From 187861af7c51db9eddc6f954b589c121b210fc74 Mon Sep 17 00:00:00 2001
From: Richard Sandiford <richard.sandiford@arm.com>
Date: Tue, 12 Sep 2023 16:08:50 +0100
Subject: [PATCH] aarch64: Tweak aarch64_save/restore_callee_saves

aarch64_save_callee_saves and aarch64_restore_callee_saves took
a parameter called start_offset that gives the offset of the
bottom of the saved register area from the current stack pointer.
However, it's more convenient for later patches if we use the
bottom of the entire frame as the reference point, rather than
the bottom of the saved registers.

Doing that removes the need for the callee_offset field.
Other than that, this is not a win on its own.  It only really
makes sense in combination with the follow-on patches.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::callee_offset): Delete.
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Remove
	callee_offset handling.
	(aarch64_save_callee_saves): Replace the start_offset parameter
	with a bytes_below_sp parameter.
	(aarch64_restore_callee_saves): Likewise.
	(aarch64_expand_prologue): Update accordingly.
	(aarch64_expand_epilogue): Likewise.
---
 gcc/config/aarch64/aarch64.cc | 56 +++++++++++++++++------------------
 gcc/config/aarch64/aarch64.h  |  4 ---
 2 files changed, 28 insertions(+), 32 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index c7d84245fbfc..e79551af41df 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8343,7 +8343,6 @@ aarch64_layout_frame (void)
   frame.final_adjust = 0;
   frame.callee_adjust = 0;
   frame.sve_callee_adjust = 0;
-  frame.callee_offset = 0;
 
   frame.wb_pop_candidate1 = frame.wb_push_candidate1;
   frame.wb_pop_candidate2 = frame.wb_push_candidate2;
@@ -8411,7 +8410,6 @@ aarch64_layout_frame (void)
 	 stp reg1, reg2, [sp, bytes_below_saved_regs]
 	 stp reg3, reg4, [sp, bytes_below_saved_regs + 16]  */
       frame.initial_adjust = frame.frame_size;
-      frame.callee_offset = const_below_saved_regs;
     }
   else if (saves_below_hard_fp_p
 	   && known_eq (frame.saved_regs_size,
@@ -8758,12 +8756,13 @@ aarch64_add_cfa_expression (rtx_insn *insn, rtx reg,
 }
 
 /* Emit code to save the callee-saved registers from register number START
-   to LIMIT to the stack at the location starting at offset START_OFFSET,
-   skipping any write-back candidates if SKIP_WB is true.  HARD_FP_VALID_P
-   is true if the hard frame pointer has been set up.  */
+   to LIMIT to the stack.  The stack pointer is currently BYTES_BELOW_SP
+   bytes above the bottom of the static frame.  Skip any write-back
+   candidates if SKIP_WB is true.  HARD_FP_VALID_P is true if the hard
+   frame pointer has been set up.  */
 
 static void
-aarch64_save_callee_saves (poly_int64 start_offset,
+aarch64_save_callee_saves (poly_int64 bytes_below_sp,
 			   unsigned start, unsigned limit, bool skip_wb,
 			   bool hard_fp_valid_p)
 {
@@ -8791,7 +8790,9 @@ aarch64_save_callee_saves (poly_int64 start_offset,
 
       machine_mode mode = aarch64_reg_save_mode (regno);
       reg = gen_rtx_REG (mode, regno);
-      offset = start_offset + frame.reg_offset[regno];
+      offset = (frame.reg_offset[regno]
+		+ frame.bytes_below_saved_regs
+		- bytes_below_sp);
       rtx base_rtx = stack_pointer_rtx;
       poly_int64 sp_offset = offset;
 
