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Teach branch folding to fold identical jump tables together and to delete

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jump tables that are dead.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31273 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-10-28 18:34:47 +00:00
parent c4aacac056
commit 6acfe12dd6
1 changed files with 53 additions and 5 deletions
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58
lib/CodeGen/BranchFolding.cpp
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@ -98,6 +98,53 @@ bool BranchFolder::runOnMachineFunction(MachineFunction &MF) {
EverMadeChange |= MadeChangeThisIteration;
}
// See if any jump tables have become mergable or dead as the code generator
// did its thing.
MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
const std::vector<MachineJumpTableEntry> &JTs = JTI->getJumpTables();
if (!JTs.empty()) {
// Figure out how these jump tables should be merged.
std::vector<unsigned> JTMapping;
JTMapping.reserve(JTs.size());
// We always keep the 0th jump table.
JTMapping.push_back(0);
// Scan the jump tables, seeing if there are any duplicates. Note that this
// is N^2, which should be fixed someday.
for (unsigned i = 1, e = JTs.size(); i != e; ++i)
JTMapping.push_back(JTI->getJumpTableIndex(JTs[i].MBBs));
// If a jump table was merge with another one, walk the function rewriting
// references to jump tables to reference the new JT ID's. Keep track of
// whether we see a jump table idx, if not, we can delete the JT.
std::vector<bool> JTIsLive;
JTIsLive.resize(JTs.size());
for (MachineFunction::iterator BB = MF.begin(), E = MF.end();
BB != E; ++BB) {
for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
I != E; ++I)
for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) {
MachineOperand &Op = I->getOperand(op);
if (!Op.isJumpTableIndex()) continue;
unsigned NewIdx = JTMapping[Op.getJumpTableIndex()];
Op.setJumpTableIndex(NewIdx);
// Remember that this JT is live.
JTIsLive[NewIdx] = true;
}
}
// Finally, remove dead jump tables. This happens either because the
// indirect jump was unreachable (and thus deleted) or because the jump
// table was merged with some other one.
for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i)
if (!JTIsLive[i]) {
JTI->RemoveJumpTable(i);
EverMadeChange = true;
}
}
return EverMadeChange;
}
@ -444,8 +491,8 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
// If MBB was the target of a jump table, update jump tables to go to the
// fallthrough instead.
MBB->getParent()->getJumpTableInfo()->ReplaceMBBInJumpTables(MBB,
FallThrough);
MBB->getParent()->getJumpTableInfo()->
ReplaceMBBInJumpTables(MBB, FallThrough);
MadeChange = true;
}
return;
@ -543,7 +590,8 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) &&
PriorTBB != MBB && PriorFBB != MBB) {
if (PriorTBB == 0) {
assert(PriorCond.empty() && PriorFBB == 0 && "Bad branch analysis");
assert(PriorCond.empty() && PriorFBB == 0 &&
"Bad branch analysis");
PriorTBB = MBB;
} else {
assert(PriorFBB == 0 && "Machine CFG out of date!");
@ -569,8 +617,8 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
}
// Change any jumptables to go to the new MBB.
MBB->getParent()->getJumpTableInfo()->ReplaceMBBInJumpTables(MBB,
CurTBB);
MBB->getParent()->getJumpTableInfo()->
ReplaceMBBInJumpTables(MBB, CurTBB);
if (DidChange) {
++NumBranchOpts;
MadeChange = true;