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Preliminary iterative if-conversion support.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37309 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2007-05-23 07:23:16 +00:00
parent 69d555611a
commit a13aa95bc8
1 changed files with 166 additions and 96 deletions
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262
lib/CodeGen/IfConversion.cpp
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@ -28,7 +28,8 @@ STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
namespace {
class IfConverter : public MachineFunctionPass {
enum BBICKind {
ICInvalid, // BB data invalid.
ICNotAnalyzed, // BB has not been analyzed.
ICReAnalyze, // BB must be re-analyzed.
ICNotClassfied, // BB data valid, but not classified.
ICEarlyExit, // BB is entry of an early-exit sub-CFG.
ICTriangle, // BB is entry of a triangle sub-CFG.
@ -43,19 +44,31 @@ namespace {
/// classification, and common tail block of its successors (if it's a
/// diamond shape), its size, whether it's predicable, and whether any
/// instruction can clobber the 'would-be' predicate.
///
/// Kind - Type of block. See BBICKind.
/// NonPredSize - Number of non-predicated instructions.
/// isPredicable - Is it predicable. (FIXME: Remove.)
/// hasEarlyExit - Ends with a return, indirect jump or br to jumptable.
/// ModifyPredicate - FIXME: Not used right now. True if BB would modify
/// the predicate (e.g. has cmp, call, etc.)
/// BB - Corresponding MachineBasicBlock.
/// TrueBB / FalseBB- See AnalyzeBranch().
/// BrCond - Conditions for end of block conditional branches.
/// Predicate - Predicate used in the BB.
struct BBInfo {
BBICKind Kind;
unsigned Size;
unsigned NonPredSize;
bool isPredicable;
bool ClobbersPred;
bool hasEarlyExit;
bool ModifyPredicate;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
MachineBasicBlock *FalseBB;
MachineBasicBlock *TailBB;
std::vector<MachineOperand> Cond;
BBInfo() : Kind(ICInvalid), Size(0), isPredicable(false),
ClobbersPred(false), hasEarlyExit(false),
std::vector<MachineOperand> BrCond;
std::vector<MachineOperand> Predicate;
BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0), isPredicable(false),
hasEarlyExit(false), ModifyPredicate(false),
BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
};
@ -75,13 +88,15 @@ namespace {
private:
void StructuralAnalysis(MachineBasicBlock *BB);
void FeasibilityAnalysis(BBInfo &BBI);
void InitialFunctionAnalysis(MachineFunction &MF,
std::vector<BBInfo*> &Candidates);
void FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond);
void AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates);
void InvalidatePreds(MachineBasicBlock *BB);
bool IfConvertEarlyExit(BBInfo &BBI);
bool IfConvertTriangle(BBInfo &BBI);
bool IfConvertDiamond(BBInfo &BBI);
void PredicateBlock(MachineBasicBlock *BB,
void PredicateBlock(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm = false);
void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI);
@ -101,26 +116,34 @@ bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
BBAnalysis.resize(NumBBs);
std::vector<BBInfo*> Candidates;
// Do an intial analysis for each basic block and finding all the potential
// candidates to perform if-convesion.
InitialFunctionAnalysis(MF, Candidates);
MadeChange = false;
for (unsigned i = 0, e = Candidates.size(); i != e; ++i) {
BBInfo &BBI = *Candidates[i];
switch (BBI.Kind) {
default: assert(false && "Unexpected!");
break;
case ICEarlyExit:
MadeChange |= IfConvertEarlyExit(BBI);
break;
case ICTriangle:
MadeChange |= IfConvertTriangle(BBI);
break;
case ICDiamond:
MadeChange |= IfConvertDiamond(BBI);
break;
while (true) {
bool Change = false;
// Do an intial analysis for each basic block and finding all the potential
// candidates to perform if-convesion.
AnalyzeBlocks(MF, Candidates);
while (!Candidates.empty()) {
BBInfo &BBI = *Candidates.back();
Candidates.pop_back();
switch (BBI.Kind) {
default: assert(false && "Unexpected!");
break;
case ICEarlyExit:
Change |= IfConvertEarlyExit(BBI);
break;
case ICTriangle:
Change |= IfConvertTriangle(BBI);
break;
case ICDiamond:
Change |= IfConvertDiamond(BBI);
break;
}
}
MadeChange |= Change;
if (!Change)
break;
}
BBAnalysis.clear();
@ -145,18 +168,21 @@ static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.Kind != ICInvalid)
return; // Already analyzed.
