re PR middle-end/36753 (Forward propagation interacts badly with global register variable)

gcc:
2008-07-17  Paolo Bonzini  <bonzini@gnu.org>

	PR rtl-optimization/36753
	* fwprop.c (use_killed_between): Don't shortcut
	single-definition global registers.

gcc/testsuite:
2008-07-17  Paolo Bonzini  <bonzini@gnu.org>

	PR rtl-optimization/36753
	* gcc.target/i386/pr36753.c: New.

From-SVN: r137913

gcc/ChangeLog

+2008-07-17  Paolo Bonzini  <bonzini@gnu.org>
+
+	PR rtl-optimization/36753
+	* fwprop.c (use_killed_between): Don't shortcut
+	single-definition global registers.
+
 2008-07-16  Jan Hubicka  <jh@suse.cz>
 
 	* cgraph.h (varpool_empty_needed_queue): Declare.

gcc/fwprop.c

@@ -527,10 +527,15 @@ use_killed_between (struct df_ref *use, rtx def_insn, rtx target_insn)
     return true;
 
   /* Check if the reg in USE has only one definition.  We already
-     know that this definition reaches use, or we wouldn't be here.  */
+     know that this definition reaches use, or we wouldn't be here.
+     However, this is invalid for hard registers because if they are
+     live at the beginning of the function it does not mean that we
+     have an uninitialized access.  */
   regno = DF_REF_REGNO (use);
   def = DF_REG_DEF_CHAIN (regno);
-  if (def && (def->next_reg == NULL))
+  if (def
+      && def->next_reg == NULL
+      && regno >= FIRST_PSEUDO_REGISTER)
     return false;
 
   /* Check locally if we are in the same basic block.  */

gcc/testsuite/ChangeLog

+2008-07-17  Paolo Bonzini  <bonzini@gnu.org>
+
+	PR rtl-optimization/36753
+	* gcc.target/i386/pr36753.c: New.
+
 2008-07-17  Tobias Burnus  <burnus@net-b.de>
 
 	PR fortran/36825

gcc/testsuite/gcc.target/i386/pr36753.c

+/* { dg-options "-O2" } */
+/* { dg-do run } */
+
+#if defined __i386__
+#define REG "edi"
+#else
+#define REG "r14"
+#endif
+
+register unsigned long *ds asm(REG);
+
+extern void abort (void);
+
+__attribute__ ((noinline)) void
+test (void)
+{
+  *++ds = 31337;
+}
+
+int
+main ()
+{
+  unsigned long stack[2];
+  stack[0] = 0;
+  stack[1] = 0;
+  ds = stack;
+  test ();
+  if (ds != stack + 1 || *ds != 31337)
+    abort ();
+  return 0;
+}