com.ibm.wala.ssa

Interface SSAIndirectionData<T extends SSAIndirectionData.Name>

All Known Implementing Classes:

ShrikeIndirectionData

public interface SSAIndirectionData<T extends SSAIndirectionData.Name>

A mapping that tells, for a given instruction s, what "names" does s def and use indirectly.

For example, an SSALoadIndirectInstruction takes as an argument a pointer value. This map tells which locals that pointer may alias.

So if we have

Example A:

 v2 = SSAAddressOf v1;
 v7 = #1;
 v3 = SSALoadIndirect v2; (1)
 

Then this map will tell us that instruction (1) indirectly uses whichever source-level entity (in the source or bytecode) v1 represents.

(Don't be confused by AddressOf v1 .. we're not actually taking the address of v1 ... we're taking the address of some source level entity (like a local variable in source code or bytecode) for which v1 is just an SSA name)

As a more complex example, when we have lexical scoping, we can have the following IR generated, which passes a local by reference:

Example B: foo: v3 = AddressOf v2; bar(v3) (1) bar(v1): StoreIndirect v1, #7.

In this case, the instruction (1) potentially defs the locals aliased by v2. The lexical scoping support could/should use this information to rebuild SSA accounting for the fact that (1) defs v2.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	SSAIndirectionData.Name A Name is a mock interface introduced just for strong typing.

Method Summary

Modifier and Type	Method and Description
int	getDef(int instructionIndex, T name) For the instruction at the given index, and a source-level name, return the SSA value number which represents this instruction's def of that name.
java.util.Collection<T>	getNames() Returns the set of "source" level names (e.g.
int	getUse(int instructionIndex, T name) For the instruction at the given index, and a source-level name, return the SSA value number which represents this instruction's use of that name.
void	setDef(int instructionIndex, T name, int newDef) Record the fact that a particular instruction defs a particular SSA value number (newDef), representing the value of a "source" entity "name".
void	setUse(int instructionIndex, T name, int newUse)

Method Detail

getNames

java.util.Collection<T> getNames()

Returns the set of "source" level names (e.g. local variables in bytecode or source code) for which this map holds information.

getDef

int getDef(int instructionIndex,
           T name)

For the instruction at the given index, and a source-level name, return the SSA value number which represents this instruction's def of that name.

For example, in Example B in header comment above, suppose v2 referred to a "source"-entity called "Local1". Since instruction (1) (call to bar) defs "Local1", we introduce in this table a new SSA value number, say v7, which represents the value of "Local1" immediately after this instruction.

setDef

void setDef(int instructionIndex,
            T name,
            int newDef)

Record the fact that a particular instruction defs a particular SSA value number (newDef), representing the value of a "source" entity "name".

See Also:

getDef(int, T)

getUse

int getUse(int instructionIndex,
           T name)

For the instruction at the given index, and a source-level name, return the SSA value number which represents this instruction's use of that name.

For example, in Example A in header comment above, suppose v1 referred to a "source"-entity called "Local1". Since instruction (1) (LoadIndirect) uses "Local1", we record in this table the SSA value number that represents "Local1" immediately before instruction (1). So if v1 and v7 both refer to "Local1", then (1) uses v7. If v7 does NOT refer to "Local1", then (1) uses v1.

setUse

void setUse(int instructionIndex,
            T name,
            int newUse)

See Also:

getUse(int, T)