BBI.BB = BB;
BBI.Size = std::distance(BB->begin(), BB->end());
if (BBI.Kind != ICReAnalyze) {
if (BBI.Kind != ICNotAnalyzed)
return; // Already analyzed.
BBI.BB = BB;
BBI.NonPredSize = std::distance(BB->begin(), BB->end());
// Look for 'root' of a simple (non-nested) triangle or diamond.
BBI.Kind = ICNotClassfied;
bool CanAnalyze = !TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB, BBI.Cond);
// Does it end with a return, indirect jump, or jumptable branch?
BBI.hasEarlyExit = TII->BlockHasNoFallThrough(*BB) && !BBI.TrueBB;
if (!CanAnalyze || !BBI.TrueBB || BBI.Cond.size() == 0)
return;
// Look for 'root' of a simple (non-nested) triangle or diamond.
BBI.Kind = ICNotClassfied;
bool CanAnalyze = !TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB,
BBI.BrCond);
// Does it end with a return, indirect jump, or jumptable branch?
BBI.hasEarlyExit = TII->BlockHasNoFallThrough(*BB) && !BBI.TrueBB;
if (!CanAnalyze || !BBI.TrueBB || BBI.BrCond.size() == 0)
return;
}
// Not a candidate if 'true' block is going to be if-converted.
StructuralAnalysis(BBI.TrueBB);
@ -165,7 +191,7 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
return;
// TODO: Only handle very simple cases for now.
if (TrueBBI.FalseBB || TrueBBI.Cond.size())
if (TrueBBI.FalseBB || TrueBBI.BrCond.size())
return;
// No false branch. This BB must end with a conditional branch and a
@ -181,7 +207,7 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
return;
// TODO: Only handle very simple cases for now.
if (FalseBBI.FalseBB || FalseBBI.Cond.size())
if (FalseBBI.FalseBB || FalseBBI.BrCond.size())
return;
unsigned TrueNumPreds = BBI.TrueBB->pred_size();
@ -228,8 +254,9 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
/// predicable unless it's the last instruction. Note, this function assumes
/// all the terminator instructions can be converted or deleted so it ignore
/// them.
void IfConverter::FeasibilityAnalysis(BBInfo &BBI) {
if (BBI.Size == 0 || BBI.Size > TLI->getIfCvtBlockSizeLimit())
void IfConverter::FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond) {
if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
return;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
@ -241,13 +268,16 @@ void IfConverter::FeasibilityAnalysis(BBInfo &BBI) {
return;
}
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
return;
BBI.isPredicable = true;
}
/// InitialFunctionAnalysis - Analyze all blocks and find entries for all
/// AnalyzeBlocks - Analyze all blocks and find entries for all
/// if-conversion candidates.
void IfConverter::InitialFunctionAnalysis(MachineFunction &MF,
std::vector<BBInfo*> &Candidates) {
void IfConverter::AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates) {
std::set<MachineBasicBlock*> Visited;
MachineBasicBlock *Entry = MF.begin();
for (df_ext_iterator<MachineBasicBlock*> DFI = df_ext_begin(Entry, Visited),
@ -299,42 +329,58 @@ static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
return MachineFunction::iterator(ToBB) == ++Fallthrough;
}
/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
/// to determine if it can be if-converted.
void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI) {
BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
PBBI.Kind = ICReAnalyze;
}
}
/// IfConvertEarlyExit - If convert a early exit sub-CFG.
///
bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
BBI.Kind = ICNotClassfied;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
BBInfo *CvtBBI = &TrueBBI;
BBInfo *NextBBI = &FalseBBI;
bool ReserveCond = false;
if (TrueBBI.Kind != ICChild) {
std::swap(CvtBBI, NextBBI);
ReserveCond = true;
}
FeasibilityAnalysis(*CvtBBI);
if (!CvtBBI->isPredicable) {
BBI.Kind = ICNotClassfied;
return false;
}
std::vector<MachineOperand> NewCond(BBI.Cond);
std::vector<MachineOperand> NewCond(BBI.BrCond);
if (ReserveCond)
TII->ReverseBranchCondition(NewCond);
PredicateBlock(CvtBBI->BB, NewCond);
FeasibilityAnalysis(*CvtBBI, NewCond);
if (!CvtBBI->isPredicable)
return false;
PredicateBlock(*CvtBBI, NewCond);
// Merge converted block into entry block. Also convert the end of the
// block conditional branch (to the non-converted block) into an
// unconditional one.
BBI.Size -= TII->RemoveBranch(*BBI.BB);
BBI.BB->removeSuccessor(CvtBBI->BB);
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
if (!isNextBlock(BBI.BB, NextBBI->BB)) {
std::vector<MachineOperand> NoCond;
TII->InsertBranch(*BBI.BB, NextBBI->BB, NULL, NoCond);
}
std::copy(NewCond.begin(), NewCond.end(), std::back_inserter(BBI.Predicate));
// Update block info.
// Update block info. BB can be iteratively if-converted.
BBI.Kind = ICNotAnalyzed;
BBI.TrueBB = BBI.FalseBB = NULL;
BBI.BrCond.clear();
TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
InvalidatePreds(BBI.BB);
CvtBBI->Kind = ICDead;
// FIXME: Must maintain LiveIns.
@ -345,29 +391,33 @@ bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
/// IfConvertTriangle - If convert a triangle sub-CFG.
///
bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
FeasibilityAnalysis(TrueBBI);
BBI.Kind = ICNotClassfied;
if (!TrueBBI.isPredicable) {
BBI.Kind = ICNotClassfied;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
FeasibilityAnalysis(TrueBBI, BBI.BrCond);
if (!TrueBBI.isPredicable)
return false;
}
// Predicate the 'true' block after removing its branch.
TrueBBI.Size -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(BBI.TrueBB, BBI.Cond);
TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(TrueBBI, BBI.BrCond);
// Join the 'true' and 'false' blocks by copying the instructions
// from the 'false' block to the 'true' block.
BBI.TrueBB->removeSuccessor(BBI.FalseBB);
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
MergeBlocks(TrueBBI, FalseBBI);
// Now merge the entry of the triangle with the true block.
BBI.Size -= TII->RemoveBranch(*BBI.BB);
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, TrueBBI);
std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
std::back_inserter(BBI.Predicate));
// Update block info.
// Update block info. BB can be iteratively if-converted.
BBI.Kind = ICNotClassfied;
BBI.TrueBB = BBI.FalseBB = NULL;
BBI.BrCond.clear();
TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
TrueBBI.Kind = ICDead;
// FIXME: Must maintain LiveIns.
@ -378,12 +428,16 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
/// IfConvertDiamond - If convert a diamond sub-CFG.
///
bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
BBI.Kind = ICNotClassfied;
bool TrueNeedCBr;
bool FalseNeedCBr;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
FeasibilityAnalysis(TrueBBI);
FeasibilityAnalysis(FalseBBI);
FeasibilityAnalysis(TrueBBI, BBI.BrCond);
std::vector<MachineOperand> RevCond(BBI.BrCond);
TII->ReverseBranchCondition(RevCond);
FeasibilityAnalysis(FalseBBI, RevCond);
SmallVector<MachineInstr*, 2> Dups;
bool Proceed = TrueBBI.isPredicable && FalseBBI.isPredicable;
@ -393,11 +447,11 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
// return. If it's the former, add a conditional branch to its successor.
TrueNeedCBr = !TrueBBI.TrueBB && BBI.TrueBB->succ_size();
FalseNeedCBr = !FalseBBI.TrueBB && BBI.FalseBB->succ_size();
if (TrueNeedCBr && TrueBBI.ClobbersPred) {
if (TrueNeedCBr && TrueBBI.ModifyPredicate) {
TrueBBI.isPredicable = false;
Proceed = false;
}
if (FalseNeedCBr && FalseBBI.ClobbersPred) {
if (FalseNeedCBr && FalseBBI.ModifyPredicate) {
FalseBBI.isPredicable = false;
Proceed = false;
}
@ -435,45 +489,42 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
}
}
if (!Proceed) {
BBI.Kind = ICNotClassfied;
if (!Proceed)
return false;
}
// Remove the duplicated instructions from the 'true' block.
for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
Dups[i]->eraseFromParent();
--TrueBBI.Size;
--TrueBBI.NonPredSize;
}
// Predicate the 'true' block after removing its branch.
