arm.c (use_return_insn): New argument, SIBLING.

* arm.c (use_return_insn): New argument, SIBLING.  Support returning
with a single instruction if the stack has been decremented by 4
and we have a frame pointer.  Update all callers.
(output_return_instruction): Likewise.
(arm_output_epilogue): Change argument to SIBLING.  Calculate
really_return from the new argument.  Update all callers.
* arm.h (USE_RETURN_INSN): Pass NULL for the sibling.
* arm.md (sibcall_epilogue): Call use_return_insn directly, and
pass the sibling call.
* arm-protos.h (use_return_insn, arm_output_epilogue): Update
prototypes.

From-SVN: r73761

gcc/ChangeLog

@@ -1,3 +1,17 @@
+2003-11-20  Richard Earnshaw  <rearnsha@arm.com>
+
+	* arm.c (use_return_insn): New argument, SIBLING.  Support returning
+	with a single instruction if the stack has been decremented by 4
+	and we have a frame pointer.  Update all callers.
+	(output_return_instruction): Likewise.
+	(arm_output_epilogue): Change argument to SIBLING.  Calculate
+	really_return from the new argument.  Update all callers.
+	* arm.h (USE_RETURN_INSN): Pass NULL for the sibling.
+	* arm.md (sibcall_epilogue): Call use_return_insn directly, and
+	pass the sibling call.
+	* arm-protos.h (use_return_insn, arm_output_epilogue): Update
+	prototypes.
+
 2003-11-20  Joseph S. Myers  <jsm@polyomino.org.uk>
 
 	* Makefile.in (extraclean): Delete.

gcc/config/arm/arm-protos.h

@@ -24,11 +24,11 @@
 #define GCC_ARM_PROTOS_H
 
 extern void arm_override_options (void);
-extern int use_return_insn (int);
+extern int use_return_insn (int, rtx);
 extern int arm_regno_class (int);
 extern void arm_finalize_pic (int);
 extern int arm_volatile_func (void);
-extern const char *arm_output_epilogue (int);
+extern const char *arm_output_epilogue (rtx);
 extern void arm_expand_prologue (void);
 extern HOST_WIDE_INT arm_get_frame_size	(void);
 extern const char *arm_strip_name_encoding (const char *);

gcc/config/arm/arm.c

@@ -1002,14 +1002,17 @@ arm_current_func_type (void)
   return cfun->machine->func_type;
 }
 
-/* Return 1 if it is possible to return using a single instruction.  */
+/* Return 1 if it is possible to return using a single instruction.  
+   If SIBLING is non-null, this is a test for a return before a sibling
+   call.  SIBLING is the call insn, so we can examine its register usage.  */
 
 int
-use_return_insn (int iscond)
+use_return_insn (int iscond, rtx sibling)
 {
   int regno;
   unsigned int func_type;
   unsigned long saved_int_regs;
+  unsigned HOST_WIDE_INT stack_adjust;
 
   /* Never use a return instruction before reload has run.  */
   if (!reload_completed)
@@ -1025,7 +1028,9 @@ use_return_insn (int iscond)
   /* So do interrupt functions that use the frame pointer.  */
   if (IS_INTERRUPT (func_type) && frame_pointer_needed)
     return 0;
-  
+
+  stack_adjust = arm_get_frame_size () + current_function_outgoing_args_size;
+
   /* As do variadic functions.  */
   if (current_function_pretend_args_size
       || cfun->machine->uses_anonymous_args
@@ -1033,12 +1038,51 @@ use_return_insn (int iscond)
       || ARM_FUNC_TYPE (func_type) == ARM_FT_EXCEPTION_HANDLER
       /* Or if the function calls alloca */
       || current_function_calls_alloca
-      /* Or if there is a stack adjustment.  */
+      /* Or if there is a stack adjustment.  However, if the stack pointer
-      || (arm_get_frame_size () + current_function_outgoing_args_size != 0))
+	 is saved on the stack, we can use a pre-incrementing stack load.  */
+      || !(stack_adjust == 0 || (frame_pointer_needed && stack_adjust == 4)))
     return 0;
 
   saved_int_regs = arm_compute_save_reg_mask ();
 
