//
//===----------------------------------------------------------------------===//
//
-// This pass
+// This pass moves instructions into successor blocks, when possible, so that
+// they aren't executed on paths where their results aren't needed.
+//
+// This pass is not intended to be a replacement or a complete alternative
+// for an LLVM-IR-level sinking pass. It is only designed to sink simple
+// constructs that are not exposed before lowering and instruction selection.
//
//===----------------------------------------------------------------------===//
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
-#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
using namespace llvm;
STATISTIC(NumSunk, "Number of machine instructions sunk");
const TargetInstrInfo *TII;
MachineFunction *CurMF; // Current MachineFunction
MachineRegisterInfo *RegInfo; // Machine register information
- MachineDominatorTree *DT; // Machine dominator tree for the current Loop
+ MachineDominatorTree *DT; // Machine dominator tree
public:
static char ID; // Pass identification
- MachineSinking() : MachineFunctionPass((intptr_t)&ID) {}
+ MachineSinking() : MachineFunctionPass(&ID) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
AU.addRequired<MachineDominatorTree>();
AU.addPreserved<MachineDominatorTree>();
bool SinkInstruction(MachineInstr *MI, bool &SawStore);
bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB) const;
};
-
- char MachineSinking::ID = 0;
- RegisterPass<MachineSinking> X("machine-sink", "Machine code sinking");
} // end anonymous namespace
+
+char MachineSinking::ID = 0;
+static RegisterPass<MachineSinking>
+X("machine-sink", "Machine code sinking");
FunctionPass *llvm::createMachineSinkingPass() { return new MachineSinking(); }
bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
- DOUT << "******** Machine Sinking ********\n";
+ DEBUG(errs() << "******** Machine Sinking ********\n");
CurMF = &MF;
TM = &CurMF->getTarget();
}
bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) {
- bool MadeChange = false;
-
// Can't sink anything out of a block that has less than two successors.
- if (MBB.succ_size() <= 1) return false;
-
+ if (MBB.succ_size() <= 1 || MBB.empty()) return false;
+
+ bool MadeChange = false;
+
// Walk the basic block bottom-up. Remember if we saw a store.
- bool SawStore = false;
- for (MachineBasicBlock::iterator I = MBB.end(); I != MBB.begin(); ){
- MachineBasicBlock::iterator LastIt = I;
- if (SinkInstruction(--I, SawStore)) {
- I = LastIt;
- ++NumSunk;
- }
- }
+ MachineBasicBlock::iterator I = MBB.end();
+ --I;
+ bool ProcessedBegin, SawStore = false;
+ do {
+ MachineInstr *MI = I; // The instruction to sink.
+
+ // Predecrement I (if it's not begin) so that it isn't invalidated by
+ // sinking.
+ ProcessedBegin = I == MBB.begin();
+ if (!ProcessedBegin)
+ --I;
+
+ if (SinkInstruction(MI, SawStore))
+ ++NumSunk, MadeChange = true;
+
+ // If we just processed the first instruction in the block, we're done.
+ } while (!ProcessedBegin);
return MadeChange;
}
// also sink them down before their first use in the block. This xform has to
// be careful not to *increase* register pressure though, e.g. sinking
// "x = y + z" down if it kills y and z would increase the live ranges of y
- // and z only the shrink the live range of x.
+ // and z and only shrink the live range of x.
// Loop over all the operands of the specified instruction. If there is
// anything we can't handle, bail out.
} else {
// Virtual register uses are always safe to sink.
if (MO.isUse()) continue;
+
+ // If it's not safe to move defs of the register class, then abort.
+ if (!TII->isSafeToMoveRegClassDefs(RegInfo->getRegClass(Reg)))
+ return false;
// FIXME: This picks a successor to sink into based on having one
// successor that dominates all the uses. However, there are cases where
// If there are no outputs, it must have side-effects.
if (SuccToSinkTo == 0)
return false;
+
+ // It's not safe to sink instructions to EH landing pad. Control flow into
+ // landing pad is implicitly defined.
+ if (SuccToSinkTo->isLandingPad())
+ return false;
+
+ // If is not possible to sink an instruction into its own block. This can
+ // happen with loops.
+ if (MI->getParent() == SuccToSinkTo)
+ return false;
- DEBUG(cerr << "Sink instr " << *MI);
- DEBUG(cerr << "to block " << *SuccToSinkTo);
+ DEBUG(errs() << "Sink instr " << *MI);
+ DEBUG(errs() << "to block " << *SuccToSinkTo);
// 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.
// FIXME: Split critical edges if not backedges.
if (SuccToSinkTo->pred_size() > 1) {
- DEBUG(cerr << " *** PUNTING: Critical edge found\n");
+ DEBUG(errs() << " *** PUNTING: Critical edge found\n");
return false;
}
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