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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 2c24602be78f
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 LWASM Internals
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2 ===============
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3
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4 LWASM is a table-driven assembler that notionally uses two passes. However,
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5 it implements its assembly in several passes as follows.
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7 Pass 1
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8 ------
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10 This pass reads the entire source code and parses each line into an internal
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11 representation. Macros, file inclusions, and conditional assembly
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12 instructions are resolved at this point as well. Instructions with known
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13 sizes will have their sizes resolved at this point.
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15 Pass 2
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16 ------
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18 Check all exported symbols for validity and set them as imports if the
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19 assembler state says so. Also resolve all symbol references in all
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20 expressions to be direct references either to the symbol table or
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21 to the import list.
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23 Pass 3
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24 ------
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26 This pass resolves all instruction sizes that can be resolved without
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27 forcing any instruction sizes. This pass will run repeatedly until no
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28 no new resolution occurs.
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30 Pass 4
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31 ------
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33 Work through all un-resolved instructions and force sizes. After each size
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34 is forced, try re-resolving all other instructions. This is done starting
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35 at the beginning of the source and working forward. If any instruction does
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36 not resolve when forced, an error will be thrown.
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38 Pass 5
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39 ------
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41 Constantize all line addresses and throw errors if any cannot be. This
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42 pass will repeat until no further lines addresses are reduced to constants
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43 at which time all lines will be checked for constant-ness.
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45 Pass 6
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46 ------
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48 Finalize all expressions related to instructions. Carp about any that
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49 cannot be reduced to a usable form. That means, for the non-object target
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50 all expressions must resolve to a constant. For the object form, all
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51 expressions must resolve to symbol references and constants. Those symbol
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52 references may be internal or external.
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54 Pass 7
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55 ------
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57 Emit object code for each line for later output.