[gcc r11-10988] aarch64: Explicitly handle frames with no saved registers

[gcc r11-10988] aarch64: Explicitly handle frames with no saved registers

[Richard Sandiford]

https://gcc.gnu.org/g:5efdcc8ed19d9d9e708a001f5dc695560411496d

commit r11-10988-g5efdcc8ed19d9d9e708a001f5dc695560411496d
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Sep 12 16:19:44 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.c (aarch64_layout_frame): Explicitly
            allocate the frame in one go if there are no saved registers.

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

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 6bc026bd08f9..05e6ae8c0c96 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -7609,9 +7609,11 @@ 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: