re PR tree-optimization/19828 (LIM is pulling out a pure function even though there is something which can modify global memory)

PR tree-optimization/19828
	* tree-ssa-loop-im.c: Add a TODO comment.
	(movement_possibility): Return MOVE_PRESERVE_EXECUTION for calls
	without side-effects.

	* gcc.dg/tree-ssa/loop-7.c: New test.
	* gcc.c-torture/execute/20050218-1.c: New test.

Co-Authored-By: Jakub Jelinek <jakub@redhat.com>

From-SVN: r95275

gcc/ChangeLog

@@ -1,3 +1,11 @@
+2005-02-19  Zdenek Dvorak  <dvorakz@suse.cz>
+	    Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/19828
+	* tree-ssa-loop-im.c: Add a TODO comment.
+	(movement_possibility): Return MOVE_PRESERVE_EXECUTION for calls
+	without side-effects.
+
 2005-02-18  James A. Morrison  <phython@gcc.gnu.org>
 
 	* tree-ssa-ccp.c (widen_bitfield): Pass type to build_int_cst and don't

gcc/testsuite/ChangeLog

@@ -1,3 +1,10 @@
+2005-02-19  Zdenek Dvorak  <dvorakz@suse.cz>
+	    Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/19828
+	* gcc.dg/tree-ssa/loop-7.c: New test.
+	* gcc.c-torture/execute/20050218-1.c: New test.
+
 2005-02-19  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/20043

gcc/testsuite/gcc.c-torture/execute/20050218-1.c

@@ -0,0 +1,30 @@
+/* PR tree-optimization/19828 */
+typedef __SIZE_TYPE__ size_t;
+extern size_t strlen (const char *s);
+extern int strncmp (const char *s1, const char *s2, size_t n);
+extern void abort (void);
+
+const char *a[16] = { "a", "bc", "de", "fgh" };
+
+int
+foo (char *x, const char *y, size_t n)
+{
+  size_t i, j = 0;
+  for (i = 0; i < n; i++)
+    {
+      if (strncmp (x + j, a[i], strlen (a[i])) != 0)
+        return 2;
+      j += strlen (a[i]);
+      if (y)
+        j += strlen (y);
+    }
+  return 0;
+}
+
+int
+main (void)
+{
+  if (foo ("abcde", (const char *) 0, 3) != 0)
+    abort ();
+  return 0;
+}

gcc/testsuite/gcc.dg/tree-ssa/loop-7.c

@@ -0,0 +1,34 @@
+/* PR tree-optimization/19828 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-tree-lim-details" } */
+
+int cst_fun1 (int) __attribute__((__const__));
+int cst_fun2 (int) __attribute__((__const__));
+int pure_fun1 (int) __attribute__((__pure__));
+int pure_fun2 (int) __attribute__((__pure__));
+int foo (void);
+
+int xxx (void)
+{
+  int i, k = foo (), x = 0;
+
+  for (i = 0; i < 100; i++)
+    {
+      x += cst_fun1 (k);
+      x += pure_fun1 (k);
+
+      if (k)
+	{
+	  x += cst_fun2 (k);
+	  x += pure_fun2 (k);
+	}
+    }
+
+  return x;
+}
+
+/* Calls to cst_fun1 and pure_fun1 may be moved out of the loop.
+   Calls to cst_fun2 and pure_fun2 should not be, since calling
+   with k = 0 may be invalid.  */
+
+/* { dg-final { scan-tree-dump-times "Moving statement" 2 "lim" } } */

gcc/tree-ssa-loop-im.c

@@ -38,6 +38,28 @@ Software Foundation, 59 Temple Place - Suite 330, Boston, MA
 #include "tree-pass.h"
 #include "flags.h"
 
+/* TODO:  Support for predicated code motion.  I.e.
+
+   while (1)
+     {
+       if (cond)
+	 {
+	   a = inv;
+	   something;
+	 }
+     }
+
+   Where COND and INV are is invariants, but evaluating INV may trap or be
+   invalid from some other reason if !COND.  This may be transformed to
+
+   if (cond)
+     a = inv;
+   while (1)
+     {
+       if (cond)
+	 something;
+     }  */
+
 /* A type for the list of statements that have to be moved in order to be able
    to hoist an invariant computation.  */
 
@@ -227,6 +249,28 @@ movement_possibility (tree stmt)
       || tree_could_trap_p (rhs))
     return MOVE_PRESERVE_EXECUTION;
 
+  if (get_call_expr_in (stmt))
+    {
+      /* While pure or const call is guaranteed to have no side effects, we
+	 cannot move it arbitrarily.  Consider code like
+
+	 char *s = something ();
+
+	 while (1)
+	   {
+	     if (s)
+	       t = strlen (s);
+	     else
+	       t = 0;
+	   }
+
+	 Here the strlen call cannot be moved out of the loop, even though
+	 s is invariant.  In addition to possibly creating a call with
+	 invalid arguments, moving out a function call that is not executed
+	 may cause performance regressions in case the call is costly and
+	 not executed at all.  */
+      return MOVE_PRESERVE_EXECUTION;
+    }
   return MOVE_POSSIBLE;
 }