+  /* Unfortunately, the insn
+
+       ldmib sp, {..., sp, ...}
+
+     triggers a bug on most SA-110 based devices, such that the stack
+     pointer won't be correctly restored if the instruction takes a
+     page fault.  We work around this problem by poping r3 along with
+     the other registers, since that is never slower than executing
+     another instruction.  
+
+     We test for !arm_arch5 here, because code for any architecture
+     less than this could potentially be run on one of the buggy
+     chips.  */
+  if (stack_adjust == 4 && !arm_arch5)
+    {
+      /* Validate that r3 is a call-clobbered register (always true in
+	 the default abi) ... */
+      if (!call_used_regs[3])
+	return 0;
+
+      /* ... that it isn't being used for a return value (always true
+	 until we implement return-in-regs), or for a tail-call
+	 argument ... */
+      if (sibling)
+	{
+	  if (GET_CODE (sibling) != CALL_INSN)
+	    abort ();
+
+	  if (find_regno_fusage (sibling, USE, 3))
+	    return 0;
+	}
+
+      /* ... and that there are no call-saved registers in r0-r2
+	 (always true in the default ABI).  */
+      if (saved_int_regs & 0x7)
+	return 0;
+    }
+
   /* Can't be done if interworking with Thumb, and any registers have been
      stacked.  */
   if (TARGET_INTERWORK && saved_int_regs != 0)
@@ -8194,7 +8238,24 @@ output_return_instruction (rtx operand, int really_return, int reverse)
 	     frame_pointer_needed is true, but only if sp already
 	     points to the base of the saved core registers.  */
 	  if (live_regs_mask & (1 << SP_REGNUM))
-	    sprintf (instr, "ldm%sfd\t%%|sp, {", conditional);
+	    {
+	      unsigned HOST_WIDE_INT stack_adjust =
+		arm_get_frame_size () + current_function_outgoing_args_size;
+	      
+	      if (stack_adjust != 0 && stack_adjust != 4)
+		abort ();
+
+	      if (stack_adjust && arm_arch5)
+		sprintf (instr, "ldm%sib\t%%|sp, {", conditional);
+	      else
+		{
+		  /* If we can't use ldmib (SA110 bug), then try to pop r3
+		     instead.  */
+		  if (stack_adjust)
+		    live_regs_mask |= 1 << 3;
+		  sprintf (instr, "ldm%sfd\t%%|sp, {", conditional);
+		}
+	    }
 	  else
 	    sprintf (instr, "ldm%sfd\t%%|sp!, {", conditional);
 
@@ -8401,7 +8462,7 @@ arm_output_function_prologue (FILE *f, HOST_WIDE_INT frame_size)
 }
 
 const char *
-arm_output_epilogue (int really_return)
+arm_output_epilogue (rtx sibling)
 {
   int reg;
   unsigned long saved_regs_mask;
@@ -8414,10 +8475,11 @@ arm_output_epilogue (int really_return)
   FILE * f = asm_out_file;
   rtx eh_ofs = cfun->machine->eh_epilogue_sp_ofs;
   unsigned int lrm_count = 0;
+  int really_return = (sibling == NULL);
 
   /* If we have already generated the return instruction
      then it is futile to generate anything else.  */
-  if (use_return_insn (FALSE) && return_used_this_function)
+  if (use_return_insn (FALSE, sibling) && return_used_this_function)
     return "";
 
   func_type = arm_current_func_type ();
@@ -8730,7 +8792,7 @@ arm_output_function_epilogue (FILE *file ATTRIBUTE_UNUSED,
       /* We need to take into account any stack-frame rounding.  */
       frame_size = arm_get_frame_size ();
 
-      if (use_return_insn (FALSE)
+      if (use_return_insn (FALSE, NULL)
 	  && return_used_this_function
 	  && (frame_size + current_function_outgoing_args_size) != 0
 	  && !frame_pointer_needed)
@@ -10187,7 +10249,7 @@ arm_final_prescan_insn (rtx insn)
 	      /* Fail if a conditional return is undesirable (eg on a
 		 StrongARM), but still allow this if optimizing for size.  */
 	      else if (GET_CODE (scanbody) == RETURN
-		       && !use_return_insn (TRUE)
+		       && !use_return_insn (TRUE, NULL)
 		       && !optimize_size)
 		fail = TRUE;
 	      else if (GET_CODE (scanbody) == RETURN

gcc/config/arm/arm.h

@@ -1870,7 +1870,7 @@ typedef struct
 /* Determine if the epilogue should be output as RTL.
    You should override this if you define FUNCTION_EXTRA_EPILOGUE.  */
 #define USE_RETURN_INSN(ISCOND)				\
-  (TARGET_ARM ? use_return_insn (ISCOND) : 0)
+  (TARGET_ARM ? use_return_insn (ISCOND, NULL) : 0)
 
 /* Definitions for register eliminations.
 

gcc/config/arm/arm.md

@@ -9338,9 +9338,9 @@
               (unspec_volatile [(return)] VUNSPEC_EPILOGUE)])]
   "TARGET_ARM"
   "*
-  if (USE_RETURN_INSN (FALSE))
+  if (use_return_insn (FALSE, next_nonnote_insn (insn)))
     return output_return_instruction (const_true_rtx, FALSE, FALSE);
-  return arm_output_epilogue (FALSE);
+  return arm_output_epilogue (next_nonnote_insn (insn));
   "
 ;; Length is absolute worst case
   [(set_attr "length" "44")
@@ -9356,7 +9356,7 @@
   "TARGET_EITHER"
   "*
   if (TARGET_ARM)
-    return arm_output_epilogue (TRUE);
+    return arm_output_epilogue (NULL);
   else /* TARGET_THUMB */
     return thumb_unexpanded_epilogue ();
   "