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Fix N^2 algorithm

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6112 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2003-05-12 04:08:54 +00:00
parent 12ba6fd61f
commit 98719d7cdc
1 changed files with 34 additions and 25 deletions
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59
lib/CodeGen/PHIElimination.cpp
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@ -122,41 +122,50 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) {
// source path the PHI. // source path the PHI.
MachineBasicBlock &opBlock = *MI->getOperand(i).getMachineBasicBlock(); MachineBasicBlock &opBlock = *MI->getOperand(i).getMachineBasicBlock();
// Figure out where to insert the copy, which is at the end of the
// predecessor basic block, but before any terminator/branch
// instructions...
MachineBasicBlock::iterator I = opBlock.end();
if (I != opBlock.begin()) { // Handle empty blocks
--I;
// must backtrack over ALL the branches in the previous block
while (MII.isTerminatorInstr((*I)->getOpcode()) &&
I != opBlock.begin())
--I;
// move back to the first branch instruction so new instructions
// are inserted right in front of it and not in front of a non-branch
if (!MII.isTerminatorInstr((*I)->getOpcode()))
++I;
}
// Check to make sure we haven't already emitted the copy for this block. // Check to make sure we haven't already emitted the copy for this block.
// This can happen because PHI nodes may have multiple entries for the // This can happen because PHI nodes may have multiple entries for the
// same basic block. It doesn't matter which entry we use though, because // same basic block. It doesn't matter which entry we use though, because
// all incoming values are guaranteed to be the same for a particular bb. // all incoming values are guaranteed to be the same for a particular bb.
// //
// Note that this is N^2 in the number of phi node entries, but since the // If we emitted a copy for this basic block already, it will be right
// # of entries is usually small, this is not a problem. FIXME: this // where we want to insert one now. Just check for a definition of the
// should just check to see if there is already a copy in the bottom of // register we are interested in!
// this basic block!
// //
bool HaveNotEmitted = true; bool HaveNotEmitted = true;
for (int op = MI->getNumOperands() - 1; op != i; op -= 2)
if (&opBlock == MI->getOperand(op).getMachineBasicBlock()) { if (I != opBlock.begin()) {
HaveNotEmitted = false; MachineInstr *PrevInst = *(I-1);
break; for (unsigned i = 0, e = PrevInst->getNumOperands(); i != e; ++i) {
MachineOperand &MO = PrevInst->getOperand(i);
if (MO.isVirtualRegister() && MO.getReg() == IncomingReg)
if (MO.opIsDef() || MO.opIsDefAndUse()) {
HaveNotEmitted = false;
break;
}
} }
}
if (HaveNotEmitted) { if (HaveNotEmitted) {
MachineBasicBlock::iterator I = opBlock.end(); assert(opVal.isVirtualRegister() &&
if (I != opBlock.begin()) { // Handle empty blocks "Machine PHI Operands must all be virtual registers!");
--I; RegInfo->copyRegToReg(opBlock, I, IncomingReg, opVal.getReg(), RC);
// must backtrack over ALL the branches in the previous block
while (MII.isTerminatorInstr((*I)->getOpcode()) &&
I != opBlock.begin())
--I;
// move back to the first branch instruction so new instructions
// are inserted right in front of it and not in front of a non-branch
if (!MII.isTerminatorInstr((*I)->getOpcode()))
++I;
}
assert(opVal.isVirtualRegister() &&
"Machine PHI Operands must all be virtual registers!");
RegInfo->copyRegToReg(opBlock, I, IncomingReg, opVal.getReg(), RC);
} }
} }