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llvm-mirror/lib/CodeGen/RegAlloc/LiveRangeInfo.cpp
Vikram S. Adve 194a5862e0 Extensive changes to the way code generation occurs for function 
call arguments and return values:
Now all copy operations before and after a call are generated during
selection instead of during register allocation.
The values are copied to virtual registers (or to the stack), but
in the former case these operands are marked with the correct physical
registers according to the calling convention.
Although this complicates scheduling and does not work well with
live range analysis, it simplifies the machine-dependent part of
register allocation.

llvm-svn: 6465
2003-05-31 07:32:01 +00:00

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//===-- LiveRangeInfo.cpp -------------------------------------------------===//
//
// Live range construction for coloring-based register allocation for LLVM.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/LiveRangeInfo.h"
#include "RegAllocCommon.h"
#include "RegClass.h"
#include "llvm/CodeGen/IGNode.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Function.h"
#include "Support/SetOperations.h"
using std::cerr;
unsigned LiveRange::getRegClassID() const { return getRegClass()->getID(); }
LiveRangeInfo::LiveRangeInfo(const Function *F, const TargetMachine &tm,
std::vector<RegClass *> &RCL)
: Meth(F), TM(tm), RegClassList(RCL), MRI(tm.getRegInfo()) { }
LiveRangeInfo::~LiveRangeInfo() {
for (LiveRangeMapType::iterator MI = LiveRangeMap.begin();
MI != LiveRangeMap.end(); ++MI) {
if (MI->first && MI->second) {
LiveRange *LR = MI->second;
// we need to be careful in deleting LiveRanges in LiveRangeMap
// since two/more Values in the live range map can point to the same
// live range. We have to make the other entries NULL when we delete
// a live range.
for (LiveRange::iterator LI = LR->begin(); LI != LR->end(); ++LI)
LiveRangeMap[*LI] = 0;
delete LR;
}
}
}
//---------------------------------------------------------------------------
// union two live ranges into one. The 2nd LR is deleted. Used for coalescing.
// Note: the caller must make sure that L1 and L2 are distinct and both
// LRs don't have suggested colors
//---------------------------------------------------------------------------
void LiveRangeInfo::unionAndUpdateLRs(LiveRange *L1, LiveRange *L2) {
assert(L1 != L2 && (!L1->hasSuggestedColor() || !L2->hasSuggestedColor()));
assert(! (L1->hasColor() && L2->hasColor()) ||
L1->getColor() == L2->getColor());
set_union(*L1, *L2); // add elements of L2 to L1
for(ValueSet::iterator L2It = L2->begin(); L2It != L2->end(); ++L2It) {
//assert(( L1->getTypeID() == L2->getTypeID()) && "Merge:Different types");
L1->insert(*L2It); // add the var in L2 to L1
LiveRangeMap[*L2It] = L1; // now the elements in L2 should map
//to L1
}
// set call interference for L1 from L2
if (L2->isCallInterference())
L1->setCallInterference();
// add the spill costs
L1->addSpillCost(L2->getSpillCost());
// If L2 has a color, give L1 that color. Note that L1 may have had the same
// color or none, but would not have a different color as asserted above.
if (L2->hasColor())
L1->setColor(L2->getColor());
// Similarly, if LROfUse(L2) has a suggested color, the new range
// must have the same color.
if (L2->hasSuggestedColor())
L1->setSuggestedColor(L2->getSuggestedColor());
delete L2; // delete L2 as it is no longer needed
}
//---------------------------------------------------------------------------
// Method for creating a single live range for a definition.
// The definition must be represented by a virtual register (a Value).
// Note: this function does *not* check that no live range exists for def.
//---------------------------------------------------------------------------
LiveRange*
LiveRangeInfo::createNewLiveRange(const Value* Def, bool isCC /* = false*/)
{
LiveRange* DefRange = new LiveRange(); // Create a new live range,
DefRange->insert(Def); // add Def to it,
LiveRangeMap[Def] = DefRange; // and update the map.
