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Calculate liveness on the fly for local registers.

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When working top-down in a basic block, substituting physregs for virtregs, the use-def chains are kept up to date. That means we can recognize a virtreg kill by the use-def chain becoming empty.

This makes the fast allocator independent of incoming kill flags.

llvm-svn: 103866
This commit is contained in:
Jakob Stoklund Olesen 2010-05-15 06:09:08 +00:00
parent 9c2a75e5e3
commit 671a452627
1 changed files with 31 additions and 0 deletions
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31
lib/CodeGen/RegAllocFast.cpp
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@ -132,6 +132,8 @@ namespace {
bool runOnMachineFunction(MachineFunction &Fn);
void AllocateBasicBlock(MachineBasicBlock &MBB);
int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC);
bool isLastUseOfLocalReg(MachineOperand&);
void addKillFlag(LiveRegMap::iterator i);
void killVirtReg(LiveRegMap::iterator i);
void killVirtReg(unsigned VirtReg);
@ -174,6 +176,26 @@ int RAFast::getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC) {
return FrameIdx;
}
/// isLastUseOfLocalReg - Return true if MO is the only remaining reference to
/// its virtual register, and it is guaranteed to be a block-local register.
///
bool RAFast::isLastUseOfLocalReg(MachineOperand &MO) {
// Check for non-debug uses or defs following MO.
// This is the most likely way to fail - fast path it.
MachineOperand *i = &MO;
while ((i = i->getNextOperandForReg()))
if (!i->isDebug())
return false;
// If the register has ever been spilled or reloaded, we conservatively assume
// it is a global register used in multiple blocks.
if (StackSlotForVirtReg[MO.getReg()] != -1)
return false;
// Check that the use/def chain has exactly one operand - MO.
return &MRI->reg_nodbg_begin(MO.getReg()).getOperand() == &MO;
}
/// addKillFlag - Set kill flags on last use of a virtual register.
void RAFast::addKillFlag(LiveRegMap::iterator lri) {
assert(lri != LiveVirtRegs.end() && "Killing unmapped virtual register");
@ -566,6 +588,15 @@ unsigned RAFast::reloadVirtReg(MachineBasicBlock &MBB, MachineInstr *MI,
TII->loadRegFromStackSlot(MBB, MI, lri->second.PhysReg, FrameIndex, RC,
TRI);
++NumLoads;
} else if (lri->second.Dirty) {
MachineOperand &MO = MI->getOperand(OpNum);
if (isLastUseOfLocalReg(MO)) {
DEBUG(dbgs() << "Killing last use: " << MO << "\n");
MO.setIsKill();
} else if (MO.isKill()) {
DEBUG(dbgs() << "Clearing dubious kill: " << MO << "\n");
MO.setIsKill(false);
}
}
LiveReg &LR = lri->second;
LR.LastUse = MI;