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Refactoring: Extract method PHIElimination::isLiveOut().

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Clean up some whitespace.
No functional changes.

llvm-svn: 86724
This commit is contained in:
Jakob Stoklund Olesen 2009-11-10 22:00:56 +00:00
parent f48b199c43
commit 35918309f2
2 changed files with 64 additions and 68 deletions
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126
lib/CodeGen/PHIElimination.cpp
View File

@ -155,7 +155,7 @@ llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB,
/// under the assuption that it needs to be lowered in a way that supports
/// atomic execution of PHIs. This lowering method is always correct all of the
/// time.
///
///
void llvm::PHIElimination::LowerAtomicPHINode(
MachineBasicBlock &MBB,
MachineBasicBlock::iterator AfterPHIsIt) {
@ -186,7 +186,7 @@ void llvm::PHIElimination::LowerAtomicPHINode(
}
// Record PHI def.
assert(!hasPHIDef(DestReg) && "Vreg has multiple phi-defs?");
assert(!hasPHIDef(DestReg) && "Vreg has multiple phi-defs?");
PHIDefs[DestReg] = &MBB;
// Update live variable information if there is any.
@ -250,7 +250,7 @@ void llvm::PHIElimination::LowerAtomicPHINode(
// basic block.
if (!MBBsInsertedInto.insert(&opBlock))
continue; // If the copy has already been emitted, we're done.
// Find a safe location to insert the copy, this may be the first terminator
// in the block (or end()).
MachineBasicBlock::iterator InsertPos = FindCopyInsertPoint(opBlock, SrcReg);
@ -260,82 +260,24 @@ void llvm::PHIElimination::LowerAtomicPHINode(
// Now update live variable information if we have it. Otherwise we're done
if (!LV) continue;
// We want to be able to insert a kill of the register if this PHI (aka, the
// copy we just inserted) is the last use of the source value. Live
// variable analysis conservatively handles this by saying that the value is
// live until the end of the block the PHI entry lives in. If the value
// really is dead at the PHI copy, there will be no successor blocks which
// have the value live-in.
//
// Check to see if the copy is the last use, and if so, update the live
// variables information so that it knows the copy source instruction kills
// the incoming value.
LiveVariables::VarInfo &InRegVI = LV->getVarInfo(SrcReg);
// Loop over all of the successors of the basic block, checking to see if
// the value is either live in the block, or if it is killed in the block.
// Also check to see if this register is in use by another PHI node which
// has not yet been eliminated. If so, it will be killed at an appropriate
// point later.
// Is it used by any PHI instructions in this block?
bool ValueIsLive = VRegPHIUseCount[BBVRegPair(&opBlock, SrcReg)] != 0;
std::vector<MachineBasicBlock*> OpSuccBlocks;
// Otherwise, scan successors, including the BB the PHI node lives in.
for (MachineBasicBlock::succ_iterator SI = opBlock.succ_begin(),
E = opBlock.succ_end(); SI != E && !ValueIsLive; ++SI) {
MachineBasicBlock *SuccMBB = *SI;
// Is it alive in this successor?
unsigned SuccIdx = SuccMBB->getNumber();
if (InRegVI.AliveBlocks.test(SuccIdx)) {
ValueIsLive = true;
break;
}
OpSuccBlocks.push_back(SuccMBB);
}
// Check to see if this value is live because there is a use in a successor
// that kills it.
if (!ValueIsLive) {
switch (OpSuccBlocks.size()) {
case 1: {
MachineBasicBlock *MBB = OpSuccBlocks[0];
for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i)
if (InRegVI.Kills[i]->getParent() == MBB) {
ValueIsLive = true;
break;
}
break;
}
case 2: {
MachineBasicBlock *MBB1 = OpSuccBlocks[0], *MBB2 = OpSuccBlocks[1];
for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i)
if (InRegVI.Kills[i]->getParent() == MBB1 ||
InRegVI.Kills[i]->getParent() == MBB2) {
ValueIsLive = true;
break;
}
break;
