mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-17 21:29:20 +00:00
Make tail merging handle many more cases (all it can, I think).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36966 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
parent
0f1621bb4c
commit
76b38fcabe
@ -336,7 +336,16 @@ static bool ShouldSplitFirstBlock(MachineBasicBlock *MBB1,
|
|||||||
MachineBasicBlock::iterator MBB1I,
|
MachineBasicBlock::iterator MBB1I,
|
||||||
MachineBasicBlock *MBB2,
|
MachineBasicBlock *MBB2,
|
||||||
MachineBasicBlock::iterator MBB2I,
|
MachineBasicBlock::iterator MBB2I,
|
||||||
const TargetInstrInfo *TII) {
|
const TargetInstrInfo *TII,
|
||||||
|
MachineBasicBlock *PredBB) {
|
||||||
|
// If one block falls through into the common successor, choose that
|
||||||
|
// one to split; it is one instruction less to do that.
|
||||||
|
if (PredBB) {
|
||||||
|
if (MBB1 == PredBB)
|
||||||
|
return true;
|
||||||
|
else if (MBB2 == PredBB)
|
||||||
|
return false;
|
||||||
|
}
|
||||||
// TODO: if we had some notion of which block was hotter, we could split
|
// TODO: if we had some notion of which block was hotter, we could split
|
||||||
// the hot block, so it is the fall-through. Since we don't have profile info
|
// the hot block, so it is the fall-through. Since we don't have profile info
|
||||||
// make a decision based on which will hurt most to split.
|
// make a decision based on which will hurt most to split.
|
||||||
@ -349,6 +358,31 @@ static bool ShouldSplitFirstBlock(MachineBasicBlock *MBB1,
|
|||||||
return MBB1Time < MBB2Time;
|
return MBB1Time < MBB2Time;
|
||||||
}
|
}
|
||||||
|
|
||||||
|
// CurMBB needs to add an unconditional branch to SuccMBB (we removed these
|
||||||
|
// branches temporarily for tail merging). In the case where CurMBB ends
|
||||||
|
// with a conditional branch to the next block, optimize by reversing the
|
||||||
|
// test and conditionally branching to SuccMBB instead.
|
||||||
|
|
||||||
|
static void FixTail(MachineBasicBlock* CurMBB, MachineBasicBlock *SuccBB,
|
||||||
|
const TargetInstrInfo *TII) {
|
||||||
|
MachineFunction *MF = CurMBB->getParent();
|
||||||
|
MachineFunction::iterator I = next(MachineFunction::iterator(CurMBB));
|
||||||
|
MachineBasicBlock *TBB = 0, *FBB = 0;
|
||||||
|
std::vector<MachineOperand> Cond;
|
||||||
|
if (I != MF->end() &&
|
||||||
|
!TII->AnalyzeBranch(*CurMBB, TBB, FBB, Cond)) {
|
||||||
|
MachineBasicBlock *NextBB = I;
|
||||||
|
if (TBB == NextBB && Cond.size() && !FBB) {
|
||||||
|
if (!TII->ReverseBranchCondition(Cond)) {
|
||||||
|
TII->RemoveBranch(*CurMBB);
|
||||||
|
TII->InsertBranch(*CurMBB, SuccBB, NULL, Cond);
|
||||||
|
return;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
TII->InsertBranch(*CurMBB, SuccBB, NULL, std::vector<MachineOperand>());
|
||||||
|
}
|
||||||
|
|
||||||
// See if any of the blocks in MergePotentials (which all have a common single
|
// See if any of the blocks in MergePotentials (which all have a common single
|
||||||
// successor, or all have no successor) can be tail-merged. If there is a
|
// successor, or all have no successor) can be tail-merged. If there is a
|
||||||
// successor, any blocks in MergePotentials that are not tail-merged and
|
// successor, any blocks in MergePotentials that are not tail-merged and
|
||||||
@ -375,7 +409,7 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
|
|||||||
// give up.
|
// give up.
|
||||||
if (CurHash != PrevHash) {
|
if (CurHash != PrevHash) {
|
||||||
if (SuccBB && CurMBB != PredBB)
|
if (SuccBB && CurMBB != PredBB)
|
||||||
TII->InsertBranch(*CurMBB, SuccBB, NULL, std::vector<MachineOperand>());
|
FixTail(CurMBB, SuccBB, TII);
|
||||||
MergePotentials.pop_back();
|
MergePotentials.pop_back();
|
||||||
continue;
|
continue;
|
||||||
}
|
}
|
||||||
@ -390,6 +424,8 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
|
|||||||
|
|
||||||
// If the tails don't have at least two instructions in common, see if there
|
// If the tails don't have at least two instructions in common, see if there
|
||||||
// is anything else in the equivalence class that does match.
|
// is anything else in the equivalence class that does match.
|
||||||
|
// Since instructions may get combined later (e.g. single stores into
|
||||||
|
// store multiple) this measure is not particularly accurate.
