Discover and eliminate split conditions. More...

#include <blockaction.hh>

Classes
struct	MergePair
	A pair of Varnode objects that have been split (and should be merged) More...

Public Member Functions
	ConditionalJoin (Funcdata &fd)
	Constructor.

bool	match (BlockBasic b1, BlockBasic b2)
	Test blocks for the merge condition. More...

void	execute (void)
	Execute the merge. More...

void	clear (void)
	Clear for a new test.

Private Member Functions
bool	findDups (void)
	Search for duplicate conditional expressions. More...

void	checkExitBlock (BlockBasic *exit, int4 in1, int4 in2)
	Look for additional Varnode pairs in an exit block that need to be merged. More...

void	cutDownMultiequals (BlockBasic *exit, int4 in1, int4 in2)
	Substitute new joined Varnode in the given exit block. More...

void	setupMultiequals (void)
	Join the Varnodes in the new joinblock. More...

void	moveCbranch (void)
	Remove the other CBRANCH.

Private Attributes
Funcdata &	data
	The function being analyzed.

BlockBasic *	block1
	Side 1 of the (putative) split.

BlockBasic *	block2
	Side 2 of the (putative) split.

BlockBasic *	exita
	First (common) exit point.

BlockBasic *	exitb
	Second (common) exit point.

int4	a_in1
	In edge of exita coming from block1.

int4	a_in2
	In edge of exita coming from block2.

int4	b_in1
	In edge of exitb coming from block1.

int4	b_in2
	In edge of exitb coming from block2.

PcodeOp *	cbranch1
	CBRANCH at bottom of block1.

PcodeOp *	cbranch2
	CBRANCH at bottom of block2.

BlockBasic *	joinblock
	The new joined condition block.

map< MergePair, Varnode * >	mergeneed
	Map from the MergePair of Varnodes to the merged Varnode.

Detailed Description

Discover and eliminate split conditions.

A split condition is when a conditional expression, resulting in a CBRANCH, is duplicated across two blocks that would otherwise merge. Instead of a single conditional in a merged block, there are two copies of the conditional, two splitting blocks and no direct merge.

Member Function Documentation

◆ checkExitBlock()

void ghidra::ConditionalJoin::checkExitBlock	(	BlockBasic *	exit,
		int4	in1,
		int4	in2
	)

private

Look for additional Varnode pairs in an exit block that need to be merged.

Varnodes that are merged in the exit block flowing from block1 and block2 will need to merged in the new joined block. Add these pairs to the mergeneed map.

Parameters

exit	is the exit block
in1	is the index of the edge coming from block1
in2	is the index of the edge coming from block2

References ghidra::BlockBasic::beginOp(), ghidra::PcodeOp::code(), ghidra::CPUI_COPY, ghidra::CPUI_MULTIEQUAL, ghidra::BlockBasic::endOp(), and ghidra::PcodeOp::getIn().

◆ cutDownMultiequals()

void ghidra::ConditionalJoin::cutDownMultiequals	(	BlockBasic *	exit,
		int4	in1,
		int4	in2
	)

private

Substitute new joined Varnode in the given exit block.

For any MULTIEQUAL in the exit, given two input slots, remove one Varnode, and substitute the other Varnode from the corresponding Varnode in the mergeneed map.

Parameters

exit	is the exit block
in1	is the index of the incoming edge from block1
in2	is the index of the incoming edge from block2

References ghidra::BlockBasic::beginOp(), ghidra::PcodeOp::code(), ghidra::CPUI_COPY, ghidra::CPUI_MULTIEQUAL, ghidra::BlockBasic::endOp(), ghidra::PcodeOp::getIn(), and ghidra::PcodeOp::numInput().

◆ execute()

void ghidra::ConditionalJoin::execute ( void )

Execute the merge.

All the conditions have been met. Go ahead and do the join.

Referenced by ghidra::ActionNodeJoin::apply().

◆ findDups()

bool ghidra::ConditionalJoin::findDups ( void )

private

Search for duplicate conditional expressions.

Given two conditional blocks, determine if the corresponding conditional expressions are equivalent, up to Varnodes that need to be merged. Any Varnode pairs that need to be merged are put in the mergeneed map.

Returns: true if there are matching conditions

References ghidra::PcodeOp::code(), ghidra::CPUI_CBRANCH, ghidra::CPUI_COPY, ghidra::CPUI_SUBPIECE, ghidra::Varnode::getDef(), ghidra::Varnode::isSpacebase(), and ghidra::Varnode::isWritten().

◆ match()

bool ghidra::ConditionalJoin::match	(	BlockBasic *	b1,
		BlockBasic *	b2
	)

Test blocks for the merge condition.

Given a pair of conditional blocks, make sure that they match the split conditions necessary for merging and set up to do the merge. If the conditions are not met, this method cleans up so that additional calls can be made.

Parameters