// set the register class of the new live range
DefRange->setRegClass(RegClassList[MRI.getRegClassIDOfType(Def->getType(),
isCC)]);
if (DEBUG_RA >= RA_DEBUG_LiveRanges) {
cerr << " Creating a LR for def ";
if (isCC) cerr << " (CC Register!)";
cerr << " : " << RAV(Def) << "\n";
}
return DefRange;
}
LiveRange*
LiveRangeInfo::createOrAddToLiveRange(const Value* Def, bool isCC /* = false*/)
{
LiveRange *DefRange = LiveRangeMap[Def];
// check if the LR is already there (because of multiple defs)
if (!DefRange) {
DefRange = createNewLiveRange(Def, isCC);
} else { // live range already exists
DefRange->insert(Def); // add the operand to the range
LiveRangeMap[Def] = DefRange; // make operand point to merged set
if (DEBUG_RA >= RA_DEBUG_LiveRanges)
cerr << " Added to existing LR for def: " << RAV(Def) << "\n";
}
return DefRange;
}
//---------------------------------------------------------------------------
// Method for constructing all live ranges in a function. It creates live
// ranges for all values defined in the instruction stream. Also, it
// creates live ranges for all incoming arguments of the function.
//---------------------------------------------------------------------------
void LiveRangeInfo::constructLiveRanges() {
if (DEBUG_RA >= RA_DEBUG_LiveRanges)
cerr << "Constructing Live Ranges ...\n";
// first find the live ranges for all incoming args of the function since
// those LRs start from the start of the function
for (Function::const_aiterator AI = Meth->abegin(); AI != Meth->aend(); ++AI)
createNewLiveRange(AI, /*isCC*/ false);
// Now suggest hardware registers for these function args
MRI.suggestRegs4MethodArgs(Meth, *this);
// Now create LRs for machine instructions. A new LR will be created
// only for defs in the machine instr since, we assume that all Values are
// defined before they are used. However, there can be multiple defs for
// the same Value in machine instructions.
//
// Also, find CALL and RETURN instructions, which need extra work.
//
MachineFunction &MF = MachineFunction::get(Meth);
for (MachineFunction::iterator BBI = MF.begin(); BBI != MF.end(); ++BBI) {
MachineBasicBlock &MBB = *BBI;
// iterate over all the machine instructions in BB
for(MachineBasicBlock::iterator MInstIterator = MBB.begin();
MInstIterator != MBB.end(); ++MInstIterator) {
MachineInstr *MInst = *MInstIterator;
// If the machine instruction is a call/return instruction, add it to
// CallRetInstrList for processing its args, ret value, and ret addr.
//
if(TM.getInstrInfo().isReturn(MInst->getOpCode()) ||
TM.getInstrInfo().isCall(MInst->getOpCode()))
CallRetInstrList.push_back(MInst);
// iterate over explicit MI operands and create a new LR
// for each operand that is defined by the instruction
for (MachineInstr::val_op_iterator OpI = MInst->begin(),
OpE = MInst->end(); OpI != OpE; ++OpI)
if (OpI.isDefOnly() || OpI.isDefAndUse()) {
const Value *Def = *OpI;
bool isCC = (OpI.getMachineOperand().getType()
== MachineOperand::MO_CCRegister);
LiveRange* LR = createOrAddToLiveRange(Def, isCC);
// If the operand has a pre-assigned register,
// set it directly in the LiveRange
if (OpI.getMachineOperand().hasAllocatedReg()) {
unsigned getClassId;
LR->setColor(MRI.getClassRegNum(
OpI.getMachineOperand().getAllocatedRegNum(),
getClassId));
}
}
// iterate over implicit MI operands and create a new LR
// for each operand that is defined by the instruction
for (unsigned i = 0; i < MInst->getNumImplicitRefs(); ++i)
if (MInst->getImplicitOp(i).opIsDefOnly() ||
MInst->getImplicitOp(i).opIsDefAndUse()) {
const Value *Def = MInst->getImplicitRef(i);
LiveRange* LR = createOrAddToLiveRange(Def, /*isCC*/ false);
// If the implicit operand has a pre-assigned register,
// set it directly in the LiveRange
if (MInst->getImplicitOp(i).hasAllocatedReg()) {
unsigned getClassId;
LR->setColor(MRI.getClassRegNum(
MInst->getImplicitOp(i).getAllocatedRegNum(),
getClassId));
}
}
} // for all machine instructions in the BB
} // for all BBs in function
// Now we have to suggest clors for call and return arg live ranges.
