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Restructure code to reduce ifcvt compile time cost. 

llvm-svn: 37543
This commit is contained in:
Evan Cheng 2007-06-11 22:26:22 +00:00
parent 536ac4dca7
commit 4dd31a7b1b
1 changed files with 196 additions and 158 deletions
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354
llvm/lib/CodeGen/IfConversion.cpp
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@ -55,17 +55,13 @@ STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
namespace {
class IfConverter : public MachineFunctionPass {
enum BBICKind {
ICNotAnalyzed, // BB has not been analyzed.
ICReAnalyze, // BB must be re-analyzed.
ICNotClassfied, // BB data valid, but not classified.
ICSimple, // BB is entry of an one split, no rejoin sub-CFG.
ICSimpleFalse, // Same as ICSimple, but on the false path.
ICTriangle, // BB is entry of a triangle sub-CFG.
ICTriangleFalse, // Same as ICTriangle, but on the false path.
ICTriangleFRev, // Same as ICTriangleFalse, but false path rev condition.
ICDiamond, // BB is entry of a diamond sub-CFG.
ICChild, // BB is part of the sub-CFG that'll be predicated.
ICDead // BB cannot be if-converted again.
ICDiamond // BB is entry of a diamond sub-CFG.
};
/// BBInfo - One per MachineBasicBlock, this is used to cache the result
@ -76,29 +72,41 @@ namespace {
/// instruction can clobber the 'would-be' predicate.
///
/// Kind - Type of block. See BBICKind.
/// NonPredSize - Number of non-predicated instructions.
/// IsAnalyzable - True if AnalyzeBranch() returns false.
/// ModifyPredicate - True if BB would modify the predicate (e.g. has
/// IsDone - True if BB is not to be considered for ifcvt.
/// IsBeingAnalyzed - True if BB is currently being analyzed.
/// IsAnalyzed - True if BB has been analyzed (info is still valid).
/// IsEnqueued - True if BB has been enqueued to be ifcvt'ed.
/// IsBrAnalyzable - True if AnalyzeBranch() returns false.
/// HasFallThrough - True if BB may fallthrough to the following BB.
/// IsUnpredicable - True if BB is known to be unpredicable.
/// ClobbersPredicate- True if BB would modify the predicate (e.g. has
/// cmp, call, etc.)
/// NonPredSize - Number of non-predicated instructions.
/// 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;
bool IsDone : 1;
bool IsBeingAnalyzed : 1;
bool IsAnalyzed : 1;
bool IsEnqueued : 1;
bool IsBrAnalyzable : 1;
bool HasFallThrough : 1;
bool IsUnpredicable : 1;
bool ClobbersPred : 1;
unsigned NonPredSize;
bool IsAnalyzable;
bool HasFallThrough;
bool ModifyPredicate;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
MachineBasicBlock *FalseBB;
MachineBasicBlock *TailBB;
std::vector<MachineOperand> BrCond;
std::vector<MachineOperand> Predicate;
BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0),
IsAnalyzable(false), HasFallThrough(false),
ModifyPredicate(false),
BBInfo() : Kind(ICNotClassfied), IsDone(false), IsBeingAnalyzed(false),
IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
HasFallThrough(false), IsUnpredicable(false),
ClobbersPred(false), NonPredSize(0),
BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
};
@ -127,7 +135,7 @@ namespace {
bool FalseBranch = false) const;
bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const;
void ScanInstructions(BBInfo &BBI);
void AnalyzeBlock(MachineBasicBlock *BB);
BBInfo &AnalyzeBlock(MachineBasicBlock *BB);
bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond,
bool isTriangle = false, bool RevBranch = false);
bool AttemptRestructuring(BBInfo &BBI);
@ -145,7 +153,7 @@ namespace {
// blockAlwaysFallThrough - Block ends without a terminator.
bool blockAlwaysFallThrough(BBInfo &BBI) const {
return BBI.IsAnalyzable && BBI.TrueBB == NULL;
return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
}
// IfcvtCandidateCmp - Used to sort if-conversion candidates.
