Add tree-ssa-strlen optimization.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@199006 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 29 insertions, 1 deletions

diff --git a/gcc/tree-ssa-strlen.c b/gcc/tree-ssa-strlen.c
index 5ab37645ec6..c0f9ccd5642 100644
--- a/gcc/tree-ssa-strlen.c
+++ b/gcc/tree-ssa-strlen.c
@@ -1694,7 +1694,8 @@ handle_char_store (gimple_stmt_iterator *gsi)
 	      else
 		{
 		  si->writable = true;
-		  si->dont_invalidate = true;
+		  gsi_next (gsi);
+		  return false;
 		}
 	    }
 	  else
@@ -1717,6 +1718,33 @@ handle_char_store (gimple_stmt_iterator *gsi)
 	    si->endptr = ssaname;
 	  si->dont_invalidate = true;
 	}
+      /* If si->length is non-zero constant, we aren't overwriting '\0',
+	 and if we aren't storing '\0', we know that the length of the
+	 string and any other zero terminated string in memory remains
+	 the same.  In that case we move to the next gimple statement and
+	 return to signal the caller that it shouldn't invalidate anything.  
+
+	 This is benefical for cases like:
+
+	 char p[20];
+	 void foo (char *q)
+	 {
+	   strcpy (p, "foobar");
+	   size_t len = strlen (p);        // This can be optimized into 6
+	   size_t len2 = strlen (q);        // This has to be computed
+	   p[0] = 'X';
+	   size_t len3 = strlen (p);        // This can be optimized into 6
+	   size_t len4 = strlen (q);        // This can be optimized into len2
+	   bar (len, len2, len3, len4);
+        }
+	*/ 
+      else if (si != NULL && si->length != NULL_TREE
+	       && TREE_CODE (si->length) == INTEGER_CST
+	       && integer_nonzerop (gimple_assign_rhs1 (stmt)))
+	{
+	  gsi_next (gsi);
+	  return false;
+	}
     }
   else if (idx == 0 && initializer_zerop (gimple_assign_rhs1 (stmt)))
     {