From 379fc8bbdc8372a7d09f75c35401d2008fe71de4 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Tue, 3 Aug 2004 04:15:32 +0000 Subject: [PATCH] Moved into SparcV9 directory llvm-svn: 15430 --- docs/RegisterAllocatorInfo.txt | 197 --------------------------------- 1 file changed, 197 deletions(-) delete mode 100644 docs/RegisterAllocatorInfo.txt diff --git a/docs/RegisterAllocatorInfo.txt b/docs/RegisterAllocatorInfo.txt deleted file mode 100644 index b20b6350201..00000000000 --- a/docs/RegisterAllocatorInfo.txt +++ /dev/null @@ -1,197 +0,0 @@ - =================== - Register Allocation - =================== - - -1. Introduction -=============== - -Purpose: This file contains implementation information about register - allocation. -Author : Ruchira Sasanka -Date : Dec 8, 2001 - - -2. Entry Point -============== -class PhyRegAlloc (PhyRegAlloc.h) is the main class for the register -allocation. PhyRegAlloc::allocateRegisters() starts the register allocation -and contains the major steps for register allocation. - -2. Usage -======== -Register allocation must be done as: - - MethodLiveVarInfo LVI(*MethodI ); // compute LV info - LVI.analyze(); - - TargetMachine &target = .... // target description - - - PhyRegAlloc PRA(*MethodI, target, &LVI); // allocate regs - PRA.allocateRegisters(); - - -4. Input and Preconditions -========================== -Register allocation is done using machine instructions. The constructor -to the class takes a pointer to a method, a target machine description and -a live variable information for the method. - -The preconditions are: - -1. Instruction selection is complete (i.e., machine instructions are - generated) for the method before the live variable analysis - -2. Phi elimination is complete. - - -5. Assumptions -============== - - All variables (llvm Values) are defined before they are used. However, a - constant may not be defined in the machine instruction stream if it can be - used as an immediate value within a machine instruction. However, register - allocation does not have to worry about immediate constants since they - do not require registers. - - Since an llvm Value has a list of uses associated, it is sufficient to - record only the defs in a Live Range. - - - - -6. Overall Design -================= -There are sperate reigster classes - e.g., Int, Float, -IntConditionCode, FloatConditionCode register classes for Sparc. - -Registerallocation consists of the following main steps: - - 1. Construct Live-ranges & Suggest colors (machine specific) if required - 2. Create Interference graphs - 3. Coalescing live ranges - 4. Color all live ranges in each RegClass using graph coloring algo - 5. Insert additional (machine specific) code for calls/returns/incoming args - 6. Update instruction stream and insert spill code - -All the above methods are called from PhyRegAlloc::allocateRegisters(). - -All steps above except step 5 and suggesting colors in step 1 are indepenedent -of a particular target architecture. Targer independent code is availble in -../lib/CodeGen/RegAlloc. Target specific code for Sparc is available in -../lib/Target/Sparc. - - -6.1. Construct Live-ranges & Suggest colors (machine specific) if required --------------------------------------------------------------------------- -Live range construction is done using machine instructions. Since there must -be at least one definition for each variable in the machine instruction, we -consider only definitions in creating live ranges. After live range -construction is complete, there is a live range for all variables defined in -the instruction stream. Note however that, live ranges are not constructed for -constants which are not defined in the instruction stream. - -A LiveRange is a set of Values (only defs) in that live range. Live range -construction is done in combination for all register classes. All the live -ranges for a method are entered to a LiveRangeMap which can be accessed using -any Value in the LiveRange. - -After live ranges have been constructed, we call machine specific code to -suggest colors for speical live ranges. For instance, incoming args, call args, -return values must be placed in special registers for most architectures. By -suggesting colors for such special live ranges before we do the actual register -allocation using graph coloring, the graph coloring can try its best to assign -the required color for such special live ranges. This will reduce unnecessary -copy instructions needed to move values to special registers. However, there -is no guarantee that a live range will receive its suggested color. If the -live range does not receive the suggested color, we have to insert explicit -copy instructions to move the value into requred registers and its done in -step 5 above. - -See LiveRange.h, LiveRangeInfo.h (and LiveRange.cpp, LiveRangeInfo.cpp) for -algorithms and details. See SparcRegInfo.cpp for suggesting colors for -incoming/call arguments and return values. - - -6.2. Create Interference graphs -------------------------------- -Once live ranges are constructed, we can build interference graphs for each -register class. Though each register class must have a separate interference -graph, building all interference graphs is performed in one pass. Also, the -adjacency list for each live range is built in this phase. Consequently, each -register class has an interference graph (which is a bit matrix) and each -LiveRange has an adjacency list to record its neighbors. Live variable info -is used for finding the interferences. - -See IGNode.h, InterferenceGraph.h (and IGNode.h, InterferenceGraph.h) for -data structures and PhyRegAlloc::createIGNodeListsAndIGs() for the starting -point for interference graph construction. - - -6.3. Coalescing live ranges ---------------------------- -We coalesce live ranges to reduce the number of live ranges. - -See LiveRangeInfo.h (and LiveRangeInfo.cpp). The entire algorithm for -coalesing is given in LiveRangeInfo::coalesceLRs(). - - -6.4. Color all live ranges in each RegClass using graph coloring algo ---------------------------------------------------------------------- -Each register class is colored separately using the graph coloring algo. When -assigning colors, preference is given to live ranges with suggested colors -so that if such a live range receives a color (i.e., not spilled), then -we try to assign the color suggested for that live range. When this phase -is complete it is possible that some live ranges do not have colors (i.e., -those that must be spilled). - - -6.5. Insert additional (machine specific) code for calls/returns/incoming args ------------------------------------------------------------------------------- -This code is machine specific. Currently, the code for Sparc is implemented -in SparcRegInfo.cpp. This code is more complex because of the complex -requirements of assigning some values to special registers. When a special -value as an incoming argument receives a color through the graph coloring -alogorithm, we have to make sure that it received the correct color (for -instance the first incoming int argument must be colored to %i0 on Sparc). If -it didn't receive the correct color, we have to insert instruction to to move -the value to the required register. Also, this phase produces the caller -saving code. All adition code produced is kept separately until the last -phase (see 6.6) - - -6.6. Update instruction stream and insert spill code ------------------------------------------------------ -After we have assigned registers for all values and after we have produced -additional code to be inserted before some instructions, we update the -machine instruction stream. While we are updating the machine instruction -stream, if an instruction referes to a spilled value, we insert spill -instructions before/after that instruction. Also, we prepend/append additonal -instructions that have been produced for that instruction by the register -allocation (e.g., caller saving code) - - -7. Furture work -=============== -If it is necessary to port the register allocator to another architecture -than Sparc, only the target specific code in ../lib/Target/Sparc needs to -be rewritten. Methods defined in class MachineRegInfo must be provided for -the new architecure. - -7.1 Using ReservedColorList in RegClass ----------------------------------------- -The register allocator allows reserving a set of registers - i.e. the reserved -registers are not used by the register allocator. Currently, there are no -reserved registers. It it is necessary to make some registers unavailable to -a particular method, this feature will become handy. To do that, the reserved -register list must be passed to the register allocator. See PhyRegAlloc.cpp - - -7.2 %g registers on Sparc -------------------------- -Currently, %g registers are not allocated on Sparc. If it is necessary to -allocate these %g registers, the enumeration of registers in SparcIntRegClass -in SparcRegClassInfo.h must be changed. %g registers can be easily added as -volatile registers just by moving them above in the eneumeration - see -SparcRegClassInfo.h