#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
+#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Statistic.h"
+#include <algorithm>
using namespace llvm;
STATISTIC(NumCPEs, "Number of constpool entries");
/// to a return, unreachable, or unconditional branch).
std::vector<MachineBasicBlock*> WaterList;
+ /// NewWaterList - The subset of WaterList that was created since the
+ /// previous iteration by inserting unconditional branches.
+ SmallSet<MachineBasicBlock*, 4> NewWaterList;
+
typedef std::vector<MachineBasicBlock*>::iterator water_iterator;
/// CPUser - One user of a constant pool, keeping the machine instruction
void AdjustBBOffsetsAfter(MachineBasicBlock *BB, int delta);
bool DecrementOldEntry(unsigned CPI, MachineInstr* CPEMI);
int LookForExistingCPEntry(CPUser& U, unsigned UserOffset);
- bool LookForWater(CPUser&U, unsigned UserOffset,
- MachineBasicBlock *&NewMBB);
- MachineBasicBlock *AcceptWater(water_iterator IP);
+ bool LookForWater(CPUser&U, unsigned UserOffset, water_iterator &WaterIter);
void CreateNewWater(unsigned CPUserIndex, unsigned UserOffset,
MachineBasicBlock *&NewMBB);
bool HandleConstantPoolUser(MachineFunction &MF, unsigned CPUserIndex);
if (CPChange && ++NoCPIters > 30)
llvm_unreachable("Constant Island pass failed to converge!");
DEBUG(dumpBBs());
+
+ // Clear NewWaterList now. If we split a block for branches, it should
+ // appear as "new water" for the next iteration of constant pool placement.
+ NewWaterList.clear();
bool BRChange = false;
for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
/// Split the basic block containing MI into two blocks, which are joined by
-/// an unconditional branch. Update datastructures and renumber blocks to
+/// an unconditional branch. Update data structures and renumber blocks to
/// account for this change and returns the newly created block.
MachineBasicBlock *ARMConstantIslands::SplitBlockBeforeInstr(MachineInstr *MI) {
MachineBasicBlock *OrigBB = MI->getParent();
WaterList.insert(next(IP), NewBB);
else
WaterList.insert(IP, OrigBB);
+ NewWaterList.insert(OrigBB);
// Figure out how large the first NewMBB is. (It cannot
// contain a constpool_entry or tablejump.)
return ((1<<23)-1)*4;
}
-/// AcceptWater - Small amount of common code factored out of the following.
-///
-MachineBasicBlock *ARMConstantIslands::AcceptWater(water_iterator IP) {
- DEBUG(errs() << "found water in range\n");
- MachineBasicBlock *WaterBB = *IP;
- // Remove the original WaterList entry; we want subsequent
- // insertions in this vicinity to go after the one we're
- // about to insert. This considerably reduces the number
- // of times we have to move the same CPE more than once.
- WaterList.erase(IP);
- // CPE goes before following block (NewMBB).
- return next(MachineFunction::iterator(WaterBB));
-}
-
-/// LookForWater - look for an existing entry in the WaterList in which
+/// LookForWater - Look for an existing entry in the WaterList in which
/// we can place the CPE referenced from U so it's within range of U's MI.
-/// Returns true if found, false if not. If it returns true, NewMBB
+/// Returns true if found, false if not. If it returns true, WaterIter
/// is set to the WaterList entry. For Thumb, prefer water that will not
/// introduce padding to water that will. To ensure that this pass
/// terminates, the CPE location for a particular CPUser is only allowed to
/// move to a lower address, so search backward from the end of the list and
/// prefer the first water that is in range.
bool ARMConstantIslands::LookForWater(CPUser &U, unsigned UserOffset,
- MachineBasicBlock *&NewMBB) {
+ water_iterator &WaterIter) {
if (WaterList.empty())
return false;
for (water_iterator IP = prior(WaterList.end()),
B = WaterList.begin();; --IP) {
MachineBasicBlock* WaterBB = *IP;
- // Check if water is in range and at a lower address than the current one.
