From b697094c587ef07be04e0c6de0cb5c61bd26453c Mon Sep 17 00:00:00 2001
From: Stephen Heumann <stephenheumann@gmail.com>
Date: Fri, 12 Jan 2018 22:28:47 -0600
Subject: [PATCH] Generate more efficient stack repair code (1).

Previously, when stack repair code was generated, it always included instructions to save and restore a previously-saved stack position, but this was only actually used for function calls nested within the arguments to other function calls using stack repair code. Now that code is only generated in cases where it is needed, and the stack repair code for other calls is simplified to omit it.

This optimization affects all (non-nested) function calls when not using optimize bit 3, and varargs function calls when not using optimize bit 6.
---
 Gen.pas | 46 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 33 insertions(+), 13 deletions(-)

diff --git a/Gen.pas b/Gen.pas
index 3ac42f7..408e8be 100644
--- a/Gen.pas
+++ b/Gen.pas
@@ -66,6 +66,7 @@ var
    gLong: longType;                     {info about last long value}
    namePushed: boolean;			{has a name been pushed in this proc?}
    skipLoad: boolean;			{skip load for a pc_lli, etc?}
+   stackSaveDepth: integer;		{nesting depth of saved stack positions}
 
                                         {stack frame locations}
                                         {---------------------}
@@ -4026,13 +4027,16 @@ procedure GenTree {op: icptr};
       lab1: integer;			{return point}
       lLong: longType;			{used to reserve gLong}
 
-   begin {GenCup}
+   begin {GenCui}
    {save the stack register}
    if saveStack or checkStack or (op^.q <> 0) then begin
-      GenNative(m_ldx_dir, direct, stackLoc, nil, 0);
-      GenImplied(m_phx);
+      if stackSaveDepth <> 0 then begin
+         GenNative(m_ldx_dir, direct, stackLoc, nil, 0);
+         GenImplied(m_phx);
+         end; {if}
       GenImplied(m_tsx);
       GenNative(m_stx_dir, direct, stackLoc, nil, 0);
+      stackSaveDepth := stackSaveDepth + 1;
       end; {if}
 
    {generate parameters}
@@ -4067,18 +4071,24 @@ procedure GenTree {op: icptr};
 
    if checkStack then begin
       {check the stack for errors}
+      stackSaveDepth := stackSaveDepth - 1;
       GenNative(m_ldy_dir, direct, stackLoc, nil, 0);
       GenCall(76);
-      GenImplied(m_ply);
-      GenNative(m_sty_dir, direct, stackLoc, nil, 0);
+      if stackSaveDepth <> 0 then begin
+         GenImplied(m_ply);
+         GenNative(m_sty_dir, direct, stackLoc, nil, 0);
+         end; {if}
       end {if}
    else if saveStack or (op^.q <> 0) then begin
+      stackSaveDepth := stackSaveDepth - 1;
       GenImplied(m_txy);
       GenNative(m_ldx_dir, direct, stackLoc, nil, 0);
       GenImplied(m_txs);
       GenImplied(m_tyx);
-      GenImplied(m_ply);
-      GenNative(m_sty_dir, direct, stackLoc, nil, 0);
+      if stackSaveDepth <> 0 then begin
+         GenImplied(m_ply);
+         GenNative(m_sty_dir, direct, stackLoc, nil, 0);
+         end; {if}
       end; {else}
 
    {save the returned value}
@@ -4097,10 +4107,13 @@ procedure GenTree {op: icptr};
    begin {GenCup}
    {save the stack register}
    if saveStack or checkStack or (op^.q <> 0) then begin
-      GenNative(m_ldx_dir, direct, stackLoc, nil, 0);
-      GenImplied(m_phx);
+      if stackSaveDepth <> 0 then begin
+         GenNative(m_ldx_dir, direct, stackLoc, nil, 0);
+         GenImplied(m_phx);
+         end; {if}
       GenImplied(m_tsx);
       GenNative(m_stx_dir, direct, stackLoc, nil, 0);
+      stackSaveDepth := stackSaveDepth + 1;
       end; {if}
 
    {generate parameters}
@@ -4113,18 +4126,24 @@ procedure GenTree {op: icptr};
 
    {check the stack for errors}
    if checkStack then begin
+      stackSaveDepth := stackSaveDepth - 1;
       GenNative(m_ldy_dir, direct, stackLoc, nil, 0);
       GenCall(76);
-      GenImplied(m_ply);
-      GenNative(m_sty_dir, direct, stackLoc, nil, 0);
+      if stackSaveDepth <> 0 then begin
+         GenImplied(m_ply);
+         GenNative(m_sty_dir, direct, stackLoc, nil, 0);
+         end; {if}
       GenImplied(m_tay);
       end {if}
    else if saveStack or (op^.q <> 0) then begin
+      stackSaveDepth := stackSaveDepth - 1;
       GenImplied(m_tay);
       GenNative(m_lda_dir, direct, stackLoc, nil, 0);
       GenImplied(m_tcs);
-      GenImplied(m_pla);
-      GenNative(m_sta_dir, direct, stackLoc, nil, 0);
+      if stackSaveDepth <> 0 then begin
+         GenImplied(m_pla);
+         GenNative(m_sta_dir, direct, stackLoc, nil, 0);
+         end; {if}
       GenImplied(m_tya);
       end; {else}
 
@@ -5647,6 +5666,7 @@ parameterSize := 0;
 funLoc := 0;
 dworkLoc := 0;
 minSize := 1;
+stackSaveDepth := 0;
 while bk <> nil do begin 
    op := bk^.code;
    while op <> nil do begin