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Allow more cmp / bcc to be predicated; clean up triangle ifcvt checking code. 

llvm-svn: 37518
This commit is contained in:
Evan Cheng 2007-06-08 09:36:04 +00:00
parent 6740da9407
commit 7783f82e21
1 changed files with 135 additions and 144 deletions
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279
llvm/lib/CodeGen/IfConversion.cpp
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@ -98,13 +98,14 @@ namespace {
private:
bool ReverseBranchCondition(BBInfo &BBI);
bool BlockModifyPredicate(MachineBasicBlock *BB) const;
bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI) const;
bool ValidSimple(BBInfo &TrueBBI) const;
bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch = false) const;
bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const;
void StructuralAnalysis(MachineBasicBlock *BB);
bool FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm = false);
void ScanInstructions(BBInfo &BBI);
void AnalyzeBlock(MachineBasicBlock *BB);
bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond,
bool isTriangle = false, bool RevBranch = false);
bool AttemptRestructuring(BBInfo &BBI);
bool AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates);
@ -235,47 +236,44 @@ bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
return false;
}
/// BlockModifyPredicate - Returns true if any instruction in the block may
/// clobber the condition code or register(s) used to predicate instructions,
/// e.g. call, cmp.
bool IfConverter::BlockModifyPredicate(MachineBasicBlock *BB) const {
for (MachineBasicBlock::const_reverse_iterator I = BB->rbegin(),
E = BB->rend(); I != E; ++I)
if (I->getInstrDescriptor()->Flags & M_CLOBBERS_PRED)
return true;
return false;
/// ValidSimple - Returns true if the 'true' block (along with its
/// predecessor) forms a valid simple shape for ifcvt.
bool IfConverter::ValidSimple(BBInfo &TrueBBI) const {
return !blockAlwaysFallThrough(TrueBBI) &&
TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1;
}
/// ValidTriangle - Returns true if the 'true' and 'false' blocks paths (along
/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid triangle shape for ifcvt.
bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI) const {
bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch) const {
if (TrueBBI.BB->pred_size() != 1)
return false;
MachineBasicBlock *TTBB = TrueBBI.TrueBB;
if (!TTBB && blockAlwaysFallThrough(TrueBBI)) {
MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
MachineFunction::iterator I = TrueBBI.BB;
if (++I == TrueBBI.BB->getParent()->end())
return false;
TTBB = I;
TExit = I;
}
return TTBB && TTBB == FalseBBI.BB;
return TExit && TExit == FalseBBI.BB;
}
/// ValidDiamond - Returns true if the 'true' and 'false' blocks paths (along
/// 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 {
// FIXME: Also look for fallthrough
return (TrueBBI.TrueBB == FalseBBI.TrueBB &&
TrueBBI.BB->pred_size() == 1 &&
FalseBBI.BB->pred_size() == 1 &&
!(TrueBBI.ModifyPredicate && FalseBBI.ModifyPredicate) &&
!TrueBBI.FalseBB && !FalseBBI.FalseBB);
}
/// StructuralAnalysis - Analyze the structure of the sub-CFG starting from
/// 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::StructuralAnalysis(MachineBasicBlock *BB) {
void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.Kind == ICReAnalyze) {
@ -286,7 +284,6 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
return; // Already analyzed.
BBI.BB = BB;
BBI.NonPredSize = std::distance(BB->begin(), BB->end());
BBI.ModifyPredicate = BlockModifyPredicate(BB);
}
// Look for 'root' of a simple (non-nested) triangle or diamond.
@ -301,7 +298,7 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
if (BBI.TrueBB == BB || BBI.FalseBB == BB)
return;
StructuralAnalysis(BBI.TrueBB);
AnalyzeBlock(BBI.TrueBB);
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
// No false branch. This BB must end with a conditional branch and a
@ -310,7 +307,7 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
BBI.FalseBB = findFalseBlock(BB, BBI.TrueBB);
assert(BBI.FalseBB && "Expected to find the fallthrough block!");
StructuralAnalysis(BBI.FalseBB);
AnalyzeBlock(BBI.FalseBB);
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
// If both paths are dead, then forget about it.
@ -323,34 +320,11 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
// the CFG to form a triangle with the 'false' path.
std::vector<MachineOperand> RevCond(BBI.BrCond);
bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
if (FalseBBI.FalseBB) {
if (TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB)
return;
std::vector<MachineOperand> Cond(BBI.BrCond);
if (CanRevCond &&
FalseBBI.TrueBB && FalseBBI.BB->pred_size() == 1 &&
FeasibilityAnalysis(FalseBBI, RevCond, true)) {
std::vector<MachineOperand> FalseCond(FalseBBI.BrCond);
if (FalseBBI.TrueBB == BBI.TrueBB &&
TII->SubsumesPredicate(FalseCond, BBI.BrCond)) {
// Reverse 'true' and 'false' paths.
ReverseBranchCondition(BBI);
BBI.Kind = ICTriangle;
FalseBBI.Kind = ICChild;
} else if (FalseBBI.FalseBB == BBI.TrueBB &&
!TII->ReverseBranchCondition(FalseCond) &&
TII->SubsumesPredicate(FalseCond, BBI.BrCond)) {
// Reverse 'false' block's 'true' and 'false' paths and then
// reverse 'true' and 'false' paths.
ReverseBranchCondition(FalseBBI);
ReverseBranchCondition(BBI);
BBI.Kind = ICTriangle;
FalseBBI.Kind = ICChild;
}
}
} else if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) &&
!(TrueBBI.ModifyPredicate && FalseBBI.ModifyPredicate) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
// EBB
// / \_
@ -364,50 +338,46 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
BBI.TailBB = TrueBBI.TrueBB;
} else {
// FIXME: Consider duplicating if BB is small.
bool TryTriangle = ValidTriangle(TrueBBI, FalseBBI);
bool TrySimple = !blockAlwaysFallThrough(TrueBBI) &&
TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1;
if ((TryTriangle || TrySimple) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
if (TryTriangle) {
// Triangle:
// EBB
// | \_
// | |
// | TBB
// | /
// FBB
BBI.Kind = ICTriangle;
TrueBBI.Kind = ICChild;
} else {
// Simple (split, no rejoin):
// EBB
// | \_
// | |
// | TBB---> exit
// |
// FBB
BBI.Kind = ICSimple;
TrueBBI.Kind = ICChild;
}
} else if (FalseBBI.BrCond.size() == 0 && FalseBBI.BB->pred_size() == 1) {
if (ValidTriangle(TrueBBI, FalseBBI) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
// Triangle:
// EBB
// | \_
// | |
// | TBB
// | /
// FBB
BBI.Kind = ICTriangle;
TrueBBI.Kind = ICChild;
} else if (ValidSimple(TrueBBI) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
// Simple (split, no rejoin):
// EBB
// | \_
// | |
// | TBB---> exit
// |
// FBB
BBI.Kind = ICSimple;
TrueBBI.Kind = ICChild;
} else if (CanRevCond) {
// Try the other path...
bool TryTriangle = ValidTriangle(FalseBBI, TrueBBI);
bool TrySimple = !blockAlwaysFallThrough(FalseBBI);
if (TryTriangle || TrySimple) {
std::vector<MachineOperand> RevCond(BBI.BrCond);
if (!TII->ReverseBranchCondition(RevCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
if (TryTriangle) {
// Reverse 'true' and 'false' paths.
ReverseBranchCondition(BBI);
BBI.Kind = ICTriangle;
FalseBBI.Kind = ICChild;
} else {
BBI.Kind = ICSimpleFalse;
FalseBBI.Kind = ICChild;
}
}
if (ValidTriangle(FalseBBI, TrueBBI) &&
FeasibilityAnalysis(FalseBBI, RevCond, true)) {
// Reverse 'true' and 'false' paths.
