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

Coalesce

Coalesce()

attempt

public static boolean attempt(IR ir,
                              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. PRECONDITION instructions are numbered, with numbers stored in Instruction.scratch

Parameters:

ir - the governing IR

live - liveness information for the IR

r1 -

r2 -

Returns:

true if the transformation succeeded, false otherwise.

isLiveAtDef

private static 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. PRECONDITION instructions are numbered, with numbers stored in Instruction.scratch

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

split

private static boolean split(Register r1,
                             Register r2)

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