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Use a new VRegPHIUseCount to compute uses of PHI values by other phi values

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in the basic block being processed.  This fixes PhiElimination on kimwitu++
from taking 105s to taking a much more reasonable 0.6s (in a debug build).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13453 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-05-10 19:06:37 +00:00
parent 791f896d9f
commit 80e20eb487
1 changed files with 21 additions and 14 deletions
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35
lib/CodeGen/PHIElimination.cpp
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@ -68,12 +68,21 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) {
const TargetInstrInfo &MII = MF.getTarget().getInstrInfo();
const MRegisterInfo *RegInfo = MF.getTarget().getRegisterInfo();
// VRegPHIUseCount - Keep track of the number of times each virtual register
// is used by PHI nodes in this block.
std::map<unsigned, unsigned> VRegPHIUseCount;
// Get an iterator to the first instruction after the last PHI node (this may
// allso be the end of the basic block).
// allso be the end of the basic block). While we are scanning the PHIs,
// populate the VRegPHIUseCount map.
MachineBasicBlock::iterator AfterPHIsIt = MBB.begin();
while (AfterPHIsIt != MBB.end() &&
AfterPHIsIt->getOpcode() == TargetInstrInfo::PHI)
AfterPHIsIt->getOpcode() == TargetInstrInfo::PHI) {
MachineInstr *PHI = AfterPHIsIt;
for (unsigned i = 1, e = PHI->getNumOperands(); i < e; i += 2)
VRegPHIUseCount[PHI->getOperand(i).getReg()]++;
++AfterPHIsIt; // Skip over all of the PHI nodes...
}
while (MBB.front().getOpcode() == TargetInstrInfo::PHI) {
// Unlink the PHI node from the basic block... but don't delete the PHI yet
@ -134,6 +143,11 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) {
}
}
// Adjust the VRegPHIUseCount map to account for the removal of this PHI
// node.
for (unsigned i = 1; i != MI->getNumOperands(); i += 2)
VRegPHIUseCount[MI->getOperand(i).getReg()]--;
// Now loop over all of the incoming arguments, changing them to copy into
// the IncomingReg register in the corresponding predecessor basic block.
//
@ -217,18 +231,11 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) {
}
// Is it used by any PHI instructions in this block?
if (ValueIsLive) break;
// Loop over all of the PHIs in this successor, checking to see if
// the register is being used...
for (MachineBasicBlock::iterator BBI = MBB->begin(), E=MBB->end();
BBI != E && BBI->getOpcode() == TargetInstrInfo::PHI;
++BBI)
for (unsigned i = 1, e = BBI->getNumOperands(); i < e; i += 2)
if (BBI->getOperand(i).getReg() == SrcReg) {
ValueIsLive = true;
break;
}
if (!ValueIsLive) {
std::map<unsigned,unsigned>::iterator I =
VRegPHIUseCount.find(SrcReg);
ValueIsLive = I != VRegPHIUseCount.end() && I->second;
}
}
// Okay, if we now know that the value is not live out of the block,