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Fix code generation error in gcc6809
It turned out that under some circumstances, the gcc optimizer would select
an instruction sequence that had the sense of a branch inverted. It seems
this was due to a particular instruction pattern included in the machine
description not being quite right with respect to how the condition codes
were tracked. Removing that instruction pattern seems to fix things
(subtraction with the arguments reversed). gcc seems to be smart enough to
figure out how to reorganize code to work without this reversed sense
subtraction and then do the right thing.
author | William Astle <lost@l-w.ca> |
---|---|
date | Thu, 24 Mar 2016 20:07:20 -0600 |
parents | b30091890d62 |
children |
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Introduction</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="LW Tool Chain" HREF="index.html"><LINK REL="PREVIOUS" TITLE="LW Tool Chain" HREF="index.html"><LINK REL="NEXT" TITLE="Output Formats" HREF="c21.html"></HEAD ><BODY CLASS="CHAPTER" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >LW Tool Chain</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="index.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="c21.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="AEN13" ></A >Chapter 1. Introduction</H1 ><P >The LW tool chain provides utilities for building binaries for MC6809 and HD6309 CPUs. The tool chain includes a cross-assembler and a cross-linker which support several styles of output.</P ><DIV CLASS="SECTION" ><H1 CLASS="SECTION" ><A NAME="AEN16" >1.1. History</A ></H1 ><P >For a long time, I have had an interest in creating an operating system for the Coco3. I finally started working on that project around the beginning of 2006. I had a number of assemblers I could choose from. Eventually, I settled on one and started tinkering. After a while, I realized that assembler was not going to be sufficient due to lack of macros and issues with forward references. Then I tried another which handled forward references correctly but still did not support macros. I looked around at other assemblers and they all lacked one feature or another that I really wanted for creating my operating system.</P ><P >The solution seemed clear at that point. I am a fair programmer so I figured I could write an assembler that would do everything I wanted an assembler to do. Thus the LWASM probject was born. After more than two years of on and off work, version 1.0 of LWASM was released in October of 2008.</P ><P >As the aforementioned operating system project progressed further, it became clear that while assembling the whole project through a single file was doable, it was not practical. When I found myself playing some fancy games with macros in a bid to simulate sections, I realized I needed a means of assembling source files separately and linking them later. This spawned a major development effort to add an object file support to LWASM. It also spawned the LWLINK project to provide a means to actually link the files.</P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="index.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="c21.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >LW Tool Chain</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Output Formats</TD ></TR ></TABLE ></DIV ></BODY ></HTML >