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Postra machine licm must add registers defined by loop invariants to *all* of

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the live-in sets of BBs in the loop. Otherwise later pass may end up using the
registers and override the invariant. rdar://7852937
No reasonablly sized test case possible.

llvm-svn: 101626
This commit is contained in:
Evan Cheng 2010-04-17 07:07:11 +00:00
parent 35e42e1c73
commit 0004496a98
1 changed files with 23 additions and 48 deletions
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71
lib/CodeGen/MachineLICM.cpp
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@ -109,7 +109,7 @@ namespace {
/// HoistRegionPostRA - Walk the specified region of the CFG and hoist loop
/// invariants out to the preheader.
void HoistRegionPostRA(MachineDomTreeNode *N);
void HoistRegionPostRA();
/// HoistPostRA - When an instruction is found to only use loop invariant
/// operands that is safe to hoist, this instruction is called to do the
@ -122,10 +122,9 @@ namespace {
SmallSet<int, 32> &StoredFIs,
SmallVector<CandidateInfo, 32> &Candidates);
/// AddToLiveIns - Add 'Reg' to the livein sets of BBs in the backedge path
/// from MBB to LoopHeader (inclusive).
void AddToLiveIns(unsigned Reg,
MachineBasicBlock *MBB, MachineBasicBlock *LoopHeader);
/// AddToLiveIns - Add register 'Reg' to the livein sets of BBs in the
/// current loop.
void AddToLiveIns(unsigned Reg);
/// IsLICMCandidate - Returns true if the instruction may be a suitable
/// candidate for LICM. e.g. If the instruction is a call, then it's obviously
@ -239,12 +238,12 @@ bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
if (!CurPreheader)
continue;
// CSEMap is initialized for loop header when the first instruction is
// being hoisted.
MachineDomTreeNode *N = DT->getNode(CurLoop->getHeader());
if (!PreRegAlloc)
HoistRegionPostRA(N);
HoistRegionPostRA();
else {
// CSEMap is initialized for loop header when the first instruction is
// being hoisted.
MachineDomTreeNode *N = DT->getNode(CurLoop->getHeader());
HoistRegion(N);
CSEMap.clear();
}
@ -349,9 +348,7 @@ void MachineLICM::ProcessMI(MachineInstr *MI,
/// HoistRegionPostRA - Walk the specified region of the CFG and hoist loop
/// invariants out to the preheader.
void MachineLICM::HoistRegionPostRA(MachineDomTreeNode *N) {
assert(N != 0 && "Null dominator tree node?");
void MachineLICM::HoistRegionPostRA() {
unsigned NumRegs = TRI->getNumRegs();
unsigned *PhysRegDefs = new unsigned[NumRegs];
std::fill(PhysRegDefs, PhysRegDefs + NumRegs, 0);
@ -360,15 +357,10 @@ void MachineLICM::HoistRegionPostRA(MachineDomTreeNode *N) {
SmallSet<int, 32> StoredFIs;
// Walk the entire region, count number of defs for each register, and
// return potential LICM candidates.
SmallVector<MachineDomTreeNode*, 8> WorkList;
WorkList.push_back(N);
do {
N = WorkList.pop_back_val();
MachineBasicBlock *BB = N->getBlock();
if (!CurLoop->contains(MLI->getLoopFor(BB)))
continue;
// collect potential LICM candidates.
const std::vector<MachineBasicBlock*> Blocks = CurLoop->getBlocks();
for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
MachineBasicBlock *BB = Blocks[i];
// Conservatively treat live-in's as an external def.
// FIXME: That means a reload that're reused in successor block(s) will not
// be LICM'ed.
@ -385,11 +377,7 @@ void MachineLICM::HoistRegionPostRA(MachineDomTreeNode *N) {
MachineInstr *MI = &*MII;
ProcessMI(MI, PhysRegDefs, StoredFIs, Candidates);
}
const std::vector<MachineDomTreeNode*> &Children = N->getChildren();
for (unsigned I = 0, E = Children.size(); I != E; ++I)
WorkList.push_back(Children[I]);
} while (!WorkList.empty());
}
// Now evaluate whether the potential candidates qualify.
// 1. Check if the candidate defined register is defined by another
@ -424,23 +412,11 @@ void MachineLICM::HoistRegionPostRA(MachineDomTreeNode *N) {
}
/// AddToLiveIns - Add register 'Reg' to the livein sets of BBs in the
/// backedge path from MBB to LoopHeader.
void MachineLICM::AddToLiveIns(unsigned Reg, MachineBasicBlock *MBB,
MachineBasicBlock *LoopHeader) {
SmallPtrSet<MachineBasicBlock*, 4> Visited;
SmallVector<MachineBasicBlock*, 4> WorkList;
WorkList.push_back(MBB);
do {
MBB = WorkList.pop_back_val();
if (!Visited.insert(MBB))
continue;
MBB->addLiveIn(Reg);
if (MBB == LoopHeader)
continue;
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
E = MBB->pred_end(); PI != E; ++PI)
WorkList.push_back(*PI);
} while (!WorkList.empty());
/// current loop.
void MachineLICM::AddToLiveIns(unsigned Reg) {
const std::vector<MachineBasicBlock*> Blocks = CurLoop->getBlocks();
for (unsigned i = 0, e = Blocks.size(); i != e; ++i)
Blocks[i]->addLiveIn(Reg);
}
/// HoistPostRA - When an instruction is found to only use loop invariant
@ -464,11 +440,10 @@ void MachineLICM::HoistPostRA(MachineInstr *MI, unsigned Def) {
MachineBasicBlock *MBB = MI->getParent();
CurPreheader->splice(CurPreheader->getFirstTerminator(), MBB, MI);
// Add register to livein list to BBs in the path from loop header to original
// BB. Note, currently it's not necessary to worry about adding it to all BB's
// with uses. Reload that're reused in successor block(s) are not being
// hoisted.
AddToLiveIns(Def, MBB, CurLoop->getHeader());
// Add register to livein list to all the BBs in the current loop since a
// loop invariant must be kept live throughout the whole loop. This is
// important to ensure later passes do not scavenge the def register.
AddToLiveIns(Def);
++NumPostRAHoisted;
Changed = true;