optimize memmove

2 files changed, 23 insertions, 7 deletions

diff --git a/src/library.js b/src/library.js
index 61ef90fd..03dc5cbd 100644
--- a/src/library.js
+++ b/src/library.js
@@ -3696,14 +3696,17 @@ LibraryManager.library = {
   llvm_memcpy_p0i8_p0i8_i32: 'memcpy',
   llvm_memcpy_p0i8_p0i8_i64: 'memcpy',
 
-  memmove__deps: ['memcpy'],
   memmove: function(dest, src, num, idunno) {
-    // not optimized!
-    if (num === 0) return; // will confuse malloc if 0
-    var tmp = _malloc(num);
-    _memcpy(tmp, src, num);
-    _memcpy(dest, tmp, num);
-    _free(tmp);
+    if (src < dest && dest < src + num) {
+      // Copy backwards in a safe manner
+      src += num;
+      dest += num;
+      while (num--) {
+        {{{ makeSetValue('--dest', '0', makeGetValue('--src', '0', 'i8'), 'i8') }}};
+      }
+    } else {
+      {{{ makeCopyValues('dest', 'src', 'num', 'null') }}};
+    }
   },
   llvm_memmove_i32: 'memmove',
   llvm_memmove_i64: 'memmove',
diff --git a/tests/runner.py b/tests/runner.py
index 5c2f5e13..ca3fe473 100644
--- a/tests/runner.py
+++ b/tests/runner.py
@@ -2272,6 +2272,19 @@ def process(filename):
           '''
         self.do_run(src)
 
+    def test_memmove(self):
+      src = '''
+        #include <stdio.h>
+        #include <string.h>
+        int main() {
+          char str[] = "memmove can be very useful....!";
+          memmove (str+20, str+15, 11);
+          puts(str);
+          return 0;
+        }
+      '''
+      self.do_run(src)
+
     def test_bsearch(self):
       if Settings.QUANTUM_SIZE == 1: return self.skip('Test cannot work with q1')