Ping: [PATCH][Middle-end][version 3]2nd patch of PR78809 and PR83026

[Qing Zhao <qing dot zhao at oracle dot com>]

Ping for the following patch sent in 3 months ago in the end of GCC8:

https://www.mail-archive.com/gcc-patches@gcc.gnu.org/msg184075.html

I have rebased the patch on the latest GCC9 thunk. 

bootstraped and tested on both X86 and Aarch64. no regression.

the following are more details:

========

Hi, this is the 3rd version for this patch.

the main change compared with 2nd version are:
	1. do not use “compute_objsize” to get the minimum object size per Jeff and Richard’s
comment. Instead, add a new function “determine_min_objsize” for this purpose. This new
function calls “compute_builtin_object_size” to get the minimum objsize, however, due to 
the fact that “compute_builtin_object_size” does nothing for SSA_NAME when optimize > 0 (don’t
know the exactly reason for this), inside “determine_min_objsize”, I have to add  more code
to catch up some simple SSA_NAME cases.

	2. in gimple-fold.c and tree-ssa-structalias.c, add the handling of the new 
BUILT_IN_STRCMP_EQ and BUILT_IN_STRNCMP_EQ in the same places where 
BUILT_IN_STRCMP and BUILT_IN_STRNCMP is checked.

	3. some  format change and comments change per Jeff’s comment. 

let me know if you have any comments.

thanks a lot.

Qing

*********************************

2nd Patch for PR78009 
Patch for PR83026

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78809
Inline strcmp with small constant strings

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83026
missing strlen optimization for strcmp of unequal strings

The design doc for PR78809 is at:
https://www.mail-archive.com/gcc@gcc.gnu.org/msg83822.html

this patch is for the second part of change of PR78809 and PR83026:

B. for strncmp (s1, s2, n) (!)= 0 or strcmp (s1, s2) (!)= 0

B.1. (PR83026) When the lengths of both arguments are constant and
     it's a strcmp:
   * if the lengths are NOT equal, we can safely fold the call
     to a non-zero value.
   * otherwise, do nothing now.

B.2. (PR78809) When the length of one argument is constant, try to replace
the call with a __builtin_str(n)cmp_eq call where possible, i.e:

strncmp (s, STR, C) (!)= 0 in which, s is a pointer to a string, STR is a
string with constant length, C is a constant.
  if (C <= strlen(STR) && sizeof_array(s) > C)
    {
      replace this call with
      __builtin_strncmp_eq (s, STR, C) (!)= 0
    }
  if (C > strlen(STR)
    {
      it can be safely treated as a call to strcmp (s, STR) (!)= 0
      can handled by the following strcmp.
    }

strcmp (s, STR) (!)= 0 in which, s is a pointer to a string, STR is a
string with constant length.
  if  (sizeof_array(s) > strlen(STR))
    {
      replace this call with
      __builtin_strcmp_eq (s, STR, strlen(STR)+1) (!)= 0
    }

later when expanding the new __builtin_str(n)cmp_eq calls, first expand them
as __builtin_memcmp_eq, if the expansion does not succeed, change them back
to call to __builtin_str(n)cmp.

adding test case strcmpopt_2.c and strcmpopt_4.c into gcc.dg for part B of
PR78809 adding test case strcmpopt_3.c into gcc.dg for PR83026

bootstraped and tested on both X86 and Aarch64. no regression.

************************************************
gcc/ChangeLog

+2018-05-21  <qing.zhao@oracle.com>
+	
+	PR middle-end/78809
+	PR middle-end/83026
+	* builtins.c (expand_builtin): Add the handling of BUILT_IN_STRCMP_EQ
+	and BUILT_IN_STRNCMP_EQ.
+	* builtins.def: Add new builtins BUILT_IN_STRCMP_EQ and
+	BUILT_IN_STRNCMP_EQ.
+	* gimple-fold.c (gimple_fold_builtin_string_compare): Add the 
+	handling of BUILTIN_IN_STRCMP_EQ and BUILT_IN_STRNCMP_EQ.
+	(gimple_fold_builtin): Likewise.
+	* tree-ssa-strlen.c (compute_string_length): New function.
+	(determine_min_obsize): New function.
+	(handle_builtin_string_cmp): New function to handle calls to
+	string compare functions.
+	(strlen_optimize_stmt): Add handling to builtin string compare
+	calls. 
+	* tree-ssa-structalias.c (find_func_aliases_for_builtin_call):
+	Add the handling of BUILT_IN_STRCMP_EQ and BUILT_IN_STRNCMP_EQ.
+	* tree.c (build_common_builtin_nodes): Add new defines of
+	BUILT_IN_STRNCMP_EQ and BUILT_IN_STRCMP_EQ.
+

gcc/testsuite/ChangeLog

+2018-05-21  <qing.zhao@oracle.com>
+
+	PR middle-end/78809
+	* gcc.dg/strcmpopt_2.c: New testcase.
+	* gcc.dg/strcmpopt_3.c: New testcase.
+
+	PR middle-end/83026
+	* gcc.dg/strcmpopt_3.c: New testcase.

Attachment: PR78809_B.patch
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