|
||||||
if (CommonTailLen < 2) {
|
if (CommonTailLen < 2) {
|
||||||
unsigned FoundMatch = ~0U;
|
unsigned FoundMatch = ~0U;
|
||||||
for (int i = MergePotentials.size()-2;
|
for (int i = MergePotentials.size()-2;
|
||||||
@ -408,7 +444,7 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
|
|||||||
if (FoundMatch == ~0U) {
|
if (FoundMatch == ~0U) {
|
||||||
// Put the unconditional branch back, if we need one.
|
// Put the unconditional branch back, if we need one.
|
||||||
if (SuccBB && CurMBB != PredBB)
|
if (SuccBB && CurMBB != PredBB)
|
||||||
TII->InsertBranch(*CurMBB, SuccBB, NULL, std::vector<MachineOperand>());
|
FixTail(CurMBB, SuccBB, TII);
|
||||||
MergePotentials.pop_back();
|
MergePotentials.pop_back();
|
||||||
continue;
|
continue;
|
||||||
}
|
}
|
||||||
@ -428,7 +464,7 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
|
|||||||
}
|
}
|
||||||
|
|
||||||
// Decide whether we want to split CurMBB or MBB2.
|
// Decide whether we want to split CurMBB or MBB2.
|
||||||
if (ShouldSplitFirstBlock(CurMBB, BBI1, MBB2, BBI2, TII)) {
|
if (ShouldSplitFirstBlock(CurMBB, BBI1, MBB2, BBI2, TII, PredBB)) {
|
||||||
CurMBB = SplitMBBAt(*CurMBB, BBI1);
|
CurMBB = SplitMBBAt(*CurMBB, BBI1);
|
||||||
BBI1 = CurMBB->begin();
|
BBI1 = CurMBB->begin();
|
||||||
MergePotentials.back().second = CurMBB;
|
MergePotentials.back().second = CurMBB;
|
||||||
@ -457,49 +493,69 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
|
|||||||
}
|
}
|
||||||
|
|
||||||
bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
|
bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
|
||||||
MadeChange = false;
|
|
||||||
|
|
||||||
if (!EnableTailMerge) return false;
|
if (!EnableTailMerge) return false;
|
||||||
|
|
||||||
|
MadeChange = false;
|
||||||
|
|
||||||
// First find blocks with no successors.
|
// First find blocks with no successors.
|
||||||
|
MergePotentials.clear();
|
||||||
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
|
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
|
||||||
if (I->succ_empty())
|
if (I->succ_empty())
|
||||||
MergePotentials.push_back(std::make_pair(HashEndOfMBB(I), I));
|
MergePotentials.push_back(std::make_pair(HashEndOfMBB(I), I));
|
||||||
}
|
}
|
||||||
// See if we can do any crossjumping on those.
|
// See if we can do any tail merging on those.
|
||||||
MadeChange |= TryMergeBlocks(NULL, NULL);
|
MadeChange |= TryMergeBlocks(NULL, NULL);
|
||||||
|
|
||||||
MergePotentials.clear();
|
// Look at blocks (IBB) with multiple predecessors (PBB).
|
||||||
// Look at blocks with two predecessors, where each predecessor has either:
|
// We change each predecessor to a canonical form, by
|
||||||
// - a single successor, or
|
// (1) temporarily removing any unconditional branch from the predecessor
|
||||||
// - two successors, where successor I is reached either by ubr or fallthrough.
|
// to IBB, and
|
||||||
// The two-successor case where successor I is reached by cbr
|
// (2) alter conditional branches so they branch to the other block
|
||||||
// from both blocks is handled by the preceding case (when we consider the
|
// not IBB; this may require adding back an unconditional branch to IBB
|
||||||
// other, fallthough block).
|
// later, where there wasn't one coming in. E.g.
|
||||||
// FIXME: The two-successor case where I is reached by cbr
|
// Bcc IBB
|
||||||
// from one block, and by fallthrough/ubr from the other, is not handled yet.
|
// fallthrough to QBB
|
||||||
// Beware that sometimes blocks are in the predecessor list, but can't really
|
// here becomes
|
||||||
// jump to the "successor" we're looking at. Tolerate this.
|
// Bncc QBB
|
||||||
|
// with a conceptual B to IBB after that, which never actually exists.
|
||||||
|
// With those changes, we see whether the predecessors' tails match,
|
||||||
|
// and merge them if so. We change things out of canonical form and
|
||||||
|
// back to the way they were later in the process. (OptimizeBranches
|
||||||
|
// would undo some of this, but we can't use it, because we'd get into
|
||||||
|
// a compile-time infinite loop repeatedly doing and undoing the same
|
||||||
|
// transformations.)
|
||||||
|
|
||||||
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
|
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
|
||||||
if (!I->succ_empty() && I->pred_size() >= 2) {
|
if (!I->succ_empty() && I->pred_size() >= 2) {
|
||||||
MachineBasicBlock *IBB = I;
|
MachineBasicBlock *IBB = I;
|
||||||
MachineBasicBlock *PredBB = prior(I);
|
MachineBasicBlock *PredBB = prior(I);
|
||||||
|
MergePotentials.clear();
|
||||||
for (MachineBasicBlock::pred_iterator P = I->pred_begin(), E2 = I->pred_end();
|
for (MachineBasicBlock::pred_iterator P = I->pred_begin(), E2 = I->pred_end();
|
||||||
P != E2; ++P) {
|
P != E2; ++P) {
|
||||||
MachineBasicBlock* PBB = *P;
|
MachineBasicBlock* PBB = *P;
|
||||||
|
// Skip blocks that loop to themselves, can't tail merge these.