// Also, if there are implicit defs (e.g., retun value of a call inst)
// they must be added to the live range list
//
suggestRegs4CallRets();
if( DEBUG_RA >= RA_DEBUG_LiveRanges)
cerr << "Initial Live Ranges constructed!\n";
}
//---------------------------------------------------------------------------
// If some live ranges must be colored with specific hardware registers
// (e.g., for outgoing call args), suggesting of colors for such live
// ranges is done using target specific function. Those functions are called
// from this function. The target specific methods must:
// 1) suggest colors for call and return args.
// 2) create new LRs for implicit defs in machine instructions
//---------------------------------------------------------------------------
void LiveRangeInfo::suggestRegs4CallRets() {
std::vector<MachineInstr*>::iterator It = CallRetInstrList.begin();
for( ; It != CallRetInstrList.end(); ++It) {
MachineInstr *MInst = *It;
MachineOpCode OpCode = MInst->getOpCode();
if ((TM.getInstrInfo()).isReturn(OpCode))
MRI.suggestReg4RetValue(MInst, *this);
else if ((TM.getInstrInfo()).isCall(OpCode))
MRI.suggestRegs4CallArgs(MInst, *this);
else
assert( 0 && "Non call/ret instr in CallRetInstrList" );
}
}
//--------------------------------------------------------------------------
// The following method coalesces live ranges when possible. This method
// must be called after the interference graph has been constructed.
/* Algorithm:
for each BB in function
for each machine instruction (inst)
for each definition (def) in inst
for each operand (op) of inst that is a use
if the def and op are of the same register type
if the def and op do not interfere //i.e., not simultaneously live
if (degree(LR of def) + degree(LR of op)) <= # avail regs
if both LRs do not have suggested colors
merge2IGNodes(def, op) // i.e., merge 2 LRs
*/
//---------------------------------------------------------------------------
// Checks if live range LR interferes with any node assigned or suggested to
// be assigned the specified color
//
inline bool InterferesWithColor(const LiveRange& LR, unsigned color)
{
IGNode* lrNode = LR.getUserIGNode();
for (unsigned n=0, NN = lrNode->getNumOfNeighbors(); n < NN; n++) {
LiveRange *neighLR = lrNode->getAdjIGNode(n)->getParentLR();
if (neighLR->hasColor() && neighLR->getColor() == color)
return true;
if (neighLR->hasSuggestedColor() && neighLR->getSuggestedColor() == color)
return true;
}
return false;
}
// Cannot coalesce if any of the following is true:
// (1) Both LRs have suggested colors (should be "different suggested colors"?)
// (2) Both LR1 and LR2 have colors and the colors are different
// (but if the colors are the same, it is definitely safe to coalesce)
// (3) LR1 has color and LR2 interferes with any LR that has the same color
// (4) LR2 has color and LR1 interferes with any LR that has the same color
//
inline bool InterfsPreventCoalescing(const LiveRange& LROfDef,
const LiveRange& LROfUse)
{
// (4) if they have different suggested colors, cannot coalesce
if (LROfDef.hasSuggestedColor() && LROfUse.hasSuggestedColor())
return true;
// if neither has a color, nothing more to do.
if (! LROfDef.hasColor() && ! LROfUse.hasColor())
return false;
// (2, 3) if L1 has color...
