re PR rtl-optimization/11381 (volatile memory access optimized away)

	PR optimization/11381
	* simplify-rtx.c (simplify_relational_operation): Check that
	two equal operands have no side-effects before simplifying
	the comparison.

From-SVN: r68869

gcc/ChangeLog

+2003-07-03  Eric Botcazou  <ebotcazou@libertysurf.fr>
+
+	PR optimization/11381
+	* simplify-rtx.c (simplify_relational_operation): Check that
+	two equal operands have no side-effects before simplifying
+	the comparison.
+
 2003-07-02  Jeff Law  <law@redhat.com>
 
 	* expr.c (do_store_flag): Remove special case folding for

gcc/simplify-rtx.c

@@ -2220,8 +2220,10 @@ simplify_relational_operation (code, mode, op0, op1)
     return const0_rtx;
 
   /* For modes without NaNs, if the two operands are equal, we know the
-     result.  */
-  if (!HONOR_NANS (GET_MODE (trueop0)) && rtx_equal_p (trueop0, trueop1))
+     result except if they have side-effects.  */
+  if (! HONOR_NANS (GET_MODE (trueop0))
+      && rtx_equal_p (trueop0, trueop1)
+      && ! side_effects_p (trueop0))
     equal = 1, op0lt = 0, op0ltu = 0, op1lt = 0, op1ltu = 0;
 
   /* If the operands are floating-point constants, see if we can fold

gcc/testsuite/ChangeLog

+2003-07-03  Eric Botcazou  <ebotcazou@libertysurf.fr>
+
+	* gcc.dg/i386-volatile-1.c: New test.
+
 2003-07-02  Nathan Sidwell  <nathan@codesourcery.com>
 
 	PR c++/11072

gcc/testsuite/gcc.dg/i386-volatile-1.c

+/* PR optimization/11381 */
+/* Originator: <tobias@ringstrom.mine.nu> */
+/* { dg-do compile { target i?86-*-* } } */
+/* { dg-options "-O" } */
+
+/* Verify that the comparison is not optimized away. */
+
+void foo(volatile unsigned int *vaddr)
+{
+  while (*vaddr != *vaddr)
+    ;
+}
+
+/* { dg-final { scan-assembler "cmp" } } */