|
||||||
|
if (PBB==IBB)
|
||||||
|
continue;
|
||||||
MachineBasicBlock *TBB = 0, *FBB = 0;
|
MachineBasicBlock *TBB = 0, *FBB = 0;
|
||||||
std::vector<MachineOperand> Cond;
|
std::vector<MachineOperand> Cond;
|
||||||
|
if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond)) {
|
||||||
|
// Failing case: IBB is the target of a cbr, and
|
||||||
|
// we cannot reverse the branch.
|
||||||
|
std::vector<MachineOperand> NewCond(Cond);
|
||||||
|
if (Cond.size() && TBB==IBB) {
|
||||||
|
if (TII->ReverseBranchCondition(NewCond))
|
||||||
|
continue;
|
||||||
|
// This is the QBB case described above
|
||||||
|
if (!FBB)
|
||||||
|
FBB = next(MachineFunction::iterator(PBB));
|
||||||
|
}
|
||||||
// Remove the unconditional branch at the end, if any.
|
// Remove the unconditional branch at the end, if any.
|
||||||
if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond) &&
|
if (TBB && (Cond.size()==0 || FBB)) {
|
||||||
((!FBB && Cond.size()==0) || // single successor
|
|
||||||
(!FBB && TBB!=IBB) || // cbr elsewhere, fallthrough to I
|
|
||||||
(FBB && FBB==IBB))) { // cbr then branch to I
|
|
||||||
if (TBB) {
|
|
||||||
TII->RemoveBranch(*PBB);
|
TII->RemoveBranch(*PBB);
|
||||||
if (TBB!=IBB)
|
if (Cond.size())
|
||||||
// reinsert conditional branch only, for now
|
// reinsert conditional branch only, for now
|
||||||
TII->InsertBranch(*PBB, TBB, 0, Cond);
|
TII->InsertBranch(*PBB, (TBB==IBB) ? FBB : TBB, 0, NewCond);
|
||||||
}
|
}
|
||||||
MergePotentials.push_back(std::make_pair(HashEndOfMBB(PBB), *P));
|
MergePotentials.push_back(std::make_pair(HashEndOfMBB(PBB), *P));
|
||||||
}
|
}
|
||||||
@ -511,12 +567,9 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
|
|||||||
// of removing blocks in TryMergeBlocks.
|
// of removing blocks in TryMergeBlocks.
|
||||||
if (MergePotentials.size()==1 &&
|
if (MergePotentials.size()==1 &&
|
||||||
(MergePotentials.begin())->second != PredBB)
|
(MergePotentials.begin())->second != PredBB)
|
||||||
TII->InsertBranch(*((MergePotentials.begin())->second), I, NULL,
|
FixTail((MergePotentials.begin())->second, I, TII);
|
||||||
std::vector<MachineOperand>());
|
|
||||||
MergePotentials.clear();
|
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
return MadeChange;
|
return MadeChange;
|
||||||
}
|
}
|
||||||
|
|
||||||
@ -962,12 +1015,18 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
|
|||||||
MachineBasicBlock *PredBB = *PI;
|
MachineBasicBlock *PredBB = *PI;
|
||||||
MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough;
|
MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough;
|
||||||
if (PredBB != MBB && !CanFallThrough(PredBB)
|
if (PredBB != MBB && !CanFallThrough(PredBB)
|
||||||
|
&& (!CurFallsThru || !CurTBB || !CurFBB)
|
||||||
&& (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
|
&& (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
|
||||||
// If the current block doesn't fall through, just move it.
|
// If the current block doesn't fall through, just move it.
|
||||||
// If the current block can fall through and does not end with a
|
// If the current block can fall through and does not end with a
|
||||||
// conditional branch, we need to append an unconditional jump to
|
// conditional branch, we need to append an unconditional jump to
|
||||||
// the (current) next block. To avoid a possible compile-time
|
// the (current) next block. To avoid a possible compile-time
|
||||||
// infinite loop, move blocks only backward in this case.
|
// infinite loop, move blocks only backward in this case.
|
||||||
|
// Also, if there are already 2 branches here, we cannot add a third;
|
||||||
|
// this means we have the case
|
||||||
|
// Bcc next
|
||||||
|
// B elsewhere
|
||||||
|
// next:
|
||||||
if (CurFallsThru) {
|
if (CurFallsThru) {
|
||||||
MachineBasicBlock *NextBB = next(MachineFunction::iterator(MBB));
|
MachineBasicBlock *NextBB = next(MachineFunction::iterator(MBB));
|
||||||
CurCond.clear();
|
CurCond.clear();
|
||||||
|
Loading…
Reference in New Issue
Block a user