@ -192,15 +200,15 @@ bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
BBInfo &BBI = *Candidates.back();
Candidates.pop_back();
// If the block has been evicted out of the queue or it has already been
// marked dead (due to it being predicated), then skip it.
if (!BBI.IsEnqueued || BBI.IsDone)
continue;
bool RetVal = false;
switch (BBI.Kind) {
default: assert(false && "Unexpected!");
break;
case ICReAnalyze:
// One or more of 'children' have been modified, abort!
case ICDead:
// Block has been already been if-converted, abort!
break;
case ICSimple:
case ICSimpleFalse: {
bool isFalse = BBI.Kind == ICSimpleFalse;
@ -304,6 +312,9 @@ static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
/// ValidSimple - Returns true if the 'true' block (along with its
/// predecessor) forms a valid simple shape for ifcvt.
bool IfConverter::ValidSimple(BBInfo &TrueBBI) const {
if (TrueBBI.IsBeingAnalyzed)
return false;
return !blockAlwaysFallThrough(TrueBBI) &&
TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1;
}
@ -312,6 +323,9 @@ bool IfConverter::ValidSimple(BBInfo &TrueBBI) const {
/// with their common predecessor) forms a valid triangle shape for ifcvt.
bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch) const {
if (TrueBBI.IsBeingAnalyzed)
return false;
if (TrueBBI.BB->pred_size() != 1)
return false;
@ -328,6 +342,9 @@ bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid diamond shape for ifcvt.
bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const {
if (TrueBBI.IsBeingAnalyzed || FalseBBI.IsBeingAnalyzed)
return false;
MachineBasicBlock *TT = TrueBBI.TrueBB;
MachineBasicBlock *FT = FalseBBI.TrueBB;
@ -337,7 +354,7 @@ bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const {
FT = getNextBlock(FalseBBI.BB);
if (TT != FT)
return false;
if (TT == NULL && (TrueBBI.IsAnalyzable || FalseBBI.IsAnalyzable))
if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
return false;
// FIXME: Allow false block to have an early exit?
return (TrueBBI.BB->pred_size() == 1 &&
@ -345,59 +362,155 @@ bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const {
!TrueBBI.FalseBB && !FalseBBI.FalseBB);
}
/// ScanInstructions - Scan all the instructions in the block to 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.
void IfConverter::ScanInstructions(BBInfo &BBI) {
if (BBI.IsDone)
return;
// First analyze the end of BB branches.
BBI.TrueBB = BBI.FalseBB;
BBI.BrCond.clear();
BBI.IsBrAnalyzable =
!TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
if (BBI.BrCond.size()) {
// No false branch. This BB must end with a conditional branch and a
// fallthrough.
if (!BBI.FalseBB)
BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
assert(BBI.FalseBB && "Expected to find the fallthrough block!");
}
// Then scan all the instructions.
BBI.NonPredSize = 0;
BBI.ClobbersPred = false;
bool SeenCondBr = false;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
const TargetInstrDescriptor *TID = I->getInstrDescriptor();
bool isPredicated = TII->isPredicated(I);
bool isCondBr = BBI.IsBrAnalyzable &&
(TID->Flags & M_BRANCH_FLAG) != 0 && (TID->Flags & M_BARRIER_FLAG) == 0;
if (!isPredicated && !isCondBr)
BBI.NonPredSize++;
if (BBI.ClobbersPred && !isPredicated) {
// Predicate modification instruction should end the block (except for
// already predicated instructions and end of block branches).
if (isCondBr) {
SeenCondBr = true;
// Conditional branches is not predicable. But it may be eliminated.
continue;
}
// Predicate may have been modified, the subsequent (currently)
// unpredocated instructions cannot be correctly predicated.
BBI.IsUnpredicable = true;
return;
}
if (TID->Flags & M_CLOBBERS_PRED)
BBI.ClobbersPred = true;
if (!I->isPredicable()) {
BBI.IsUnpredicable = true;
return;
}
}
}
/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
/// predicated by the specified predicate.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Pred,
bool isTriangle, bool RevBranch) {
// Forget about it if it's unpredicable.
if (BBI.IsUnpredicable)
return false;
// If the block is dead, or it is going to be the entry block of a sub-CFG
// that will be if-converted, then it cannot be predicated.
if (BBI.IsDone || BBI.IsEnqueued)
return false;
// Check predication threshold.
if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
return false;
// If it is already predicated, check if its predicate subsumes the new
// predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
return false;
if (BBI.BrCond.size()) {
if (!isTriangle)
return false;
// Test predicate subsumsion.
std::vector<MachineOperand> RevPred(Pred);
std::vector<MachineOperand> Cond(BBI.BrCond);
if (RevBranch) {
if (TII->ReverseBranchCondition(Cond))
return false;
}
if (TII->ReverseBranchCondition(RevPred) ||
!TII->SubsumesPredicate(Cond, RevPred))
return false;
}
return true;
}
/// AnalyzeBlock - 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::AnalyzeBlock(MachineBasicBlock *BB) {
IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.Kind == ICReAnalyze) {
BBI.BrCond.clear();
BBI.TrueBB = BBI.FalseBB = NULL;
} else {
if (BBI.Kind != ICNotAnalyzed)
return; // Already analyzed.
BBI.BB = BB;
BBI.NonPredSize = std::distance(BB->begin(), BB->end());
}
if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
return BBI;
// Look for 'root' of a simple (non-nested) triangle or diamond.
BBI.BB = BB;
BBI.IsBeingAnalyzed = true;
BBI.Kind = ICNotClassfied;
BBI.IsAnalyzable =
!TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
BBI.HasFallThrough = BBI.IsAnalyzable && BBI.FalseBB == NULL;
ScanInstructions(BBI);
// Unanalyable or ends with fallthrough or unconditional branch.
if (!BBI.IsAnalyzable || BBI.BrCond.size() == 0)
return;
// Do not ifcvt if either path is a back edge to the entry block.
if (BBI.TrueBB == BB || BBI.FalseBB == BB)
return;
AnalyzeBlock(BBI.TrueBB);
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
// No false branch. This BB must end with a conditional branch and a
// fallthrough.
if (!BBI.FalseBB)
BBI.FalseBB = findFalseBlock(BB, BBI.TrueBB);
assert(BBI.FalseBB && "Expected to find the fallthrough block!");
AnalyzeBlock(BBI.FalseBB);
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
// If both paths are dead, then forget about it.
if (TrueBBI.Kind == ICDead && FalseBBI.Kind == ICDead) {
BBI.Kind = ICDead;
return;
if (!BBI.IsBrAnalyzable || BBI.BrCond.size() == 0) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
// Do not ifcvt if either path is a back edge to the entry block.
if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
BBInfo &TrueBBI = AnalyzeBlock(BBI.TrueBB);
BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB);
if (TrueBBI.IsDone && FalseBBI.IsDone) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
// Look for more opportunities to if-convert a triangle. Try to restructure
// the CFG to form a triangle with the 'false' path.
std::vector<MachineOperand> RevCond(BBI.BrCond);
bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) &&
!(TrueBBI.ModifyPredicate && FalseBBI.ModifyPredicate) &&
!(TrueBBI.ClobbersPred && FalseBBI.ClobbersPred) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
@ -409,7 +522,6 @@ void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
// TailBB
// Note TailBB can be empty.
BBI.Kind = ICDiamond;
TrueBBI.Kind = FalseBBI.Kind = ICChild;
BBI.TailBB = TrueBBI.TrueBB;
} else {
// FIXME: Consider duplicating if BB is small.
@ -423,7 +535,6 @@ void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
// | /
// FBB
BBI.Kind = ICTriangle;
TrueBBI.Kind = ICChild;
} else if (ValidSimple(TrueBBI) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
// Simple (split, no rejoin):
@ -434,93 +545,24 @@ void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
// |
// FBB
BBI.Kind = ICSimple;
TrueBBI.Kind = ICChild;
} else if (CanRevCond) {
// Try the other path...
if (ValidTriangle(FalseBBI, TrueBBI) &&
FeasibilityAnalysis(FalseBBI, RevCond, true)) {
BBI.Kind = ICTriangleFalse;
FalseBBI.Kind = ICChild;
} else if (ValidTriangle(FalseBBI, TrueBBI, true) &&
FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
BBI.Kind = ICTriangleFRev;
FalseBBI.Kind = ICChild;
} else if (ValidSimple(FalseBBI) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
BBI.Kind = ICSimpleFalse;
FalseBBI.Kind = ICChild;
}
}
}
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.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Pred,
bool isTriangle, bool RevBranch) {
// If the block is dead, or it is going to be the entry block of a sub-CFG
// that will be if-converted, then it cannot be predicated.
if (BBI.Kind != ICNotAnalyzed &&
BBI.Kind != ICNotClassfied &&
BBI.Kind != ICChild)
return false;
// Check predication threshold.
if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
return false;
// If it is already predicated, check if its predicate subsumes the new
// predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
return false;
bool SeenPredMod = false;
bool SeenCondBr = false;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
const TargetInstrDescriptor *TID = I->getInstrDescriptor();
if (SeenPredMod) {
// Predicate modification instruction should end the block (except for
// already predicated instructions and end of block branches).
if (!TII->isPredicated(I)) {
// This is the 'true' block of a triangle, i.e. its 'true' block is
// the same as the 'false' block of the entry. So false positive
// is ok.
