Optimize strchr (s, 0) to s + strlen (s).

Optimize strchr (s, 0) to s + strlen (s).

Optimize strchr (s, 0) to s + strlen (s).  strchr (s, 0) appears a common
idiom for finding the end of a string, however it is not a very efficient
way of doing so.  Strlen is a much simpler operation which is significantly
faster (eg. on x86 strlen is 50% faster for strings of 8 bytes and about
twice as fast as strchr on strings of 1KB).

    gcc/
	* gimple-fold.c (gimple_fold_builtin_strchr):
	New function to optimize strchr (s, 0) to strlen.
	(gimple_fold_builtin): Add BUILT_IN_STRCHR case.

    testsuite/
	* gcc.dg/strlenopt-20.c: Update test.
	* gcc.dg/strlenopt-21.c: Likewise.
	* gcc.dg/strlenopt-22.c: Likewise.
	* gcc.dg/strlenopt-22g.c: Likewise.
	* gcc.dg/strlenopt-26.c: Likewise.
	* gcc.dg/strlenopt-5.c: Likewise.
	* gcc.dg/strlenopt-7.c: Likewise.
	* gcc.dg/strlenopt-9.c: Likewise.

From-SVN: r240568