer_zerop (chr);
>  
>    tree src = gimple_call_arg (stmt, 0);
>  
> @@ -2452,32 +2455,56 @@ strlen_pass::handle_builtin_strchr ()
>  	      fprintf (dump_file, "Optimizing: ");
>  	      print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
>  	    }
> -	  if (si != NULL && si->endptr != NULL_TREE)
> +	  if (!is_strchr_zerop)
>  	    {
> -	      rhs = unshare_expr (si->endptr);
> -	      if (!useless_type_conversion_p (TREE_TYPE (lhs),
> -					      TREE_TYPE (rhs)))
> -		rhs = fold_convert_loc (loc, TREE_TYPE (lhs), rhs);
> +	      /* If its not strchr(s, zerop) then try and convert to
> +		       memchr if strlen has already been computed.  */

Again, space before (.  The second line is weirdly formatted, should
be indented below If.

> +	      tree fn = builtin_decl_explicit (BUILT_IN_MEMCHR);
> +	      tree one = build_int_cst (TREE_TYPE (rhs), 1);
> +	      rhs = fold_build2_loc (loc, PLUS_EXPR, TREE_TYPE (rhs),
> +				     unshare_expr (rhs), one);
> +	      tree size = make_ssa_name (TREE_TYPE (rhs));
> +	      gassign *size_stmt = gimple_build_assign (size, rhs);
> +	      gsi_insert_before (&m_gsi, size_stmt, GSI_SAME_STMT);
> +	      rhs = size;
> +	      if (!update_gimple_call (&m_gsi, fn, 3, src, chr, rhs))
> +		return;

I think we should differentiate more.  If integer_nonzerop (chr)
or perhaps better tree_expr_nonzero_p (chr), then it is better
to optimize t = strlen (x); ... p = strchr (x, c); to
t = strlen (x); ... p = memchr (x, c, t);
the t + 1 is only needed if c might be zero.

> +	  /* Don't update strlen of lhs if search-char was non-zero.  */

Wasn't known to be zero is the right thing.

	Jakub