RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-11-23 11:13:28 +01:00
Code Issues Projects Releases Wiki Activity

Simplify the MachineLICM pass by having it only traverse outer

Browse Source 
loops, hoisting instructions all the way out in one step rather
than hoisting them one nest level at a time. Also, make a few
other code simplifications. This speeds up MachineLICM
by several fold.

llvm-svn: 62283
This commit is contained in:
Dan Gohman 2009-01-15 22:01:38 +00:00
parent 46b374f55b
commit 23a5f63b21
2 changed files with 66 additions and 122 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/llvm/CodeGen/MachineBasicBlock.h
View File

@ -263,6 +263,12 @@ public:
MachineInstr *remove(MachineInstr *I) { return Insts.remove(I); }
void clear() { Insts.clear(); }
/// splice - Take an instruction from MBB 'Other' at the position From,
/// and insert it into this MBB right before 'where'.
void splice(iterator where, MachineBasicBlock *Other, iterator From) {
Insts.splice(where, Other->Insts, From);
}
/// splice - Take a block of instructions from MBB 'Other' in the range [From,
/// To), and insert them into this MBB right before 'where'.
void splice(iterator where, MachineBasicBlock *Other, iterator From,

182
lib/CodeGen/MachineLICM.cpp
View File

@ -10,6 +10,14 @@
// This pass performs loop invariant code motion on machine instructions. We
// attempt to remove as much code from the body of a loop as possible.
//
// This pass does not attempt to throttle itself to limit register pressure.
// The register allocation phases are expected to perform rematerialization
// to recover when register pressure is high.
//
// This pass is not intended to be a replacement or a complete alternative
// for the LLVM-IR-level LICM pass. It is only designed to hoist simple
// constructs that are not exposed before lowering and instruction selection.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "machine-licm"
@ -42,6 +50,7 @@ namespace {
// State that is updated as we process loops
bool Changed; // True if a loop is changed.
MachineLoop *CurLoop; // The current loop we are working on.
MachineBasicBlock *CurPreheader; // The preheader for CurLoop.
public:
static char ID; // Pass identification, replacement for typeid
MachineLICM() : MachineFunctionPass(&ID) {}
@ -60,34 +69,6 @@ namespace {
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
/// VisitAllLoops - Visit all of the loops in depth first order and try to
/// hoist invariant instructions from them.
///
void VisitAllLoops(MachineLoop *L) {
const std::vector<MachineLoop*> &SubLoops = L->getSubLoops();
for (MachineLoop::iterator
I = SubLoops.begin(), E = SubLoops.end(); I != E; ++I) {
MachineLoop *ML = *I;
// Traverse the body of the loop in depth first order on the dominator
// tree so that we are guaranteed to see definitions before we see uses.
VisitAllLoops(ML);
HoistRegion(DT->getNode(ML->getHeader()));
}
HoistRegion(DT->getNode(L->getHeader()));
}
/// IsInSubLoop - A little predicate that returns true if the specified
/// basic block is in a subloop of the current one, not the current one
/// itself.
///
bool IsInSubLoop(MachineBasicBlock *BB) {
assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
return LI->getLoopFor(BB) != CurLoop;
}
/// IsLoopInvariantInst - Returns true if the instruction is loop
/// invariant. I.e., all virtual register operands are defined outside of
/// the loop, physical registers aren't accessed (explicitly or implicitly),
@ -95,25 +76,6 @@ namespace {
///
bool IsLoopInvariantInst(MachineInstr &I);
/// FindPredecessors - Get all of the predecessors of the loop that are not
/// back-edges.
///
void FindPredecessors(std::vector<MachineBasicBlock*> &Preds) {
const MachineBasicBlock *Header = CurLoop->getHeader();
for (MachineBasicBlock::const_pred_iterator
I = Header->pred_begin(), E = Header->pred_end(); I != E; ++I)
if (!CurLoop->contains(*I))
Preds.push_back(*I);
}
/// MoveInstToEndOfBlock - Moves the machine instruction to the bottom of
/// the predecessor basic block (but before the terminator instructions).
///
void MoveInstToEndOfBlock(MachineBasicBlock *ToMBB,
MachineBasicBlock *FromMBB,
MachineInstr *MI);
/// HoistRegion - Walk the specified region of the CFG (defined by all
/// blocks dominated by the specified block, and that are in the current
/// loop) in depth first order w.r.t the DominatorTree. This allows us to
@ -135,6 +97,15 @@ X("machinelicm", "Machine Loop Invariant Code Motion");
FunctionPass *llvm::createMachineLICMPass() { return new MachineLICM(); }
/// LoopIsOuterMostWithPreheader - Test if the given loop is the outer-most
/// loop that has a preheader.
static bool LoopIsOuterMostWithPreheader(MachineLoop *CurLoop) {
for (MachineLoop *L = CurLoop->getParentLoop(); L; L = L->getParentLoop())
if (L->getLoopPreheader())
return false;
return true;
}
/// Hoist expressions out of the specified loop. Note, alias info for inner loop
/// is not preserved so it is not a good idea to run LICM multiple times on one
/// loop.
@ -155,10 +126,21 @@ bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