@@ -8802,9 +8803,7 @@ aarch64_save_callee_saves (poly_int64 start_offset,
       else if (GP_REGNUM_P (regno)
 	       && (!offset.is_constant (&const_offset) || const_offset >= 512))
 	{
-	  gcc_assert (known_eq (start_offset, 0));
-	  poly_int64 fp_offset
-	    = frame.below_hard_fp_saved_regs_size;
+	  poly_int64 fp_offset = frame.bytes_below_hard_fp - bytes_below_sp;
 	  if (hard_fp_valid_p)
 	    base_rtx = hard_frame_pointer_rtx;
 	  else
@@ -8868,12 +8867,13 @@ aarch64_save_callee_saves (poly_int64 start_offset,
 }
 
 /* Emit code to restore the callee registers from register number START
-   up to and including LIMIT.  Restore from the stack offset START_OFFSET,
-   skipping any write-back candidates if SKIP_WB is true.  Write the
-   appropriate REG_CFA_RESTORE notes into CFI_OPS.  */
+   up to and including LIMIT.  The stack pointer is currently BYTES_BELOW_SP
+   bytes above the bottom of the static frame.  Skip any write-back
+   candidates if SKIP_WB is true.  Write the appropriate REG_CFA_RESTORE
+   notes into CFI_OPS.  */
 
 static void
-aarch64_restore_callee_saves (poly_int64 start_offset, unsigned start,
+aarch64_restore_callee_saves (poly_int64 bytes_below_sp, unsigned start,
 			      unsigned limit, bool skip_wb, rtx *cfi_ops)
 {
   aarch64_frame &frame = cfun->machine->frame;
@@ -8899,7 +8899,9 @@ aarch64_restore_callee_saves (poly_int64 start_offset, unsigned start,
 
       machine_mode mode = aarch64_reg_save_mode (regno);
       reg = gen_rtx_REG (mode, regno);
-      offset = start_offset + frame.reg_offset[regno];
+      offset = (frame.reg_offset[regno]
+		+ frame.bytes_below_saved_regs
+		- bytes_below_sp);
       rtx base_rtx = stack_pointer_rtx;
       if (mode == VNx2DImode && BYTES_BIG_ENDIAN)
 	aarch64_adjust_sve_callee_save_base (mode, base_rtx, anchor_reg,
@@ -9675,8 +9677,6 @@ aarch64_expand_prologue (void)
   HOST_WIDE_INT callee_adjust = frame.callee_adjust;
   poly_int64 final_adjust = frame.final_adjust;
   poly_int64 sve_callee_adjust = frame.sve_callee_adjust;
-  poly_int64 below_hard_fp_saved_regs_size
-    = frame.below_hard_fp_saved_regs_size;
   unsigned reg1 = frame.wb_push_candidate1;
   unsigned reg2 = frame.wb_push_candidate2;
   bool emit_frame_chain = frame.emit_frame_chain;
@@ -9752,8 +9752,8 @@ aarch64_expand_prologue (void)
 			     - frame.hard_fp_offset);
   gcc_assert (known_ge (chain_offset, 0));
 
-  /* The offset of the bottom of the save area from the current SP.  */
-  poly_int64 saved_regs_offset = chain_offset - below_hard_fp_saved_regs_size;
+  /* The offset of the current SP from the bottom of the static frame.  */
+  poly_int64 bytes_below_sp = frame_size - initial_adjust - callee_adjust;
 
   if (emit_frame_chain)
     {
@@ -9761,7 +9761,7 @@ aarch64_expand_prologue (void)
 	{
 	  reg1 = R29_REGNUM;
 	  reg2 = R30_REGNUM;
-	  aarch64_save_callee_saves (saved_regs_offset, reg1, reg2,
+	  aarch64_save_callee_saves (bytes_below_sp, reg1, reg2,
 				     false, false);
 	}
       else
@@ -9801,7 +9801,7 @@ aarch64_expand_prologue (void)
       emit_insn (gen_stack_tie (stack_pointer_rtx, hard_frame_pointer_rtx));
     }
 