if (isTriangle && !SeenCondBr && BBI.IsAnalyzable &&
(TID->Flags & M_BRANCH_FLAG) != 0 &&
(TID->Flags & M_BARRIER_FLAG) == 0) {
// This is the first conditional branch, test predicate subsumsion.
std::vector<MachineOperand> RevPred(Pred);
std::vector<MachineOperand> Cond(BBI.BrCond);
if (RevBranch) {
if (TII->ReverseBranchCondition(Cond))
return false;
}
if (TII->ReverseBranchCondition(RevPred) ||
!TII->SubsumesPredicate(Cond, RevPred))
return false;
SeenCondBr = true;
continue; // Conditional branches is not predicable.
}
return false;
}
}
if (TID->Flags & M_CLOBBERS_PRED) {
BBI.ModifyPredicate = true;
SeenPredMod = true;
}
if (!I->isPredicable())
return false;
}
return true;
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
/// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
@ -561,8 +603,7 @@ bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
MachineBasicBlock *BB = *I;
AnalyzeBlock(BB);
BBInfo &BBI = BBAnalysis[BB->getNumber()];
BBInfo &BBI = AnalyzeBlock(BB);
switch (BBI.Kind) {
case ICSimple:
case ICSimpleFalse:
@ -602,8 +643,10 @@ void IfConverter::ReTryPreds(MachineBasicBlock *BB) {
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI) {
BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
if (PBBI.Kind == ICNotClassfied)
PBBI.Kind = ICReAnalyze;
if (!PBBI.IsDone && PBBI.Kind == ICNotClassfied) {
assert(PBBI.IsEnqueued && "Unexpected");
PBBI.IsAnalyzed = false;
}
}
}
@ -672,12 +715,10 @@ bool IfConverter::IfConvertSimple(BBInfo &BBI) {
RemoveExtraEdges(BBI);
// Update block info. BB can be iteratively if-converted.
if (IterIfcvt)
BBI.Kind = ICReAnalyze;
else
BBI.Kind = ICDead;
if (!IterIfcvt)
BBI.IsDone = true;
ReTryPreds(BBI.BB);
CvtBBI->Kind = ICDead;
CvtBBI->IsDone = true;
// FIXME: Must maintain LiveIns.
return true;
@ -703,7 +744,8 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
if (PBB == BBI.BB)
continue;
BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
PBBI.Kind = ICReAnalyze;
if (PBBI.IsEnqueued)
PBBI.IsEnqueued = false;
}
}
std::swap(CvtBBI, NextBBI);
@ -751,14 +793,12 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
RemoveExtraEdges(BBI);
// Update block info. BB can be iteratively if-converted.
if (IterIfcvt)
BBI.Kind = ICReAnalyze;
else
BBI.Kind = ICDead;
if (!IterIfcvt)
BBI.IsDone = true;
ReTryPreds(BBI.BB);
CvtBBI->Kind = ICDead;
CvtBBI->IsDone = true;
if (FalseBBDead)
NextBBI->Kind = ICDead;
NextBBI->IsDone = true;
// FIXME: Must maintain LiveIns.
return true;
@ -822,8 +862,8 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
bool NeedBr1 = !BBI1->TrueBB && BBI1->BB->succ_size();
bool NeedBr2 = !BBI2->TrueBB && BBI2->BB->succ_size();
if ((TrueBBI.ModifyPredicate && !FalseBBI.ModifyPredicate) ||
(!TrueBBI.ModifyPredicate && !FalseBBI.ModifyPredicate &&
if ((TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred) ||
(!TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred &&
NeedBr1 && !NeedBr2)) {
std::swap(BBI1, BBI2);
std::swap(Cond1, Cond2);
@ -878,15 +918,13 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
MergeBlocks(*CvtBBI, TailBBI);
TailBBI.Kind = ICDead;
TailBBI.IsDone = true;
}
RemoveExtraEdges(BBI);
// Update block info.
BBI.Kind = ICDead;
TrueBBI.Kind = ICDead;
FalseBBI.Kind = ICDead;
BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
// FIXME: Must maintain LiveIns.
return true;
@ -953,7 +991,7 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
ToBBI.NonPredSize += FromBBI.NonPredSize;
FromBBI.NonPredSize = 0;
ToBBI.ModifyPredicate |= FromBBI.ModifyPredicate;
ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
ToBBI.HasFallThrough = FromBBI.HasFallThrough;
std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),