I = LI->begin(), E = LI->end(); I != E; ++I) {
CurLoop = *I;
// Visit all of the instructions of the loop. We want to visit the subloops
// first, though, so that we can hoist their invariants first into their
// containing loop before we process that loop.
VisitAllLoops(CurLoop);
// Only visit outer-most preheader-sporting loops.
if (!LoopIsOuterMostWithPreheader(CurLoop))
continue;
// Determine the block to which to hoist instructions. If we can't find a
// suitable loop preheader, we can't do any hoisting.
//
// FIXME: We are only hoisting if the basic block coming into this loop
// has only one successor. This isn't the case in general because we haven't
// broken critical edges or added preheaders.
CurPreheader = CurLoop->getLoopPreheader();
if (!CurPreheader)
continue;
HoistRegion(DT->getNode(CurLoop->getHeader()));
}
return Changed;
@ -176,18 +158,15 @@ void MachineLICM::HoistRegion(MachineDomTreeNode *N) {
// If this subregion is not in the top level loop at all, exit.
if (!CurLoop->contains(BB)) return;
// Only need to process the contents of this block if it is not part of a
// subloop (which would already have been processed).
if (!IsInSubLoop(BB))
for (MachineBasicBlock::iterator
I = BB->begin(), E = BB->end(); I != E; ) {
MachineInstr &MI = *I++;
for (MachineBasicBlock::iterator
I = BB->begin(), E = BB->end(); I != E; ) {
MachineInstr &MI = *I++;
// Try hoisting the instruction out of the loop. We can only do this if
// all of the operands of the instruction are loop invariant and if it is
// safe to hoist the instruction.
Hoist(MI);
}
// Try hoisting the instruction out of the loop. We can only do this if
// all of the operands of the instruction are loop invariant and if it is
// safe to hoist the instruction.
Hoist(MI);
}
const std::vector<MachineDomTreeNode*> &Children = N->getChildren();
@ -252,20 +231,16 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
if (!MO.isReg())
continue;
if (MO.isDef() && TargetRegisterInfo::isPhysicalRegister(MO.getReg()))
// Don't hoist an instruction that defines a physical register.
unsigned Reg = MO.getReg();
if (Reg == 0) continue;
// Don't hoist an instruction that uses or defines a physical register.
if (TargetRegisterInfo::isPhysicalRegister(Reg))
return false;
if (!MO.isUse())
continue;
unsigned Reg = MO.getReg();
if (Reg == 0) continue;
// Don't hoist instructions that access physical registers.
if (TargetRegisterInfo::isPhysicalRegister(Reg))
return false;
assert(RegInfo->getVRegDef(Reg) &&
"Machine instr not mapped for this vreg?!");
@ -279,64 +254,27 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
return true;
}
/// MoveInstToEndOfBlock - Moves the machine instruction to the bottom of the
/// predecessor basic block (but before the terminator instructions).
///
void MachineLICM::MoveInstToEndOfBlock(MachineBasicBlock *ToMBB,
MachineBasicBlock *FromMBB,
MachineInstr *MI) {
DEBUG({
DOUT << "Hoisting " << *MI;
if (ToMBB->getBasicBlock())
DOUT << " to MachineBasicBlock "
<< ToMBB->getBasicBlock()->getName();
if (FromMBB->getBasicBlock())
DOUT << " from MachineBasicBlock "
<< FromMBB->getBasicBlock()->getName();
DOUT << "\n";
});
MachineBasicBlock::iterator WhereIter = ToMBB->getFirstTerminator();
MachineBasicBlock::iterator To, From = FromMBB->begin();
while (&*From != MI)
++From;
assert(From != FromMBB->end() && "Didn't find instr in BB!");
To = From;
ToMBB->splice(WhereIter, FromMBB, From, ++To);
++NumHoisted;
}
/// Hoist - When an instruction is found to use only loop invariant operands
/// that are safe to hoist, this instruction is called to do the dirty work.
///
void MachineLICM::Hoist(MachineInstr &MI) {
if (!IsLoopInvariantInst(MI)) return;
std::vector<MachineBasicBlock*> Preds;
// Now move the instructions to the predecessor, inserting it before any
// terminator instructions.
DEBUG({
DOUT << "Hoisting " << MI;
if (CurPreheader->getBasicBlock())
DOUT << " to MachineBasicBlock "
<< CurPreheader->getBasicBlock()->getName();
if (MI.getParent()->getBasicBlock())
DOUT << " from MachineBasicBlock "
<< MI.getParent()->getBasicBlock()->getName();
DOUT << "\n";
});
// Non-back-edge predecessors.
FindPredecessors(Preds);
CurPreheader->splice(CurPreheader->getFirstTerminator(), MI.getParent(), &MI);
// Either we don't have any predecessors(?!) or we have more than one, which
// is forbidden.
if (Preds.empty() || Preds.size() != 1) return;
// Check that the predecessor is qualified to take the hoisted instruction.
// I.e., there is only one edge from the predecessor, and it's to the loop
// header.
MachineBasicBlock *MBB = Preds.front();
// FIXME: We are assuming at first that the basic block coming into this loop
// has only one successor. This isn't the case in general because we haven't
// broken critical edges or added preheaders.
if (MBB->succ_size() != 1) return;
assert(*MBB->succ_begin() == CurLoop->getHeader() &&
"The predecessor doesn't feed directly into the loop header!");
// Now move the instructions to the predecessor.
MoveInstToEndOfBlock(MBB, MI.getParent(), &MI);
++NumHoisted;
Changed = true;
}