harpoon.Analysis.Tree
Class DominatingMemoryAccess

java.lang.Object
  harpoon.Analysis.Tree.DominatingMemoryAccess

public class DominatingMemoryAccess
extends Object

DominatingMemoryAccess is an analysis that uses information about memory operations to determine which of them need to do cache tag checks, and which don't. If one access dominates another, and they are provably on the same cache line, we do not need to check the later's tag. We assume that the system allocator does not break objects over cache lines. We assign direct address register numbers to the most important references. The defining access set the register to point to the cache location of the data, and the using accesses, um, use the data at that cache location. This is a standard register allocation problem, but we don't spill, since the contents of a direct address register is a hardware decoded cache location which is kept consistent in the face of replacements by the hardware. To restore an old value of the register would potentially allow a process access into protected data. Anyway, there is no CPU interface to get at the contents of direct address registers for precisely the reason that it shouldn't use them. The backend needs to know which direct address register numbers we used since it needs to invalidate them on a function return.

Version:

$Id: DominatingMemoryAccess.java,v 1.6 2004/02/08 03:20:34 cananian Exp $

Author:

Emmett Witchel <witchel@mit.edu>

Nested Class Summary

class

DominatingMemoryAccess.daNum

Constructor Summary

DominatingMemoryAccess(HCodeFactory parent, Frame frame, ClassHierarchy ch)

Method Summary

HCodeFactory	codeFactory() Standard interface to run this analysis
static boolean	isDef(Object _danum) Returns true if the MEM operation that returned this specifier (from harpoon.Backend.MIPS.Frame.daNum) is the defining access.
static boolean	isUse(Object _danum) Returns true if the MEM operation that returned this specifier (from harpoon.Backend.MIPS.Frame.daNum) is a use.
static int	num(Object _danum) Returns the direct address register used by the MEM operation that returned this specifier (from harpoon.Backend.MIPS.Frame.daNum).

Methods inherited from class java.lang.Object

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

Constructor Detail

DominatingMemoryAccess

public DominatingMemoryAccess(HCodeFactory parent,
                              Frame frame,
                              ClassHierarchy ch)

Method Detail

isDef

public static boolean isDef(Object _danum)

Returns true if the MEM operation that returned this specifier (from harpoon.Backend.MIPS.Frame.daNum) is the defining access. A defining access does a tag check for the cache line it is on.

isUse

public static boolean isUse(Object _danum)

Returns true if the MEM operation that returned this specifier (from harpoon.Backend.MIPS.Frame.daNum) is a use. A use memory access can skip the tag check, since it has been done for this line.

num

public static int num(Object _danum)

Returns the direct address register used by the MEM operation that returned this specifier (from harpoon.Backend.MIPS.Frame.daNum). A direct address register is an on-cache register that points to a specific cache location. You can think of it as a cache line identifier. A dominant accesses might do the tag check and set direct address register 3. A subordinate access can skip the tag check, and use direct address register 3 instead. The direct address register number substitutes for the virtual address to identify the cache line.

codeFactory

public HCodeFactory codeFactory()

Standard interface to run this analysis