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cjmp cond .loop .end
- Boolean expressions are simplified as described in section 8.4 of the
- Dragon book
+ Boolean expressions are simplified to a location to jump to, as
+ described in section 8.4 of the Dragon book.
3.2. Complex Expressions:
+ Complex expressions such as copying types larger than a single machine
+ word, pulling members out of structures, emulated multiplication and
+ division for larger integers sizes, and similar operations are reduced
+ to trees that are expressible in terms of simple machine operations.
+ By the end of the simplification pass, the following operators should
+ not be present in the trees:
+ Obad Oret Opreinc Opostinc Opredec Opostdec Olor Oland Oaddeq
+ Osubeq Omuleq Odiveq Omodeq Oboreq Obandeq Obxoreq Obsleq
+ Obsreq Omemb Oslice Oidx Osize Numops Oucon Ouget Otup Oarr
+ Oslbase Osllen Ocast
+ Currently, there is virtually no optimization done on the trees after
+ flattening. The only optimization that is done is constant folding.
4.1. Constant Folding:
+ Expressions with constant values are simplified algebraically. For
+ example, the expression 'x*1' is simplified to simply 'x', '0/n' is
+ simplified to '0', and so on.
5. CODE GENERATION:
5.1. Instruction Selection:
+ Instruction selection is done via a simple hand written bottom up pass
+ over the tree. Common patterns such as scaled or offset indexing are
+ recognized by the patterns, but no attempts at finding an optimal
+ tiling are made.
5.2. Register Allocation:
+ Register allocation is done via the algorithm described in "Iterated
+ Regster Coalescing", by Appel and George. As of the time of this
+ writing, the register allocator does not yet implement overlapping
+ register classes. This will be done as described in "A generalized
+ algorithm for graph-coloring register allocation", by Smith, Ramsey,
+ and Holloway.
6: TUTORIAL: ADDING A STATEMENT:
6.1. Stubbing in the node types: