#include "llvm/Support/raw_ostream.h"
using namespace llvm;
-static cl::opt<bool>
+static cl::opt<bool>
SplitEdges("machine-sink-split",
cl::desc("Split critical edges during machine sinking"),
cl::init(true), cl::Hidden);
bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB,
MachineBasicBlock *DefMBB,
bool &BreakPHIEdge, bool &LocalUse) const;
- MachineBasicBlock *FindSuccToSinkTo(MachineInstr *MI, bool &BreakPHIEdge);
+ MachineBasicBlock *FindSuccToSinkTo(MachineInstr *MI, MachineBasicBlock *MBB,
+ bool &BreakPHIEdge);
+ bool isProfitableToSinkTo(unsigned Reg, MachineInstr *MI,
+ MachineBasicBlock *MBB,
+ MachineBasicBlock *SuccToSinkTo);
bool PerformTrivialForwardCoalescing(MachineInstr *MI,
MachineBasicBlock *MBB);
} // end anonymous namespace
char MachineSinking::ID = 0;
+char &llvm::MachineSinkingID = MachineSinking::ID;
INITIALIZE_PASS_BEGIN(MachineSinking, "machine-sink",
"Machine code sinking", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_END(MachineSinking, "machine-sink",
"Machine code sinking", false, false)
-FunctionPass *llvm::createMachineSinkingPass() { return new MachineSinking(); }
-
bool MachineSinking::PerformTrivialForwardCoalescing(MachineInstr *MI,
MachineBasicBlock *MBB) {
if (!MI->isCopy())
assert(TargetRegisterInfo::isVirtualRegister(Reg) &&
"Only makes sense for vregs");
+ // Ignore debug uses because debug info doesn't affect the code.
if (MRI->use_nodbg_empty(Reg))
return true;
- // Ignoring debug uses is necessary so debug info doesn't affect the code.
- // This may leave a referencing dbg_value in the original block, before
- // the definition of the vreg. Dwarf generator handles this although the
- // user might not get the right info at runtime.
-
// BreakPHIEdge is true if all the uses are in the successor MBB being sunken
// into and they are all PHI nodes. In this case, machine-sink must break
// the critical edge first. e.g.
return MI->isInsertSubreg() || MI->isSubregToReg() || MI->isRegSequence();
}
-/// collectDebgValues - Scan instructions following MI and collect any
+/// collectDebgValues - Scan instructions following MI and collect any
/// matching DBG_VALUEs.
-static void collectDebugValues(MachineInstr *MI,
+static void collectDebugValues(MachineInstr *MI,
SmallVector<MachineInstr *, 2> & DbgValues) {
DbgValues.clear();
if (!MI->getOperand(0).isReg())
}
}
+/// isPostDominatedBy - Return true if A is post dominated by B.
+static bool isPostDominatedBy(MachineBasicBlock *A, MachineBasicBlock *B) {
+
+ // FIXME - Use real post dominator.
+ if (A->succ_size() != 2)
+ return false;
+ MachineBasicBlock::succ_iterator I = A->succ_begin();
+ if (B == *I)
+ ++I;
+ MachineBasicBlock *OtherSuccBlock = *I;
+ if (OtherSuccBlock->succ_size() != 1 ||
+ *(OtherSuccBlock->succ_begin()) != B)
+ return false;
+
+ return true;
+}
+
+/// isProfitableToSinkTo - Return true if it is profitable to sink MI.
+bool MachineSinking::isProfitableToSinkTo(unsigned Reg, MachineInstr *MI,
+ MachineBasicBlock *MBB,
+ MachineBasicBlock *SuccToSinkTo) {
+ assert (MI && "Invalid MachineInstr!");
+ assert (SuccToSinkTo && "Invalid SinkTo Candidate BB");
+
+ if (MBB == SuccToSinkTo)
+ return false;
+
+ // It is profitable if SuccToSinkTo does not post dominate current block.
+ if (!isPostDominatedBy(MBB, SuccToSinkTo))
+ return true;
+
+ // Check if only use in post dominated block is PHI instruction.
+ bool NonPHIUse = false;
+ for (MachineRegisterInfo::use_nodbg_iterator
+ I = MRI->use_nodbg_begin(Reg), E = MRI->use_nodbg_end();
+ I != E; ++I) {
+ MachineInstr *UseInst = &*I;
+ MachineBasicBlock *UseBlock = UseInst->getParent();
+ if (UseBlock == SuccToSinkTo && !UseInst->isPHI())
+ NonPHIUse = true;
+ }
+ if (!NonPHIUse)
+ return true;
+
+ // If SuccToSinkTo post dominates then also it may be profitable if MI
+ // can further profitably sinked into another block in next round.
