From 0a0a824808d1dec51004fb5805c1a0ae2a35433f Mon Sep 17 00:00:00 2001
From: Richard Sandiford <richard.sandiford@arm.com>
Date: Tue, 12 Sep 2023 16:08:51 +0100
Subject: [PATCH] aarch64: Rename locals_offset to bytes_above_locals
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locals_offset was described as:

  /* Offset from the base of the frame (incomming SP) to the
     top of the locals area.  This value is always a multiple of
     STACK_BOUNDARY.  */

This is implicitly an “upside down” view of the frame: the incoming
SP is at offset 0, and anything N bytes below the incoming SP is at
offset N (rather than -N).

However, reg_offset instead uses a “right way up” view; that is,
it views offsets in address terms.  Something above X is at a
positive offset from X and something below X is at a negative
offset from X.

Also, even on FRAME_GROWS_DOWNWARD targets like AArch64,
target-independent code views offsets in address terms too:
locals are allocated at negative offsets to virtual_stack_vars.

It seems confusing to have *_offset fields of the same structure
using different polarities like this.  This patch tries to avoid
that by renaming locals_offset to bytes_above_locals.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::locals_offset): Rename to...
	(aarch64_frame::bytes_above_locals): ...this.
	* config/aarch64/aarch64.cc (aarch64_layout_frame)
	(aarch64_initial_elimination_offset): Update accordingly.
---
 gcc/config/aarch64/aarch64.cc | 6 +++---
 gcc/config/aarch64/aarch64.h  | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index d71a042d6112..d4ec352ba98a 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8337,7 +8337,7 @@ aarch64_layout_frame (void)
 			  STACK_BOUNDARY / BITS_PER_UNIT));
   frame.frame_size = saved_regs_and_above + frame.bytes_below_saved_regs;
 
-  frame.locals_offset = frame.saved_varargs_size;
+  frame.bytes_above_locals = frame.saved_varargs_size;
 
   frame.initial_adjust = 0;
   frame.final_adjust = 0;
@@ -12578,13 +12578,13 @@ aarch64_initial_elimination_offset (unsigned from, unsigned to)
 	return frame.hard_fp_offset;
 
       if (from == FRAME_POINTER_REGNUM)
-	return frame.hard_fp_offset - frame.locals_offset;
+	return frame.hard_fp_offset - frame.bytes_above_locals;
     }
 
   if (to == STACK_POINTER_REGNUM)
     {
       if (from == FRAME_POINTER_REGNUM)
-	return frame.frame_size - frame.locals_offset;
+	return frame.frame_size - frame.bytes_above_locals;
     }
 
   return frame.frame_size;
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 94fca4b94716..bf46e6124aa9 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -885,10 +885,10 @@ struct GTY (()) aarch64_frame
      always a multiple of STACK_BOUNDARY.  */
   poly_int64 bytes_below_hard_fp;
 
-  /* Offset from the base of the frame (incomming SP) to the
-     top of the locals area.  This value is always a multiple of
+  /* The number of bytes between the top of the locals area and the top
+     of the frame (the incomming SP).  This value is always a multiple of
      STACK_BOUNDARY.  */
-  poly_int64 locals_offset;
+  poly_int64 bytes_above_locals;
 
   /* Offset from the base of the frame (incomming SP) to the
      hard_frame_pointer.  This value is always a multiple of
-- 
2.43.5