ReverseBranchCondition(BBI);
BBI.Kind = ICTriangle;
FalseBBI.Kind = ICChild;
} else if (ValidTriangle(FalseBBI, TrueBBI, true) &&
FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
ReverseBranchCondition(FalseBBI);
ReverseBranchCondition(BBI);
BBI.Kind = ICTriangle;
FalseBBI.Kind = ICChild;
} else if (ValidSimple(FalseBBI) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
BBI.Kind = ICSimpleFalse;
FalseBBI.Kind = ICChild;
}
}
}
@ -418,11 +388,10 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
/// 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. If IgnoreTerm is true then
/// all the terminator instructions are skipped.
/// predicable unless it's the last instruction.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm) {
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 &&
@ -436,13 +405,46 @@ bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
// If it is already predicated, check if its predicate subsumes the new
// predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
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) {
if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
continue;
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;
}
@ -488,7 +490,7 @@ 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;
StructuralAnalysis(BB);
AnalyzeBlock(BB);
BBInfo &BBI = BBAnalysis[BB->getNumber()];
switch (BBI.Kind) {
case ICSimple:
@ -560,23 +562,23 @@ bool IfConverter::IfConvertSimple(BBInfo &BBI) {
// to the 'false' branch.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
BBI.BB->removeSuccessor(CvtBBI->BB);
bool IterIfcvt = true;
if (!isNextBlock(BBI.BB, NextBBI->BB)) {
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
BBI.hasFallThrough = false;
if (BBI.ModifyPredicate)
// Now ifcvt'd block will look like this:
// BB:
// ...
// t, f = cmp
// if t op
// b BBf
//
// We cannot further ifcvt this block because the unconditional branch
// will have to be predicated on the new condition, that will not be
// available if cmp executes.
IterIfcvt = false;
// Now ifcvt'd block will look like this:
// BB:
// ...
// t, f = cmp
// if t op
// b BBf
//
// We cannot further ifcvt this block because the unconditional branch
// will have to be predicated on the new condition, that will not be
// available if cmp executes.
IterIfcvt = false;
}
std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
@ -610,45 +612,34 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
TII->InsertBranch(*BBI.TrueBB, TrueBBI.FalseBB, NULL, RevCond);
}
// Join the 'true' and 'false' blocks if the 'false' block has no other
// predecessors. Otherwise, add a unconditional branch from 'true' to 'false'.
// Now merge the entry of the triangle with the true block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, TrueBBI);
// Merge in the 'false' block if the 'false' block has no other
// predecessors. Otherwise, add a unconditional branch from to 'false'.
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
bool FalseBBDead = false;
bool IterIfcvt = true;
bool isFallThrough = isNextBlock(TrueBBI.BB, FalseBBI.BB);
bool isFallThrough = isNextBlock(BBI.BB, FalseBBI.BB);
if (!isFallThrough) {
// Only merge them if the true block does not fallthrough to the false
// block. By not merging them, we make it possible to iteratively
// ifcvt the blocks.
if (!HasEarlyExit && FalseBBI.BB->pred_size() == 2) {
MergeBlocks(TrueBBI, FalseBBI);
if (!HasEarlyExit && FalseBBI.BB->pred_size() == 1) {
MergeBlocks(BBI, FalseBBI);
FalseBBDead = true;
// Mixed predicated and unpredicated code. This cannot be iteratively
// predicated.
IterIfcvt = false;
} else {
InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
InsertUncondBranch(BBI.BB, FalseBBI.BB, TII);
TrueBBI.hasFallThrough = false;
if (BBI.ModifyPredicate || TrueBBI.ModifyPredicate)
// Now ifcvt'd block will look like this:
// BB:
// ...
// t, f = cmp
// if t op
// b BBf
//
// We cannot further ifcvt this block because the unconditional branch will
// have to be predicated on the new condition, that will not be available
// if cmp executes.
IterIfcvt = false;
}
// Mixed predicated and unpredicated code. This cannot be iteratively
// predicated.
IterIfcvt = false;
}
// Now merge the entry of the triangle with the true block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, TrueBBI);
// Remove entry to false edge if false block is merged in as well.
if (FalseBBDead && BBI.BB->isSuccessor(FalseBBI.BB))
if (FalseBBDead)
BBI.BB->removeSuccessor(FalseBBI.BB);
std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
std::back_inserter(BBI.Predicate));