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Fix for PR929. The PHI nodes were being gone through for each instruction

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in a successor block for every block...resulting in some O(N^k) algorithm
which wasn't very good for performance. Calculating this information up
front and keeping it in a map made it much faster.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30697 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling
2006-10-03 07:20:20 +00:00
parent 86f7b2100c
commit f7da4e939f
2 changed files with 36 additions and 21 deletions
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45
lib/CodeGen/LiveVariables.cpp
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@@ -92,7 +92,6 @@ bool LiveVariables::RegisterDefIsDead(MachineInstr *MI, unsigned Reg) const {
return std::binary_search(I->second.begin(), I->second.end(), Reg);
}
void LiveVariables::MarkVirtRegAliveInBlock(VarInfo &VRInfo,
MachineBasicBlock *MBB) {
unsigned BBNum = MBB->getNumber();
@@ -212,6 +211,8 @@ bool LiveVariables::runOnMachineFunction(MachineFunction &MF) {
HandlePhysRegDef(I->first, 0);
}
analyzePHINodes(MF);
// Calculate live variable information in depth first order on the CFG of the
// function. This guarantees that we will see the definition of a virtual
// register before its uses due to dominance properties of SSA (except for PHI
@@ -288,26 +289,16 @@ bool LiveVariables::runOnMachineFunction(MachineFunction &MF) {
// bottom of this basic block. We check all of our successor blocks to see
// if they have PHI nodes, and if so, we simulate an assignment at the end
// of the current block.
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
E = MBB->succ_end(); SI != E; ++SI) {
MachineBasicBlock *Succ = *SI;
if (!PHIVarInfo[MBB].empty()) {
std::vector<unsigned>& VarInfoVec = PHIVarInfo[MBB];
// PHI nodes are guaranteed to be at the top of the block...
for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
MI != ME && MI->getOpcode() == TargetInstrInfo::PHI; ++MI) {
for (unsigned i = 1; ; i += 2) {
assert(MI->getNumOperands() > i+1 &&
"Didn't find an entry for our predecessor??");
if (MI->getOperand(i+1).getMachineBasicBlock() == MBB) {
MachineOperand &MO = MI->getOperand(i);
VarInfo &VRInfo = getVarInfo(MO.getReg());
assert(VRInfo.DefInst && "Register use before def (or no def)!");
for (std::vector<unsigned>::iterator I = VarInfoVec.begin(),
E = VarInfoVec.end(); I != E; ++I) {
VarInfo& VRInfo = getVarInfo(*I);
assert(VRInfo.DefInst && "Register use before def (or no def)!");
// Only mark it alive only in the block we are representing.
MarkVirtRegAliveInBlock(VRInfo, MBB);
break; // Found the PHI entry for this block.
}
}
// Only mark it alive only in the block we are representing.
MarkVirtRegAliveInBlock(VRInfo, MBB);
}
}
@@ -362,6 +353,7 @@ bool LiveVariables::runOnMachineFunction(MachineFunction &MF) {
assert(Visited.count(&*i) != 0 && "unreachable basic block found");
#endif
PHIVarInfo.clear();
return false;
}
@@ -450,4 +442,17 @@ void LiveVariables::removeVirtualRegistersDead(MachineInstr *MI) {
RegistersDead.erase(I);
}
/// analyzePHINodes - Gather information about the PHI nodes in here. In
/// particular, we want to map the variable information of a virtual
/// register which is used in a PHI node. We map that to the BB the vreg is
/// coming from.
///
void LiveVariables::analyzePHINodes(const MachineFunction& Fn) {
for (MachineFunction::const_iterator I = Fn.begin(), E = Fn.end();
I != E; ++I)
for (MachineBasicBlock::const_iterator BBI = I->begin(), BBE = I->end();
BBI != BBE && BBI->getOpcode() == TargetInstrInfo::PHI; ++BBI)
for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
PHIVarInfo[BBI->getOperand(i + 1).getMachineBasicBlock()].
push_back(BBI->getOperand(i).getReg());
}