re PR rtl-optimization/3508 (builtin memcmp() could be optimised)

        * builtins.c (expand_builtin_memcmp): Optimize memcmp built-in
        when all arguments are known constant.  Fixes PR opt/3508.

        * gcc.c-torture/execute/string-opt-16.c: New testcase.

From-SVN: r48335

gcc/ChangeLog

+2001-12-27  Roger Sayle <roger@eyesopen.com>
+
+	* builtins.c (expand_builtin_memcmp): Optimize memcmp built-in
+	when all arguments are known constant.  Fixes PR opt/3508.
+
 2001-12-27  Kazu Hirata  <kazu@hxi.com>
 
 	* config/h8300/h8300.md (two anonymous patterns): Remove.

gcc/builtins.c

@@ -2252,6 +2252,7 @@ expand_builtin_memcmp (exp, arglist, target, mode)
      enum machine_mode mode;
 {
   tree arg1, arg2, len;
+  const char *p1, *p2;
 
   if (!validate_arglist (arglist,
 		      POINTER_TYPE, POINTER_TYPE, INTEGER_TYPE, VOID_TYPE))
@@ -2271,6 +2272,19 @@ expand_builtin_memcmp (exp, arglist, target, mode)
       return const0_rtx;
     }
 
+  p1 = c_getstr (arg1);
+  p2 = c_getstr (arg2);
+
+  /* If all arguments are constant, and the value of len is not greater
+     than the lengths of arg1 and arg2, evaluate at compile-time.  */
+  if (host_integerp (len, 1) && p1 && p2
+      && compare_tree_int (len, strlen (p1)+1) <= 0
+      && compare_tree_int (len, strlen (p2)+1) <= 0)
+    {
+      const int r = memcmp (p1, p2, tree_low_cst (len, 1));
+      return (r < 0 ? constm1_rtx : (r > 0 ? const1_rtx : const0_rtx));
+    }
+
   /* If len parameter is one, return an expression corresponding to
      (*(const unsigned char*)arg1 - (const unsigned char*)arg2).  */
   if (host_integerp (len, 1) && tree_low_cst (len, 1) == 1)

gcc/testsuite/ChangeLog

+2001-12-27  Roger Sayle <roger@eyesopen.com>
+
+	* gcc.c-torture/execute/string-opt-16.c: New testcase.
+
 2001-12-27  Richard Henderson  <rth@redhat.com>
 
 	* gcc.dg/debug-1.c, gcc.dg/debug-2.c: New.

gcc/testsuite/gcc.c-torture/execute/string-opt-16.c

+/* Copyright (C) 2001  Free Software Foundation.
+
+   Ensure that builtin memcmp operations when all three arguments
+   are constant is optimized and performs correctly.  Taken from
+   PR optimize/3508.
+
+   Written by Roger Sayle, 12/26/2001.  */
+
+extern void abort (void);
+extern void link_error (void);
+
+typedef __SIZE_TYPE__ size_t;
+extern int memcmp (const void *, const void *, size_t);
+
+int
+main (int argc)
+{
+  if (memcmp ("abcd", "efgh", 4) >= 0)
+     link_error ();
+  if (memcmp ("abcd", "abcd", 4) != 0)
+     link_error ();
+  if (memcmp ("efgh", "abcd", 4) <= 0)
+     link_error ();
+  return 0;
+}
+
+#ifdef __OPTIMIZE__
+/* When optimizing, all the above cases should be transformed into
+   something else.  So any remaining calls to the original function
+   should abort.  */
+static int
+memcmp (const void *s1, const void *s2, size_t len)
+{
+  abort ();
+}
+#else
+/* When not optimizing, the above tests may generate references to
+   the function link_error, but should never actually call it.  */
+static void
+link_error ()
+{
+  abort ();
+}
+#endif
+