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Run LiveVariables instead of computing liveness locally in -regalloc=fast.

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This actually makes everything slower, but the plan is to have isel add <kill>
flags the way it is already adding <dead> flags. Then LiveVariables can be
removed again.

When ignoring the time spent in LiveVariables, -regalloc=fast is now twice as
fast as -regalloc=local.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102034 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2010-04-21 23:18:07 +00:00
parent e3dd8550c6
commit a063e19593
1 changed files with 2 additions and 177 deletions
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179
lib/CodeGen/RegAllocFast.cpp
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@ -18,6 +18,7 @@
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/Target/TargetInstrInfo.h"
@ -123,6 +124,7 @@ namespace {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<LiveVariables>();
AU.addRequiredID(PHIEliminationID);
AU.addRequiredID(TwoAddressInstructionPassID);
MachineFunctionPass::getAnalysisUsage(AU);
@ -218,10 +220,6 @@ namespace {
unsigned OpNum, SmallSet<unsigned, 4> &RRegs,
unsigned PhysReg);
/// ComputeLocalLiveness - Computes liveness of registers within a basic
/// block, setting the killed/dead flags as appropriate.
void ComputeLocalLiveness(MachineBasicBlock& MBB);
void reloadPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned PhysReg);
};
@ -538,177 +536,6 @@ static bool isReadModWriteImplicitDef(MachineInstr *MI, unsigned Reg) {
return false;
}
// precedes - Helper function to determine with MachineInstr A
// precedes MachineInstr B within the same MBB.
static bool precedes(MachineBasicBlock::iterator A,
MachineBasicBlock::iterator B) {
if (A == B)
return false;
MachineBasicBlock::iterator I = A->getParent()->begin();
while (I != A->getParent()->end()) {
if (I == A)
return true;
else if (I == B)
return false;
++I;
}
return false;
}
/// ComputeLocalLiveness - Computes liveness of registers within a basic
/// block, setting the killed/dead flags as appropriate.
void RAFast::ComputeLocalLiveness(MachineBasicBlock& MBB) {
MachineRegisterInfo &MRI = MBB.getParent()->getRegInfo();
// Keep track of the most recently seen previous use or def of each reg,
// so that we can update them with dead/kill markers.
DenseMap<unsigned, std::pair<MachineInstr*, unsigned> > LastUseDef;
for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
I != E; ++I) {
if (I->isDebugValue())
continue;
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
MachineOperand &MO = I->getOperand(i);
// Uses don't trigger any flags, but we need to save
// them for later. Also, we have to process these
// _before_ processing the defs, since an instr
// uses regs before it defs them.
if (!MO.isReg() || !MO.getReg() || !MO.isUse())
continue;
LastUseDef[MO.getReg()] = std::make_pair(I, i);
if (TargetRegisterInfo::isVirtualRegister(MO.getReg())) continue;
const unsigned *Aliases = TRI->getAliasSet(MO.getReg());
if (Aliases == 0)
continue;
while (*Aliases) {
DenseMap<unsigned, std::pair<MachineInstr*, unsigned> >::iterator
alias = LastUseDef.find(*Aliases);
if (alias != LastUseDef.end() && alias->second.first != I)
LastUseDef[*Aliases] = std::make_pair(I, i);
++Aliases;
}
}
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
MachineOperand &MO = I->getOperand(i);
// Defs others than 2-addr redefs _do_ trigger flag changes:
// - A def followed by a def is dead
// - A use followed by a def is a kill
if (!MO.isReg() || !MO.getReg() || !MO.isDef()) continue;
DenseMap<unsigned, std::pair<MachineInstr*, unsigned> >::iterator
last = LastUseDef.find(MO.getReg());
if (last != LastUseDef.end()) {
// Check if this is a two address instruction. If so, then
// the def does not kill the use.
if (last->second.first == I &&
I->isRegTiedToUseOperand(i))
continue;
MachineOperand &lastUD =
last->second.first->getOperand(last->second.second);
if (lastUD.isDef())
lastUD.setIsDead(true);
else
lastUD.setIsKill(true);
}
LastUseDef[MO.getReg()] = std::make_pair(I, i);
}
}
// Live-out (of the function) registers contain return values of the function,
// so we need to make sure they are alive at return time.
