2010-06-21  Nathan Sidwell  <nathan@codesourcery.com>

	gcc/
	* gimplify.c (gimplify_modify_expr): When assigning to volatiles,
	copy the src value and return a copy.

	gcc/testsuite/
	* gcc.target/i386/volatile-2.c: New.

Index: gimplify.c
===================================================================
--- gimplify.c	(revision 160876)
+++ gimplify.c	(working copy)
@@ -4467,6 +4467,28 @@
   gcc_assert (TREE_CODE (*expr_p) == MODIFY_EXPR
 	      || TREE_CODE (*expr_p) == INIT_EXPR);
 
+  if (want_value && TREE_THIS_VOLATILE (TREE_TYPE (*to_p)))
+    {
+      /* copy the rhs to a temporary, store the temporary and then
+         return it.  This makes sure we consistently do not re-read a
+         volatile just after storing it.  */
+      tree lhs = *to_p;
+      tree rhs = *from_p;
+      tree nv_type = TYPE_MAIN_VARIANT (TREE_TYPE (lhs));
+      tree tmp = create_tmp_var (nv_type, "modtmp");
+      tree tmp_ass = build2 (MODIFY_EXPR, nv_type, tmp, rhs);
+      tree vol_ass = build2 (MODIFY_EXPR, nv_type, lhs, tmp);
+      
+      recalculate_side_effects (tmp_ass);
+      gimplify_and_add (tmp_ass, pre_p);
+
+      recalculate_side_effects (vol_ass);
+      gimplify_and_add (vol_ass, pre_p);
+
+      *expr_p = tmp;
+      return GS_OK;
+    }
+  
   /* Insert pointer conversions required by the middle-end that are not
      required by the frontend.  This fixes middle-end type checking for
      for example gcc.dg/redecl-6.c.  */
Index: testsuite/gcc.target/i386/volatile-2.c
===================================================================
--- testsuite/gcc.target/i386/volatile-2.c	(revision 0)
+++ testsuite/gcc.target/i386/volatile-2.c	(revision 0)
@@ -0,0 +1,92 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+/* Check volatiles are written, read or not re-read consistently */
+
+
+/* simple assignments */
+
+extern int volatile obj_0;
+void test_0 (int data)
+{
+  /* should not reread obj */
+  /* { dg-final { scan-assembler "movl\[ \t\]\[^,\]+, obj_0" } } */
+  /* { dg-final { scan-assembler-not "movl\[ \t\]obj_0," } } */
+  obj_0 = data;
+}
+
+extern int volatile obj_1;
+int test_1 (int data)
+{
+  /* should not reread obj */
+  /* { dg-final { scan-assembler "movl\[ \t\]\[^,\]+, obj_1" } } */
+  /* { dg-final { scan-assembler-not "movl\[ \t\]obj_1," } } */
+  return obj_1 = data;
+}
+
+extern int volatile obj_2;
+int test_2 (void)
+{
+  /* should not reread obj */
+  /* { dg-final { scan-assembler "movl\[ \t\]\[^,\]+, obj_2" } } */
+  /* { dg-final { scan-assembler-not "movl\[ \t\]obj_2," } } */
+  return obj_2 = 0;
+}
+
+
+/* Assignments in compound exprs */
+
+extern int volatile obj_3;
+int test_3 (int data)
+{
+  /* should not reread obj */
+  /* { dg-final { scan-assembler "movl\[ \t\]\[^,\]+, obj_3" } } */
+  /* { dg-final { scan-assembler-not "movl\[ \t\]obj_3," } } */
+  return (obj_3 = data, 0);
+}
+
+extern int volatile obj_4;
+int test_4 (void)
+{
+  /* should not reread obj */
+  /* { dg-final { scan-assembler "movl\[ \t\]\[^,\]+, obj_4" } } */
+  /* { dg-final { scan-assembler-not "movl\[ \t\]obj_4," } } */
+  return (obj_4 = 0, 0);
+}
+extern int volatile obj_5;
+int test_5 (void)
+{
+  /* should reread obj */
+  /* { dg-final { scan-assembler "movl\[ \t\]\[^,\]+, obj_5" } } */
+  /* { dg-final { scan-assembler "movl\[ \t\]obj_5," } } */
+  return (obj_5 = 0, obj_5);
+}
+
+/* Assignments in conditional exprs */
+
+extern int volatile obj_6;
+void test_6 (int data, int cond)
+{
+  /* should not reread obj */
+  /* { dg-final { scan-assembler "movl\[ \t\]\[^,\]+, obj_6" } } */
+  /* { dg-final { scan-assembler-not "movl\[ \t\]obj_6," } } */
+  cond ? obj_6 = data : 0;
+}
+
+extern int volatile obj_7;
+int test_7 (int data, int cond)
+{
+  /* should not reread obj */
+  /* { dg-final { scan-assembler "movl\[ \t\]\[^,\]+, obj_7" } } */
+  /* { dg-final { scan-assembler-not "movl\[ \t\]obj_7," } } */
+  return cond ? obj_7 = data : 0;
+}
+
+extern int volatile obj_8;
+int test_8 (int cond)
+{
+  /* should not reread obj */
+  /* { dg-final { scan-assembler "movl\[ \t\]\[^,\]+, obj_8" } } */
+  /* { dg-final { scan-assembler-not "movl\[ \t\]obj_8," } } */
+  return cond ? obj_8 = 0 : 0;
+}