[gcc r12-9857] aarch64: Explicitly handle frames with no saved registers

[Richard Sandiford]

https://gcc.gnu.org/g:03d5e89e7f3be53fd7142556e8e0a2774c653dca

commit r12-9857-g03d5e89e7f3be53fd7142556e8e0a2774c653dca
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Sep 12 16:08:49 2023 +0100

    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:
---
 gcc/config/aarch64/aarch64.cc | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 79253322fd7c..e1f21230c15e 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8378,9 +8378,11 @@ 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: