[arm] Save lr in thumb mode

[Paul Brook <paul at codesourcery dot com>]

We don't check if the link register is clobbered in a thumb function. We make 
lr a fixed reg, then check for specific code sequences that are known to 
clobber LR. However it can also be clobered by inline assembly.

The following example will be miscompiled:

void foo(int a)
{
  asm volatile ("mov lr, %0" :: "r" (a) : "lr");
}

The patch below fixes this by doing the same as we do in arm mode. I'm not 
sure if the lr_save_eliminated dance is actually necessary, but it doesn't do 
any harm.

Tested with cross to arm-none-elf.
Ok?

Paul

2004-05-27  Paul Brook  <paul@codesourcery.com>

	* config/arm/arm.c (thumb_force_lr_save): New function.
	(arm_get_frame_offsets, thumb_unexpanded_epilogue,
	thumb_output_function_prologue): Use it.
	(thumb_expand_prologue): Set lr_save_eliminated.

Index: arm.c
===================================================================
RCS file: /var/cvsroot/gcc-cvs/gcc/gcc/config/arm/arm.c,v
retrieving revision 1.363
diff -u -p -r1.363 arm.c
--- arm.c	25 May 2004 21:43:53 -0000	1.363
+++ arm.c	26 May 2004 22:04:35 -0000
@@ -9960,6 +9960,18 @@ emit_sfm (int base_reg, int count)
 }
 
 
+/* Return true if the current function needs to save/restore LR.  */
+
+static bool
+thumb_force_lr_save (void)
+{
+  return !cfun->machine->lr_save_eliminated
+	 && (!leaf_function_p ()
+	     || thumb_far_jump_used_p ()
+	     || regs_ever_live [LR_REGNUM]);
+}
+
+
 /* Compute the distance from register FROM to register TO.
    These can be the arg pointer (26), the soft frame pointer (25),
    the stack pointer (13) or the hard frame pointer (11).
@@ -10095,8 +10107,7 @@ arm_get_frame_offsets (void)
       for (reg = 0; reg <= LAST_LO_REGNUM; reg ++)
 	if (THUMB_REG_PUSHED_P (reg))
 	  count_regs ++;
-      if (count_regs || ! leaf_function_p ()
-	  || thumb_far_jump_used_p ())
+      if (count_regs || thumb_force_lr_save ())
 	saved += 4 * (count_regs + 1);
       if (TARGET_BACKTRACE)
 	{
@@ -12916,7 +12927,6 @@ thumb_unexpanded_epilogue (void)
   int regno;
   int live_regs_mask = 0;
   int high_regs_pushed = 0;
-  int leaf_function = leaf_function_p ();
   int had_to_push_lr;
   rtx eh_ofs = cfun->machine->eh_epilogue_sp_ofs;
 
@@ -13011,8 +13021,7 @@ thumb_unexpanded_epilogue (void)
 	}
     }
 
-  had_to_push_lr = (live_regs_mask || !leaf_function
-		    || thumb_far_jump_used_p ());
+  had_to_push_lr = (live_regs_mask || thumb_force_lr_save ());
   
   if (TARGET_BACKTRACE
       && ((live_regs_mask & 0xFF) == 0)
@@ -13172,6 +13181,7 @@ thumb_expand_prologue (void)
   HOST_WIDE_INT amount;
   arm_stack_offsets *offsets;
   unsigned long func_type;
+  int regno;
 
   func_type = arm_current_func_type ();
   
@@ -13205,7 +13215,6 @@ thumb_expand_prologue (void)
 	}
       else
 	{
-	  int regno;
 	  rtx reg;
 
 	  /* The stack decrement is too big for an immediate value in a single
@@ -13290,6 +13299,21 @@ thumb_expand_prologue (void)
   
   if (current_function_profile || TARGET_NO_SCHED_PRO)
     emit_insn (gen_blockage ());
+
+  cfun->machine->lr_save_eliminated = !thumb_force_lr_save ();
+  for (regno = 0; regno <= LAST_LO_REGNUM; regno++)
+    {
+      if (THUMB_REG_PUSHED_P (regno))
+        {
+          cfun->machine->lr_save_eliminated = 0;
+          break;
+        }
+    }
+
+  /* If the link register is being kept alive, with the return address in it,
+     then make sure that it does not get reused by the ce2 pass.  */
+  if (cfun->machine->lr_save_eliminated)
+    emit_insn (gen_prologue_use (gen_rtx_REG (SImode, LR_REGNUM)));
 }
 
 void
@@ -13424,7 +13448,7 @@ thumb_output_function_prologue (FILE *f,
     if (THUMB_REG_PUSHED_P (regno))
       live_regs_mask |= 1 << regno;
 
-  if (live_regs_mask || !leaf_function_p () || thumb_far_jump_used_p ())
+  if (live_regs_mask || thumb_force_lr_save ())
     live_regs_mask |= 1 << LR_REGNUM;
 
   if (TARGET_BACKTRACE)