if (LROfDef.hasColor()) {
if (LROfUse.hasColor())
return (LROfUse.getColor() != LROfDef.getColor());
return InterferesWithColor(LROfUse, LROfDef.getColor());
}
// (4) else only LROfUse has a color: check if that could interfere
return InterferesWithColor(LROfDef, LROfUse.getColor());
}
void LiveRangeInfo::coalesceLRs()
{
if(DEBUG_RA >= RA_DEBUG_LiveRanges)
cerr << "\nCoalescing LRs ...\n";
MachineFunction &MF = MachineFunction::get(Meth);
for (MachineFunction::iterator BBI = MF.begin(); BBI != MF.end(); ++BBI) {
MachineBasicBlock &MBB = *BBI;
// iterate over all the machine instructions in BB
for(MachineBasicBlock::iterator MII = MBB.begin(); MII != MBB.end(); ++MII){
const MachineInstr *MI = *MII;
if( DEBUG_RA >= RA_DEBUG_LiveRanges) {
cerr << " *Iterating over machine instr ";
MI->dump();
cerr << "\n";
}
// iterate over MI operands to find defs
for(MachineInstr::const_val_op_iterator DefI = MI->begin(),
DefE = MI->end(); DefI != DefE; ++DefI) {
if (DefI.isDefOnly() || DefI.isDefAndUse()) { // this operand is modified
LiveRange *LROfDef = getLiveRangeForValue( *DefI );
RegClass *RCOfDef = LROfDef->getRegClass();
MachineInstr::const_val_op_iterator UseI = MI->begin(),
UseE = MI->end();
for( ; UseI != UseE; ++UseI) { // for all uses
LiveRange *LROfUse = getLiveRangeForValue( *UseI );
if (!LROfUse) { // if LR of use is not found
//don't warn about labels
if (!isa<BasicBlock>(*UseI) && DEBUG_RA >= RA_DEBUG_LiveRanges)
cerr << " !! Warning: No LR for use " << RAV(*UseI) << "\n";
continue; // ignore and continue
}
if (LROfUse == LROfDef) // nothing to merge if they are same
continue;
if (MRI.getRegType(LROfDef) == MRI.getRegType(LROfUse)) {
// If the two RegTypes are the same
if (!RCOfDef->getInterference(LROfDef, LROfUse) ) {
unsigned CombinedDegree =
LROfDef->getUserIGNode()->getNumOfNeighbors() +
LROfUse->getUserIGNode()->getNumOfNeighbors();
if (CombinedDegree > RCOfDef->getNumOfAvailRegs()) {
// get more precise estimate of combined degree
CombinedDegree = LROfDef->getUserIGNode()->
getCombinedDegree(LROfUse->getUserIGNode());
}
if (CombinedDegree <= RCOfDef->getNumOfAvailRegs()) {
// if both LRs do not have different pre-assigned colors
// and both LRs do not have suggested colors
if (! InterfsPreventCoalescing(*LROfDef, *LROfUse)) {
RCOfDef->mergeIGNodesOfLRs(LROfDef, LROfUse);
unionAndUpdateLRs(LROfDef, LROfUse);
}
} // if combined degree is less than # of regs
} // if def and use do not interfere
}// if reg classes are the same
} // for all uses
} // if def
} // for all defs
} // for all machine instructions
} // for all BBs
if (DEBUG_RA >= RA_DEBUG_LiveRanges)
cerr << "\nCoalescing Done!\n";
}
/*--------------------------- Debug code for printing ---------------*/
void LiveRangeInfo::printLiveRanges() {
LiveRangeMapType::iterator HMI = LiveRangeMap.begin(); // hash map iterator
cerr << "\nPrinting Live Ranges from Hash Map:\n";
for( ; HMI != LiveRangeMap.end(); ++HMI) {
if (HMI->first && HMI->second) {
cerr << " Value* " << RAV(HMI->first) << "\t: ";
if (IGNode* igNode = HMI->second->getUserIGNode())
cerr << "LR# " << igNode->getIndex();
else
cerr << "LR# " << "<no-IGNode>";
cerr << "\t:Values = "; printSet(*HMI->second); cerr << "\n";
}
}
}
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