TrueBBI.Size -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(BBI.TrueBB, BBI.Cond);
TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(TrueBBI, BBI.BrCond);
// Add a conditional branch to 'true' successor if needed.
if (TrueNeedCBr && TrueBBI.ClobbersPred &&
if (TrueNeedCBr && TrueBBI.ModifyPredicate &&
isNextBlock(BBI.TrueBB, *BBI.TrueBB->succ_begin()))
TrueNeedCBr = false;
if (TrueNeedCBr)
TII->InsertBranch(*BBI.TrueBB, *BBI.TrueBB->succ_begin(), NULL, BBI.Cond);
TII->InsertBranch(*BBI.TrueBB, *BBI.TrueBB->succ_begin(), NULL, BBI.BrCond);
// Predicate the 'false' block.
std::vector<MachineOperand> NewCond(BBI.Cond);
TII->ReverseBranchCondition(NewCond);
PredicateBlock(BBI.FalseBB, NewCond, true);
PredicateBlock(FalseBBI, RevCond, true);
// Add a conditional branch to 'false' successor if needed.
if (FalseNeedCBr && !TrueBBI.ClobbersPred &&
if (FalseNeedCBr && !TrueBBI.ModifyPredicate &&
isNextBlock(BBI.FalseBB, *BBI.FalseBB->succ_begin()))
FalseNeedCBr = false;
if (FalseNeedCBr)
TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,NewCond);
TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,
RevCond);
// Merge the 'true' and 'false' blocks by copying the instructions
// from the 'false' block to the 'true' block. That is, unless the true
// block would clobber the predicate, in that case, do the opposite.
BBInfo *CvtBBI;
if (!TrueBBI.ClobbersPred) {
if (!TrueBBI.ModifyPredicate) {
MergeBlocks(TrueBBI, FalseBBI);
CvtBBI = &TrueBBI;
} else {
@ -482,15 +533,16 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
}
// Remove the conditional branch from entry to the blocks.
BBI.Size -= TII->RemoveBranch(*BBI.BB);
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
bool OkToIfcvt = true;
// Merge the combined block into the entry of the diamond if the entry
// block is its only predecessor. Otherwise, insert an unconditional
// branch from entry to the if-converted block.
if (CvtBBI->BB->pred_size() == 1) {
BBI.BB->removeSuccessor(CvtBBI->BB);
MergeBlocks(BBI, *CvtBBI);
CvtBBI = &BBI;
OkToIfcvt = false;
} else {
std::vector<MachineOperand> NoCond;
TII->InsertBranch(*BBI.BB, CvtBBI->BB, NULL, NoCond);
@ -499,14 +551,20 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
// If the if-converted block fallthrough into the tail block, then
// fold the tail block in as well.
if (BBI.TailBB && CvtBBI->BB->succ_size() == 1) {
CvtBBI->Size -= TII->RemoveBranch(*CvtBBI->BB);
CvtBBI->BB->removeSuccessor(BBI.TailBB);
CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
MergeBlocks(*CvtBBI, TailBBI);
TailBBI.Kind = ICDead;
}
// Update block info.
// Update block info. BB may be iteratively if-converted.
if (OkToIfcvt) {
BBI.Kind = ICNotClassfied;
BBI.TrueBB = BBI.FalseBB = NULL;
BBI.BrCond.clear();
TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
InvalidatePreds(BBI.BB);
}
TrueBBI.Kind = ICDead;
FalseBBI.Kind = ICDead;
@ -517,18 +575,23 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
/// PredicateBlock - Predicate every instruction in the block with the specified
/// condition. If IgnoreTerm is true, skip over all terminator instructions.
void IfConverter::PredicateBlock(MachineBasicBlock *BB,
void IfConverter::PredicateBlock(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm) {
for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
MachineInstr *MI = I;
if (IgnoreTerm && TII->isTerminatorInstr(MI->getOpcode()))
continue;
if (!TII->PredicateInstruction(&*I, Cond)) {
if (TII->isPredicated(MI))
continue;
if (!TII->PredicateInstruction(MI, Cond)) {
cerr << "Unable to predication " << *I << "!\n";
abort();
}
}
BBI.NonPredSize = 0;
}
/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
@ -536,8 +599,15 @@ void IfConverter::PredicateBlock(MachineBasicBlock *BB,
void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
ToBBI.BB->splice(ToBBI.BB->end(),
FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
// If FromBBI is previously a successor, remove it from ToBBI's successor
// list and update its TrueBB / FalseBB field if needed.
if (ToBBI.BB->isSuccessor(FromBBI.BB))
ToBBI.BB->removeSuccessor(FromBBI.BB);
// Transfer preds / succs and update size.
TransferPreds(ToBBI.BB, FromBBI.BB);
TransferSuccs(ToBBI.BB, FromBBI.BB);
ToBBI.Size += FromBBI.Size;
FromBBI.Size = 0;
ToBBI.NonPredSize += FromBBI.NonPredSize;
FromBBI.NonPredSize = 0;
}