+ bool BreakPHIEdge = false;
+ // FIXME - If finding successor is compile time expensive then catch results.
+ if (MachineBasicBlock *MBB2 = FindSuccToSinkTo(MI, SuccToSinkTo, BreakPHIEdge))
+ return isProfitableToSinkTo(Reg, MI, SuccToSinkTo, MBB2);
+
+ // If SuccToSinkTo is final destination and it is a post dominator of current
+ // block then it is not profitable to sink MI into SuccToSinkTo block.
+ return false;
+}
+
/// FindSuccToSinkTo - Find a successor to sink this instruction to.
MachineBasicBlock *MachineSinking::FindSuccToSinkTo(MachineInstr *MI,
- bool &BreakPHIEdge) {
+ MachineBasicBlock *MBB,
+ bool &BreakPHIEdge) {
+
+ assert (MI && "Invalid MachineInstr!");
+ assert (MBB && "Invalid MachineBasicBlock!");
// Loop over all the operands of the specified instruction. If there is
// anything we can't handle, bail out.
- MachineBasicBlock *ParentBlock = MI->getParent();
// SuccToSinkTo - This is the successor to sink this instruction to, once we
// decide.
MachineBasicBlock *SuccToSinkTo = 0;
-
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg()) continue; // Ignore non-register operands.
// If the physreg has no defs anywhere, it's just an ambient register
// and we can freely move its uses. Alternatively, if it's allocatable,
// it could get allocated to something with a def during allocation.
- if (!MRI->def_empty(Reg))
+ if (!MRI->isConstantPhysReg(Reg, *MBB->getParent()))
return NULL;
-
- if (AllocatableSet.test(Reg))
- return NULL;
-
- // Check for a def among the register's aliases too.
- for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
- unsigned AliasReg = *Alias;
- if (!MRI->def_empty(AliasReg))
- return NULL;
-
- if (AllocatableSet.test(AliasReg))
- return NULL;
- }
} else if (!MO.isDead()) {
// A def that isn't dead. We can't move it.
return NULL;
// If a previous operand picked a block to sink to, then this operand
// must be sinkable to the same block.
bool LocalUse = false;
- if (!AllUsesDominatedByBlock(Reg, SuccToSinkTo, ParentBlock,
+ if (!AllUsesDominatedByBlock(Reg, SuccToSinkTo, MBB,
BreakPHIEdge, LocalUse))
return NULL;
// Otherwise, we should look at all the successors and decide which one
// we should sink to.
- for (MachineBasicBlock::succ_iterator SI = ParentBlock->succ_begin(),
- E = ParentBlock->succ_end(); SI != E; ++SI) {
- MachineBasicBlock *SuccBlock = *SI;
+ for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
+ E = MBB->succ_end(); SI != E; ++SI) {
+ MachineBasicBlock *SuccBlock = *SI;
bool LocalUse = false;
- if (AllUsesDominatedByBlock(Reg, SuccBlock, ParentBlock,
+ if (AllUsesDominatedByBlock(Reg, SuccBlock, MBB,
BreakPHIEdge, LocalUse)) {
SuccToSinkTo = SuccBlock;
break;
// If we couldn't find a block to sink to, ignore this instruction.
if (SuccToSinkTo == 0)
return NULL;
+ else if (!isProfitableToSinkTo(Reg, MI, MBB, SuccToSinkTo))
+ return NULL;
}
}
// It is not possible to sink an instruction into its own block. This can
// happen with loops.
- if (ParentBlock == SuccToSinkTo)
+ if (MBB == SuccToSinkTo)
return NULL;
// It's not safe to sink instructions to EH landing pad. Control flow into
// and z and only shrink the live range of x.
bool BreakPHIEdge = false;
- MachineBasicBlock *SuccToSinkTo = FindSuccToSinkTo(MI, BreakPHIEdge);
+ MachineBasicBlock *ParentBlock = MI->getParent();
+ MachineBasicBlock *SuccToSinkTo = FindSuccToSinkTo(MI, ParentBlock, BreakPHIEdge);
// If there are no outputs, it must have side-effects.
if (SuccToSinkTo == 0)
DEBUG(dbgs() << "Sink instr " << *MI << "\tinto block " << *SuccToSinkTo);
- MachineBasicBlock *ParentBlock = MI->getParent();
-
// If the block has multiple predecessors, this would introduce computation on
// a path that it doesn't already exist. We could split the critical edge,
// but for now we just punt.