gcc/aarch64-Rename-locals_offset-to-bytes_above_locals.patch

From e628f34ef3a7db3a75aa146b3e75099a9c431d20 Mon Sep 17 00:00:00 2001
From: Richard Sandiford <richard.sandiford@arm.com>
Date: Tue, 27 Jun 2023 11:25:40 +0100
Subject: [PATCH] aarch64: Rename locals_offset to bytes_above_locals
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit

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.c (aarch64_layout_frame)
	(aarch64_initial_elimination_offset): Update accordingly.
---
 gcc/config/aarch64/aarch64.c | 12 +++++++-----
 gcc/config/aarch64/aarch64.h |  6 +++---
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 12df8bb783c..27dd3b7a62b 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -2890,7 +2890,8 @@ aarch64_layout_frame (void)
 		+ cfun->machine->frame.bytes_below_hard_fp,
 		STACK_BOUNDARY / BITS_PER_UNIT);
 
-  cfun->machine->frame.locals_offset = cfun->machine->frame.saved_varargs_size;
+  cfun->machine->frame.bytes_above_locals
+    = cfun->machine->frame.saved_varargs_size;
 
   cfun->machine->frame.initial_adjust = 0;
   cfun->machine->frame.final_adjust = 0;
@@ -2951,7 +2952,8 @@ aarch64_layout_frame (void)
       cfun->machine->frame.bytes_below_hard_fp
 	= cfun->machine->frame.final_adjust;
       cfun->machine->frame.hard_fp_offset = cfun->machine->frame.callee_adjust;
-      cfun->machine->frame.locals_offset = cfun->machine->frame.hard_fp_offset;
+      cfun->machine->frame.bytes_above_locals
+	= cfun->machine->frame.hard_fp_offset;
     }
   else
     {
@@ -5653,14 +5655,14 @@ aarch64_initial_elimination_offset (unsigned from, unsigned to)
 
       if (from == FRAME_POINTER_REGNUM)
 	return cfun->machine->frame.hard_fp_offset
-	       - cfun->machine->frame.locals_offset;
+	       - cfun->machine->frame.bytes_above_locals;
     }
 
   if (to == STACK_POINTER_REGNUM)
     {
       if (from == FRAME_POINTER_REGNUM)
-	  return cfun->machine->frame.frame_size
-		 - cfun->machine->frame.locals_offset;
+	return cfun->machine->frame.frame_size
+	       - cfun->machine->frame.bytes_above_locals;
     }
 
   return cfun->machine->frame.frame_size;
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 6dc6ef2b989..79af237ada6 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -565,10 +565,10 @@ struct GTY (()) aarch64_frame
      always a multiple of STACK_BOUNDARY.  */
   HOST_WIDE_INT 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.  */
-  HOST_WIDE_INT locals_offset;
+  HOST_WIDE_INT bytes_above_locals;
 
   /* Offset from the base of the frame (incomming SP) to the
      hard_frame_pointer.  This value is always a multiple of
-- 
2.39.3