-  aarch64_save_callee_saves (saved_regs_offset, R0_REGNUM, R30_REGNUM,
+  aarch64_save_callee_saves (bytes_below_sp, R0_REGNUM, R30_REGNUM,
 			     callee_adjust != 0 || emit_frame_chain,
 			     emit_frame_chain);
   if (maybe_ne (sve_callee_adjust, 0))
@@ -9811,16 +9811,17 @@ aarch64_expand_prologue (void)
       aarch64_allocate_and_probe_stack_space (tmp1_rtx, tmp0_rtx,
 					      sve_callee_adjust,
 					      !frame_pointer_needed, false);
-      saved_regs_offset += sve_callee_adjust;
+      bytes_below_sp -= sve_callee_adjust;
     }
-  aarch64_save_callee_saves (saved_regs_offset, P0_REGNUM, P15_REGNUM,
+  aarch64_save_callee_saves (bytes_below_sp, P0_REGNUM, P15_REGNUM,
 			     false, emit_frame_chain);
-  aarch64_save_callee_saves (saved_regs_offset, V0_REGNUM, V31_REGNUM,
+  aarch64_save_callee_saves (bytes_below_sp, V0_REGNUM, V31_REGNUM,
 			     callee_adjust != 0 || emit_frame_chain,
 			     emit_frame_chain);
 
   /* We may need to probe the final adjustment if it is larger than the guard
      that is assumed by the called.  */
+  gcc_assert (known_eq (bytes_below_sp, final_adjust));
   aarch64_allocate_and_probe_stack_space (tmp1_rtx, tmp0_rtx, final_adjust,
 					  !frame_pointer_needed, true);
 }
@@ -9855,7 +9856,6 @@ aarch64_expand_epilogue (bool for_sibcall)
   poly_int64 initial_adjust = frame.initial_adjust;
   HOST_WIDE_INT callee_adjust = frame.callee_adjust;
   poly_int64 final_adjust = frame.final_adjust;
-  poly_int64 callee_offset = frame.callee_offset;
   poly_int64 sve_callee_adjust = frame.sve_callee_adjust;
   poly_int64 bytes_below_hard_fp = frame.bytes_below_hard_fp;
   unsigned reg1 = frame.wb_pop_candidate1;
@@ -9925,9 +9925,9 @@ aarch64_expand_epilogue (bool for_sibcall)
 
   /* Restore the vector registers before the predicate registers,
      so that we can use P4 as a temporary for big-endian SVE frames.  */
-  aarch64_restore_callee_saves (callee_offset, V0_REGNUM, V31_REGNUM,
+  aarch64_restore_callee_saves (final_adjust, V0_REGNUM, V31_REGNUM,
 				callee_adjust != 0, &cfi_ops);
-  aarch64_restore_callee_saves (callee_offset, P0_REGNUM, P15_REGNUM,
+  aarch64_restore_callee_saves (final_adjust, P0_REGNUM, P15_REGNUM,
 				false, &cfi_ops);
   if (maybe_ne (sve_callee_adjust, 0))
     aarch64_add_sp (NULL_RTX, NULL_RTX, sve_callee_adjust, true);
@@ -9935,7 +9935,7 @@ aarch64_expand_epilogue (bool for_sibcall)
   /* When shadow call stack is enabled, the scs_pop in the epilogue will
      restore x30, we don't need to restore x30 again in the traditional
      way.  */
-  aarch64_restore_callee_saves (callee_offset - sve_callee_adjust,
+  aarch64_restore_callee_saves (final_adjust + sve_callee_adjust,
 				R0_REGNUM, last_gpr,
 				callee_adjust != 0, &cfi_ops);
 
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index de68ff7202fc..94fca4b94716 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -907,10 +907,6 @@ struct GTY (()) aarch64_frame
      It is zero when no push is used.  */
   HOST_WIDE_INT callee_adjust;
 
-  /* The offset from SP to the callee-save registers after initial_adjust.
-     It may be non-zero if no push is used (ie. callee_adjust == 0).  */
-  poly_int64 callee_offset;
-
   /* The size of the stack adjustment before saving or after restoring
      SVE registers.  */
   poly_int64 sve_callee_adjust;
-- 
2.43.5