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Some restructuring in preparation for most aggressive if-conversion.

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llvm-svn: 37231
This commit is contained in:
Evan Cheng 2007-05-18 18:14:37 +00:00
parent d6a33914fb
commit 1ed1741260
1 changed files with 71 additions and 40 deletions
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111
lib/CodeGen/IfConversion.cpp
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@ -39,16 +39,20 @@ namespace {
/// if-conversion feasibility analysis. This includes results from
/// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
/// classification, and common tail block of its successors (if it's a
/// diamond shape).
/// diamond shape), its size, whether it's predicable, and whether any
/// instruction can clobber the 'would-be' predicate.
struct BBInfo {
BBICKind Kind;
unsigned Size;
bool isPredicable;
bool ClobbersPred;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
MachineBasicBlock *FalseBB;
MachineBasicBlock *TailBB;
std::vector<MachineOperand> Cond;
unsigned Size;
BBInfo() : Kind(ICInvalid), BB(0), TrueBB(0), FalseBB(0), TailBB(0), Size(0) {}
BBInfo() : Kind(ICInvalid), Size(0), isPredicable(false),
ClobbersPred(false), BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
};
/// BBAnalysis - Results of if-conversion feasibility analysis indexed by
@ -66,12 +70,12 @@ namespace {
virtual const char *getPassName() const { return "If converter"; }
private:
void AnalyzeBlock(MachineBasicBlock *BB);
void StructuralAnalysis(MachineBasicBlock *BB);
void FeasibilityAnalysis(BBInfo &BBI);
void InitialFunctionAnalysis(MachineFunction &MF,
std::vector<int> &Candidates);
bool IfConvertDiamond(BBInfo &BBI);
bool IfConvertTriangle(BBInfo &BBI);
bool isBlockPredicable(MachineBasicBlock *BB) const;
bool IfConvertDiamond(BBInfo &BBI);
void PredicateBlock(MachineBasicBlock *BB,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm = false);
@ -127,7 +131,10 @@ static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
return NULL;
}
void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
/// StructuralAnalysis - Analyze the structure of the sub-CFG starting from
/// the specified block. Record its successors and whether it looks like an
/// if-conversion candidate.
void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.Kind != ICInvalid)
@ -147,7 +154,7 @@ void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
return;
// Not a candidate if 'true' block is going to be if-converted.
AnalyzeBlock(BBI.TrueBB);
StructuralAnalysis(BBI.TrueBB);
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
if (TrueBBI.Kind != ICNotClassfied)
return;
@ -168,7 +175,7 @@ void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
return;
// Not a candidate if 'false' block is going to be if-converted.
AnalyzeBlock(BBI.FalseBB);
StructuralAnalysis(BBI.FalseBB);
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
if (FalseBBI.Kind != ICNotClassfied)
return;
@ -203,13 +210,36 @@ void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
return;
}
/// FeasibilityAnalysis - Determine if the block is predicable. In most
/// cases, that means all the instructions in the block has M_PREDICABLE flag.
/// Also checks if the block contains any instruction which can clobber a
/// predicate (e.g. condition code register). If so, the block is not
/// 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())
return;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
// TODO: check if instruction clobbers predicate.
if (TII->isTerminatorInstr(I->getOpcode()))
break;
if (!I->isPredicable())
return;
}
BBI.isPredicable = true;
}
/// InitialFunctionAnalysis - Analyze all blocks and find entries for all
/// if-conversion candidates.
void IfConverter::InitialFunctionAnalysis(MachineFunction &MF,
std::vector<int> &Candidates) {
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *BB = I;
AnalyzeBlock(BB);
StructuralAnalysis(BB);
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.Kind == ICTriangleEntry || BBI.Kind == ICDiamondEntry)
Candidates.push_back(BB->getNumber());
@ -245,8 +275,10 @@ static void TransferSuccs(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
/// IfConvertTriangle - If convert a triangle sub-CFG.
///
bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
if (isBlockPredicable(BBI.TrueBB)) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
FeasibilityAnalysis(TrueBBI);
if (TrueBBI.isPredicable) {
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
// Predicate the 'true' block after removing its branch.
@ -276,7 +308,29 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
/// IfConvertDiamond - If convert a diamond sub-CFG.
///
bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
if (isBlockPredicable(BBI.TrueBB) && isBlockPredicable(BBI.FalseBB)) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
FeasibilityAnalysis(TrueBBI);
FeasibilityAnalysis(FalseBBI);
if (TrueBBI.isPredicable && FalseBBI.isPredicable) {
// Check the 'true' and 'false' blocks if either isn't ended with a branch.
// Either the block fallthrough to another block or it ends with a
// return. If it's the former, add a conditional branch to its successor.
bool Proceed = true;
bool TrueNeedCBr = !TrueBBI.TrueBB && BBI.TrueBB->succ_size();
bool FalseNeedCBr = !FalseBBI.TrueBB && BBI.FalseBB->succ_size();
if (TrueNeedCBr && TrueBBI.ClobbersPred) {
TrueBBI.isPredicable = false;
Proceed = false;
}
if (FalseNeedCBr && FalseBBI.ClobbersPred) {
FalseBBI.isPredicable = false;
Proceed = false;
}
if (!Proceed)
return false;
std::vector<MachineInstr*> Dups;
if (!BBI.TailBB) {
// No common merge block. Check if the terminators (e.g. return) are
@ -301,9 +355,6 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
return false; // Can't if-convert. Abort!
}
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
// Remove the duplicated instructions from the 'true' block.
for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
Dups[i]->eraseFromParent();
@ -314,9 +365,8 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
TrueBBI.Size -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(BBI.TrueBB, BBI.Cond);
// Either the 'true' block fallthrough to another block or it ends with a
// return. If it's the former, add a conditional branch to its successor.
if (!TrueBBI.TrueBB && BBI.TrueBB->succ_size())
// Add a conditional branch to 'true' successor if needed.
if (TrueNeedCBr)
TII->InsertBranch(*BBI.TrueBB, *BBI.TrueBB->succ_begin(), NULL, BBI.Cond);
// Predicate the 'false' block.
@ -324,9 +374,8 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
TII->ReverseBranchCondition(NewCond);
PredicateBlock(BBI.FalseBB, NewCond, true);
// Either the 'false' block fallthrough to another block or it ends with a
// return. If it's the former, add a conditional branch to its successor.
if (!FalseBBI.TrueBB && BBI.FalseBB->succ_size())
// Add a conditional branch to 'false' successor if needed.
if (FalseNeedCBr)
TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,NewCond);
// Merge the 'true' and 'false' blocks by copying the instructions
@ -370,24 +419,6 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
return false;
}
/// isBlockPredicable - Returns true if the block is predicable. In most
/// cases, that means all the instructions in the block has M_PREDICABLE flag.
/// It assume all the terminator instructions can be converted or deleted.
bool IfConverter::isBlockPredicable(MachineBasicBlock *BB) const {
const BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.Size == 0 || BBI.Size > TLI->getIfCvtBlockSizeLimit())
return false;
for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
I != E; ++I) {
if (TII->isTerminatorInstr(I->getOpcode()))
continue;
if (!I->isPredicable())
return false;
}
return true;
}
/// 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,