}
default:
std::sort(OpSuccBlocks.begin(), OpSuccBlocks.end());
for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i)
if (std::binary_search(OpSuccBlocks.begin(), OpSuccBlocks.end(),
InRegVI.Kills[i]->getParent())) {
ValueIsLive = true;
break;
}
}
}
bool ValueIsUsed = VRegPHIUseCount[BBVRegPair(&opBlock, SrcReg)] != 0;
// Okay, if we now know that the value is not live out of the block, we can
// add a kill marker in this block saying that it kills the incoming value!
if (!ValueIsLive) {
if (!ValueIsUsed && !isLiveOut(SrcReg, opBlock, *LV)) {
// In our final twist, we have to decide which instruction kills the
// register. In most cases this is the copy, however, the first
// terminator instruction at the end of the block may also use the value.
@ -346,7 +288,7 @@ void llvm::PHIElimination::LowerAtomicPHINode(
if (Term != opBlock.end()) {
if (Term->readsRegister(SrcReg))
KillInst = Term;
// Check that no other terminators use values.
#ifndef NDEBUG
for (MachineBasicBlock::iterator TI = next(Term); TI != opBlock.end();
@ -357,16 +299,16 @@ void llvm::PHIElimination::LowerAtomicPHINode(
}
#endif
}
// Finally, mark it killed.
LV->addVirtualRegisterKilled(SrcReg, KillInst);
// This vreg no longer lives all of the way through opBlock.
unsigned opBlockNum = opBlock.getNumber();
InRegVI.AliveBlocks.reset(opBlockNum);
LV->getVarInfo(SrcReg).AliveBlocks.reset(opBlockNum);
}
}
// Really delete the PHI instruction now!
MF.DeleteMachineInstr(MPhi);
++NumAtomic;
@ -386,3 +328,51 @@ void llvm::PHIElimination::analyzePHINodes(const MachineFunction& Fn) {
++VRegPHIUseCount[BBVRegPair(BBI->getOperand(i + 1).getMBB(),
BBI->getOperand(i).getReg())];
}
bool llvm::PHIElimination::isLiveOut(unsigned Reg, const MachineBasicBlock &MBB,
LiveVariables &LV) {
LiveVariables::VarInfo &InRegVI = LV.getVarInfo(Reg);
// Loop over all of the successors of the basic block, checking to see if
// the value is either live in the block, or if it is killed in the block.
std::vector<MachineBasicBlock*> OpSuccBlocks;
// Otherwise, scan successors, including the BB the PHI node lives in.
for (MachineBasicBlock::const_succ_iterator SI = MBB.succ_begin(),
E = MBB.succ_end(); SI != E; ++SI) {
MachineBasicBlock *SuccMBB = *SI;
// Is it alive in this successor?
unsigned SuccIdx = SuccMBB->getNumber();
if (InRegVI.AliveBlocks.test(SuccIdx))
return true;
OpSuccBlocks.push_back(SuccMBB);
}
// Check to see if this value is live because there is a use in a successor
// that kills it.
switch (OpSuccBlocks.size()) {
case 1: {
MachineBasicBlock *SuccMBB = OpSuccBlocks[0];
for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i)
if (InRegVI.Kills[i]->getParent() == SuccMBB)
return true;
break;
}
case 2: {
MachineBasicBlock *SuccMBB1 = OpSuccBlocks[0], *SuccMBB2 = OpSuccBlocks[1];
for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i)
if (InRegVI.Kills[i]->getParent() == SuccMBB1 ||
InRegVI.Kills[i]->getParent() == SuccMBB2)
return true;
break;
}
default:
std::sort(OpSuccBlocks.begin(), OpSuccBlocks.end());
for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i)
if (std::binary_search(OpSuccBlocks.begin(), OpSuccBlocks.end(),
InRegVI.Kills[i]->getParent()))
return true;
}
return false;
}

6
lib/CodeGen/PHIElimination.h
View File

@ -89,6 +89,12 @@ namespace llvm {
///
void analyzePHINodes(const MachineFunction& Fn);
/// isLiveOut - Determine if Reg is live out from MBB, when not
/// considering PHI nodes. This means that Reg is either killed by
/// a successor block or passed through one.
bool isLiveOut(unsigned Reg, const MachineBasicBlock &MBB,
LiveVariables &LV);
// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
// SrcReg. This needs to be after any def or uses of SrcReg, but before
// any subsequent point where control flow might jump out of the basic