IR Representation

Hi,


For learning purpose I am writing a compiler for a small subset of the C
language. I intend to implement a few simple optimizations in the IR and
also to support at least two target ISAs (x86-64 and some ARM). I would
also like to use a tree pattern matching Inst. Selection. However, I am
struggling on how to store/represent the IR.


Given the above objectives which way to represent the IR would be better? A
linear sequence of instructions or a tree? My thoughts on this are as
follow:


- I believe that a linear sequence of instructions would be easier to
optimize/analyze, right? However, a tree seems better given that I want to
use a tree pattern matching instruction selection.


- I could use a linear representation for optimization and later convert
the IR to a tree-like format before instruction selection. However, this
conversion seems not so easy...


- Currently, I intend to use a single, tree-like, IR since I can extract a
linear order from the tree and it suits well the instruction selection
algorithm.


Besides, I have a question about storing the IR as a tree. Should I
(a) create an individual tree for each expression/statement in the
source or (b) should I create a single tree concatenating the trees
for each expression?


- Option (a) seems much simpler to create, but I believe the trees would be
very small, possibly degrading the efficiency of the tree pattern matching
instruction selection algorithm. [Currently, this is the format that I
intend to use.]


- I believe option (b) create the opportunity for matching larger patterns
and thus could improve performance. But there is a lot of redundant
nodes/code in this representation and it also seems harder to implement
than option (a).


I have read a few books/papers about these things but as you can see I
still have a lot of questions. I would really like to hear your comments
about the above topics!




Thank you,
CC)sar.

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