org.jikesrvm.compilers.opt.regalloc

Class Coalesce

java.lang.Object

org.jikesrvm.compilers.opt.regalloc.Coalesce

class Coalesce
extends Object

Utility to help coalesce registers.

See Also:

CoalesceMoves

Field Summary

Fields

Modifier and Type	Field and Description
private Map<Instruction,Integer>	instNumbers

Constructor Summary

Constructors

Constructor and Description
Coalesce(Map<Instruction,Integer> instNumbers)

Method Summary

Modifier and Type	Method and Description
boolean	attempt(LiveAnalysis live, Register r1, Register r2) Attempt to coalesce register r2 into register r1.
private boolean	isLiveAtDef(Register r1, Register r2, LiveAnalysis live) Is register r1 live at any def of register r2?
private boolean	split(Register r1, Register r2) Is there an instruction r1 = split r2 or r2 = split r1??

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

instNumbers

private final Map<Instruction,Integer> instNumbers

Constructor Detail

Coalesce

Coalesce(Map<Instruction,Integer> instNumbers)

Method Detail

attempt

public boolean attempt(LiveAnalysis live,
                       Register r1,
                       Register r2)

Attempt to coalesce register r2 into register r1. If this is legal,

• rewrite all defs and uses of r2 as defs and uses of r1
• update the liveness information
• update the def-use chains

PRECONDITION def-use chains must be computed and valid.

Parameters:

live - liveness information for the IR

r1 - the register that is the target of coalescing (i.e. the one that will remain)

r2 - the register that we want to coalesce (i.e. the one that will be "removed")

Returns:

true if the transformation succeeded, false otherwise.

isLiveAtDef

private boolean isLiveAtDef(Register r1,
                            Register r2,
                            LiveAnalysis live)

Is register r1 live at any def of register r2?

PRECONDITION def-use chains must be computed and valid.

Note: this implementation is not efficient. The liveness data structures must be re-designed to support this efficiently.

Parameters:

r1 - the register that is checked for liveness

r2 - the register whose defs are checked against liveness

live - live analysis phase

Returns:

true if the register is live at any point where the other register is defined

split

private boolean split(Register r1,
                      Register r2)

Is there an instruction r1 = split r2 or r2 = split r1??

Parameters:

r1 - a register

r2 - another register

Returns:

true if there's an operation that's a split and has occurrences of both registers