AsmUnparser.C File Reference

#include "sage3basic.h"
#include "AsmUnparser.h"
#include "AsmUnparser_compat.h"

Include dependency graph for AsmUnparser.C:

Functions
static std::vector< bool >	build_noop_index (const std::vector< std::pair< size_t, size_t > > &noops)
	Returns a vector of booleans indicating whether an instruction is part of a no-op sequence.

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Function Documentation

static std::vector<bool> build_noop_index

(

const std::vector< std::pair< size_t, size_t > > &

noops

)

[static]

Returns a vector of booleans indicating whether an instruction is part of a no-op sequence.

The sequences returned by SgAsmInstruction::find_noop_subsequences() can overlap, but we cannot assume that removing overlapping sequences will result in a meaningful basic block. For instance, consider the following block:

      1: mov eax, 1
      2: mov eax, 2
      3: mov eax, 1
      4: mov eax, 2

The subsequences <2,3> and <3,4> are both no-ops when considered independently. However, we cannot remove all four instructions because the sequence <1,2,3,4> is not a no-op.

Therefore, this function takes the list returned by find_noop_subsequences and greedily selects the longest non-overlapping sequences, and returns a vector indexed by instruction position and containing a boolean to indicate whether that instruction is part of a selected no-op sequence. Note that this algorithm does not necessarily maximize the number of no-op instructions.

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