MachineBasicBlock::iterator Ret = MBB.getFirstTerminator();
bool BBEndsInReturn = (Ret != MBB.end() && Ret->getDesc().isReturn());
if (BBEndsInReturn)
for (MachineRegisterInfo::liveout_iterator
I = MF->getRegInfo().liveout_begin(),
E = MF->getRegInfo().liveout_end(); I != E; ++I)
if (!Ret->readsRegister(*I)) {
Ret->addOperand(MachineOperand::CreateReg(*I, false, true));
LastUseDef[*I] = std::make_pair(Ret, Ret->getNumOperands()-1);
}
// Finally, loop over the final use/def of each reg
// in the block and determine if it is dead.
for (DenseMap<unsigned, std::pair<MachineInstr*, unsigned> >::iterator
I = LastUseDef.begin(), E = LastUseDef.end(); I != E; ++I) {
MachineInstr *MI = I->second.first;
unsigned idx = I->second.second;
MachineOperand &MO = MI->getOperand(idx);
bool isPhysReg = TargetRegisterInfo::isPhysicalRegister(MO.getReg());
// A crude approximation of "live-out" calculation
bool usedOutsideBlock = isPhysReg ? false :
UsedInMultipleBlocks.test(MO.getReg() -
TargetRegisterInfo::FirstVirtualRegister);
// If the machine BB ends in a return instruction, then the value isn't used
// outside of the BB.
if (!isPhysReg && (!usedOutsideBlock || BBEndsInReturn)) {
// DBG_VALUE complicates this: if the only refs of a register outside
// this block are DBG_VALUE, we can't keep the reg live just for that,
// as it will cause the reg to be spilled at the end of this block when
// it wouldn't have been otherwise. Nullify the DBG_VALUEs when that
// happens.
bool UsedByDebugValueOnly = false;
for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()),
UE = MRI.reg_end(); UI != UE; ++UI) {
// Two cases:
// - used in another block
// - used in the same block before it is defined (loop)
if (UI->getParent() == &MBB &&
!(MO.isDef() && UI.getOperand().isUse() && precedes(&*UI, MI)))
continue;
if (UI->isDebugValue()) {
UsedByDebugValueOnly = true;
continue;
}
// A non-DBG_VALUE use means we can leave DBG_VALUE uses alone.
UsedInMultipleBlocks.set(MO.getReg() -
TargetRegisterInfo::FirstVirtualRegister);
usedOutsideBlock = true;
UsedByDebugValueOnly = false;
break;
}
if (UsedByDebugValueOnly)
for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()),
UE = MRI.reg_end(); UI != UE; ++UI)
if (UI->isDebugValue() &&
(UI->getParent() != &MBB ||
(MO.isDef() && precedes(&*UI, MI))))
UI.getOperand().setReg(0U);
}
// Physical registers and those that are not live-out of the block are
// killed/dead at their last use/def within this block.
if (isPhysReg || !usedOutsideBlock || BBEndsInReturn) {
if (MO.isUse()) {
// Don't mark uses that are tied to defs as kills.
if (!MI->isRegTiedToDefOperand(idx))
MO.setIsKill(true);
} else {
MO.setIsDead(true);
}
}
}
}
void RAFast::AllocateBasicBlock(MachineBasicBlock &MBB) {
// loop over each instruction
MachineBasicBlock::iterator MII = MBB.begin();
@ -733,8 +560,6 @@ void RAFast::AllocateBasicBlock(MachineBasicBlock &MBB) {
}
}
ComputeLocalLiveness(MBB);
// Otherwise, sequentially allocate each instruction in the MBB.
while (MII != MBB.end()) {
MachineInstr *MI = MII++;