flow.c (insn_dead_p): A clobber of a dead hard register is a dead insn after reload.

	* flow.c (insn_dead_p): A clobber of a dead hard register is a
	dead insn after reload.

From-SVN: r77674

gcc/ChangeLog

+2004-02-11  Richard Henderson  <rth@redhat.com>
+
+	* flow.c (insn_dead_p): A clobber of a dead hard register is a
+	dead insn after reload.
+
 2004-02-11  Ulrich Weigand  <uweigand@de.ibm.com>
 
 	* tree.h (frame_base_decl): Add GTY marker.

gcc/flow.c

@@ -2267,14 +2267,22 @@ insn_dead_p (struct propagate_block_info *pbi, rtx x, int call_ok,
     }
 
   /* A CLOBBER of a pseudo-register that is dead serves no purpose.  That
-     is not necessarily true for hard registers.  */
-  else if (code == CLOBBER && GET_CODE (XEXP (x, 0)) == REG
-	   && REGNO (XEXP (x, 0)) >= FIRST_PSEUDO_REGISTER
-	   && ! REGNO_REG_SET_P (pbi->reg_live, REGNO (XEXP (x, 0))))
-    return 1;
-
-  /* We do not check other CLOBBER or USE here.  An insn consisting of just
-     a CLOBBER or just a USE should not be deleted.  */
+     is not necessarily true for hard registers until after reload.  */
+  else if (code == CLOBBER)
+    {
+      if (GET_CODE (XEXP (x, 0)) == REG
+	  && (REGNO (XEXP (x, 0)) >= FIRST_PSEUDO_REGISTER
+	      || reload_completed)
+	  && ! REGNO_REG_SET_P (pbi->reg_live, REGNO (XEXP (x, 0))))
+	return 1;
+    }
+
+  /* ??? A base USE is a historical relic.  It ought not be needed anymore.
+     Instances where it is still used are either (1) temporary and the USE
+     escaped the pass, (2) cruft and the USE need not be emitted anymore,
+     or (3) hiding bugs elsewhere that are not properly representing data
+     flow.  */
+
   return 0;
 }