- if (WaterBB->getNumber() < U.HighWaterMark->getNumber() &&
- WaterIsInRange(UserOffset, WaterBB, U)) {
+ // Check if water is in range and is either at a lower address than the
+ // current "high water mark" or a new water block that was created since
+ // the previous iteration by inserting an unconditional branch. In the
+ // latter case, we want to allow resetting the high water mark back to
+ // this new water since we haven't seen it before. Inserting branches
+ // should be relatively uncommon and when it does happen, we want to be
+ // sure to take advantage of it for all the CPEs near that block, so that
+ // we don't insert more branches than necessary.
+ if (WaterIsInRange(UserOffset, WaterBB, U) &&
+ (WaterBB->getNumber() < U.HighWaterMark->getNumber() ||
+ NewWaterList.count(WaterBB))) {
unsigned WBBId = WaterBB->getNumber();
if (isThumb &&
(BBOffsets[WBBId] + BBSizes[WBBId])%4 != 0) {
IPThatWouldPad = IP;
}
} else {
- NewMBB = AcceptWater(IP);
+ WaterIter = IP;
return true;
}
}
break;
}
if (FoundWaterThatWouldPad) {
- NewMBB = AcceptWater(IPThatWouldPad);
+ WaterIter = IPThatWouldPad;
return true;
}
return false;
MachineInstr *CPEMI = U.CPEMI;
unsigned CPI = CPEMI->getOperand(1).getIndex();
unsigned Size = CPEMI->getOperand(2).getImm();
- MachineBasicBlock *NewMBB;
// Compute this only once, it's expensive. The 4 or 8 is the value the
// hardware keeps in the PC.
unsigned UserOffset = GetOffsetOf(UserMI) + (isThumb ? 4 : 8);
unsigned ID = AFI->createConstPoolEntryUId();
// Look for water where we can place this CPE.
- if (!LookForWater(U, UserOffset, NewMBB)) {
+ MachineBasicBlock *NewIsland = MF.CreateMachineBasicBlock();
+ MachineBasicBlock *NewMBB;
+ water_iterator IP;
+ if (LookForWater(U, UserOffset, IP)) {
+ DEBUG(errs() << "found water in range\n");
+ MachineBasicBlock *WaterBB = *IP;
+
+ // If the original WaterList entry was "new water" on this iteration,
+ // propagate that to the new island. This is just keeping NewWaterList
+ // updated to match the WaterList, which will be updated below.
+ if (NewWaterList.count(WaterBB)) {
+ NewWaterList.erase(WaterBB);
+ NewWaterList.insert(NewIsland);
+ }
+ // The new CPE goes before the following block (NewMBB).
+ NewMBB = next(MachineFunction::iterator(WaterBB));
+
+ } else {
// No water found.
DEBUG(errs() << "No water found\n");
CreateNewWater(CPUserIndex, UserOffset, NewMBB);
+
+ // SplitBlockBeforeInstr adds to WaterList, which is important when it is
+ // called while handling branches so that the water will be seen on the
+ // next iteration for constant pools, but in this context, we don't want
+ // it. Check for this so it will be removed from the WaterList.
+ // Also remove any entry from NewWaterList.
+ MachineBasicBlock *WaterBB = prior(MachineFunction::iterator(NewMBB));
+ IP = std::find(WaterList.begin(), WaterList.end(), WaterBB);
+ if (IP != WaterList.end())
+ NewWaterList.erase(WaterBB);
+
+ // We are adding new water. Update NewWaterList.
+ NewWaterList.insert(NewIsland);
}
+ // Remove the original WaterList entry; we want subsequent insertions in
+ // this vicinity to go after the one we're about to insert. This
+ // considerably reduces the number of times we have to move the same CPE
+ // more than once and is also important to ensure the algorithm terminates.
+ if (IP != WaterList.end())
+ WaterList.erase(IP);
+
// Okay, we know we can put an island before NewMBB now, do it!
- MachineBasicBlock *NewIsland = MF.CreateMachineBasicBlock();
MF.insert(NewMBB, NewIsland);
// Update internal data structures to account for the newly inserted MBB.
projects / oota-llvm.git / commitdiff