aarch64: Explicitly handle frames with no saved registers

If a frame has no saved registers, it can be allocated in one go.
There is no need to treat the areas below and above the saved
registers as separate.

And if we allocate the frame in one go, it should be allocated
as the initial_adjust rather than the final_adjust.  This allows the
frame size to grow to guard_size - guard_used_by_caller before a stack
probe is needed.  (A frame with no register saves is necessarily a
leaf frame.)

This is a no-op as thing stand, since a leaf function will have
no outgoing arguments, and so all the frame will be above where
the saved registers normally go.

gcc/
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Explicitly
	allocate the frame in one go if there are no saved registers.

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 9fb9462369361728916e55d14f84678d4d8eabf2..34d0ccc9a67706297847fe25b05fa79350c72a71 100644 (file)
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8678,9 +8678,11 @@ aarch64_layout_frame (void)
 
   HOST_WIDE_INT const_size, const_outgoing_args_size, const_fp_offset;
   HOST_WIDE_INT const_saved_regs_size;
-  if (frame.frame_size.is_constant (&const_size)
-      && const_size < max_push_offset
-      && known_eq (frame.hard_fp_offset, const_size))
+  if (known_eq (frame.saved_regs_size, 0))
+    frame.initial_adjust = frame.frame_size;
+  else if (frame.frame_size.is_constant (&const_size)
+          && const_size < max_push_offset
+          && known_eq (frame.hard_fp_offset, const_size))
     {
       /* Simple, small frame with no outgoing arguments: