Fix uninitialized register read problem.

* builtins.c (expand_builtin_return_addr): Set
current_function_accesses_prior_frames when count != 0.  Use
frame_pointer_rtx when count == 0.
* function.h (struct function): Add accesses_prior_frames field.
(current_function_accesses_prior_frames): Define.
* reload1.c (init_elim_table): Check
current_function_accesses_prior_frames.
* doc/tm.texi (INITIAL_FRAME_ADDRESS_RTX): Update docs.

From-SVN: r103294

gcc/ChangeLog

+2005-08-19  James E Wilson  <wilson@specifix.com>
+
+	* builtins.c (expand_builtin_return_addr): Set
+	current_function_accesses_prior_frames when count != 0.  Use
+	frame_pointer_rtx when count == 0.
+	* function.h (struct function): Add accesses_prior_frames field.
+	(current_function_accesses_prior_frames): Define.
+	* reload1.c (init_elim_table): Check
+	current_function_accesses_prior_frames.
+	* doc/tm.texi (INITIAL_FRAME_ADDRESS_RTX): Update docs.
+
 2005-08-19  Diego Novillo  <dnovillo@redhat.com>
 
 	* tree-cfgcleanup.c (cleanup_tree_cfg): Fix flowgraph change

gcc/builtins.c

@@ -485,7 +485,22 @@ expand_builtin_return_addr (enum built_in_function fndecl_code, int count)
 #ifdef INITIAL_FRAME_ADDRESS_RTX
   rtx tem = INITIAL_FRAME_ADDRESS_RTX;
 #else
-  rtx tem = hard_frame_pointer_rtx;
+  rtx tem;
+
+  /* For a zero count, we don't care what frame address we return, so frame
+     pointer elimination is OK, and using the soft frame pointer is OK.
+     For a non-zero count, we require a stable offset from the current frame
+     pointer to the previous one, so we must use the hard frame pointer, and
+     we must disable frame pointer elimination.  */
+  if (count == 0)
+    tem = frame_pointer_rtx;
+  else 
+    {
+      tem = hard_frame_pointer_rtx;
+
+      /* Tell reload not to eliminate the frame pointer.  */
+      current_function_accesses_prior_frames = 1;
+    }
 #endif
 
   /* Some machines need special handling before we can access

gcc/doc/tm.texi

@@ -2812,14 +2812,11 @@ machines.  See @file{function.c} for details.
 
 @defmac INITIAL_FRAME_ADDRESS_RTX
 A C expression whose value is RTL representing the address of the initial
- stack frame. This address is passed to @code{RETURN_ADDR_RTX} and 
-@code{DYNAMIC_CHAIN_ADDRESS}.
-If you don't define this macro, the default is to return 
-@code{hard_frame_pointer_rtx}.
-This default is usually correct unless @code{-fomit-frame-pointer} is in 
-effect.
-Define this macro in order to make @code{__builtin_frame_address (0)} and 
-@code{__builtin_return_address (0)} work even in absence of a hard frame pointer.
+stack frame. This address is passed to @code{RETURN_ADDR_RTX} and 
+@code{DYNAMIC_CHAIN_ADDRESS}.  If you don't define this macro, a reasonable
+default value will be used.  Define this macro in order to make frame pointer
+elimination work in the presence of @code{__builtin_frame_address (count)} and 
+@code{__builtin_return_address (count)} for @code{count} not equal to zero.
 @end defmac
 
 @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})

gcc/function.h

@@ -394,6 +394,10 @@ struct function GTY(())
      either as a subroutine or builtin.  */
   unsigned int calls_alloca : 1;
 
+  /* Nonzero if function being compiled called builtin_return_addr or
+     builtin_frame_address with non-zero count.  */
+  unsigned int accesses_prior_frames : 1;
+
   /* Nonzero if the function calls __builtin_eh_return.  */
   unsigned int calls_eh_return : 1;
 
@@ -483,6 +487,7 @@ extern int trampolines_created;
 #define current_function_returns_pointer (cfun->returns_pointer)
 #define current_function_calls_setjmp (cfun->calls_setjmp)
 #define current_function_calls_alloca (cfun->calls_alloca)
+#define current_function_accesses_prior_frames (cfun->accesses_prior_frames)
 #define current_function_calls_eh_return (cfun->calls_eh_return)
 #define current_function_is_thunk (cfun->is_thunk)
 #define current_function_args_info (cfun->args_info)

gcc/reload1.c

@@ -3492,6 +3492,7 @@ init_elim_table (void)
 			     sp-adjusting insns for this case.  */
 			  || (current_function_calls_alloca
 			      && EXIT_IGNORE_STACK)
+			  || current_function_accesses_prior_frames
 			  || FRAME_POINTER_REQUIRED);
 
   num_eliminable = 0;