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Implement dead code elimination #145

Merged
merged 2 commits into from
Aug 14, 2024
Merged

Implement dead code elimination #145

merged 2 commits into from
Aug 14, 2024

Commits on Aug 12, 2024

  1. Fix error with return statement in for-loop body 

    This error occurred when a return statement was in for-loop body. After
parsing loop body, "body_" was assigned NULL as the return value,
causing the compiler to failed in correctly connect "inc_" and
"cond_start" basic blocks.

This error can be analyzed by examining the CFG.dot file.
    @nosba0957
    nosba0957 committed Aug 12, 2024
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  2. Implement dead code elimination 

    Introduces the creaetion of reverse dominance frontier (RDF) to support
dead code elimination (DCE). Method for implementing RDF is similar to
that of dominance frontier (DF). The key difference is that RDF is
computed on the reverse CFG. In other words, operations were performed
on "prev[]" which in the basic block structure, now switched to operate
on "next", "then_" and "else_".

In the "dce_insn" function, mark useful instructions during the initial
analysis of the current basic block. Continue identifying useful
instructions by tracing back from the last assigned instruction of the
both operands of the current "insn". In the "dce_sweep" function remove
the useless instruction from the current "insn_list". If a branch
instruction is encountered, remove it and reconnect the current basic
block to its reverse immediate dominator.

Before implementing DCE, compiling "src/main.c" resulted in an
executable with 51,357 instructions for ARMv7-A. After DCE, the
executable was 51,330 instructions, reducing the total by 27
instructions.
    @nosba0957
    nosba0957 committed Aug 12, 2024
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