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Let IfConverter loose. Allow more aggressive subsumptions; reorder basic blocks to expose more ifcvt opportunities; code clean up and fixes.

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llvm-svn: 37409
This commit is contained in:
Evan Cheng 2007-06-04 06:47:22 +00:00
parent 0dbe4d04db
commit c86e3086da
1 changed files with 264 additions and 196 deletions
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460
lib/CodeGen/IfConversion.cpp
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@ -24,6 +24,10 @@
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumSimple, "Number of simple if-conversions performed");
STATISTIC(NumSimpleRev, "Number of simple (reversed) if-conversions performed");
STATISTIC(NumTriangle, "Number of triangle if-conversions performed");
STATISTIC(NumDiamonds, "Number of diamond if-conversions performed");
STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
namespace {
@ -32,8 +36,8 @@ namespace {
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.
ICEarlyExitFalse,// Same as ICEarlyExit, but on the false path.
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.
ICDiamond, // BB is entry of a diamond sub-CFG.
ICChild, // BB is part of the sub-CFG that'll be predicated.
@ -49,8 +53,7 @@ namespace {
///
/// 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.
/// IsAnalyzable - True if AnalyzeBranch() returns false.
/// ModifyPredicate - FIXME: Not used right now. True if BB would modify
/// the predicate (e.g. has cmp, call, etc.)
/// BB - Corresponding MachineBasicBlock.
@ -60,8 +63,7 @@ namespace {
struct BBInfo {
BBICKind Kind;
unsigned NonPredSize;
bool isPredicable;
bool hasEarlyExit;
bool IsAnalyzable;
bool ModifyPredicate;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
@ -69,8 +71,8 @@ namespace {
MachineBasicBlock *TailBB;
std::vector<MachineOperand> BrCond;
std::vector<MachineOperand> Predicate;
BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0), isPredicable(false),
hasEarlyExit(false), ModifyPredicate(false),
BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0),
IsAnalyzable(false), ModifyPredicate(false),
BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
};
@ -93,14 +95,16 @@ namespace {
virtual const char *getPassName() const { return "If converter"; }
private:
bool ReverseBranchCondition(BBInfo &BBI);
void StructuralAnalysis(MachineBasicBlock *BB);
void FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond);
bool FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm = false);
bool AttemptRestructuring(BBInfo &BBI);
bool AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates);
void ReTryPreds(MachineBasicBlock *BB);
bool IfConvertEarlyExit(BBInfo &BBI);
bool IfConvertSimple(BBInfo &BBI);
bool IfConvertTriangle(BBInfo &BBI);
bool IfConvertDiamond(BBInfo &BBI);
void PredicateBlock(BBInfo &BBI,
@ -137,39 +141,49 @@ bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
std::vector<BBInfo*> Candidates;
MadeChange = false;
while (true) {
bool Change = false;
// Do an intial analysis for each basic block and finding all the potential
// candidates to perform if-convesion.
Change |= AnalyzeBlocks(MF, Candidates);
bool Change = AnalyzeBlocks(MF, Candidates);
while (!Candidates.empty()) {
BBInfo &BBI = *Candidates.back();
Candidates.pop_back();
bool RetVal = false;
switch (BBI.Kind) {
default: assert(false && "Unexpected!");
break;
case ICReAnalyze:
// One or more of 'childrean' have been modified, abort!
break;
case ICEarlyExit:
case ICEarlyExitFalse:
DOUT << "Ifcvt (Early exit): BB#" << BBI.BB->getNumber() << "\n";
Change |= IfConvertEarlyExit(BBI);
break;
case ICSimple:
case ICSimpleFalse:
DOUT << "Ifcvt (Simple" << (BBI.Kind == ICSimpleFalse ? " false" : "")
<< "): BB#" << BBI.BB->getNumber() << " ";
RetVal = IfConvertSimple(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal)
if (BBI.Kind == ICSimple) NumSimple++;
else NumSimpleRev++;
break;
case ICTriangle:
DOUT << "Ifcvt (Triangle): BB#" << BBI.BB->getNumber() << "\n";
Change |= IfConvertTriangle(BBI);
DOUT << "Ifcvt (Triangle): BB#" << BBI.BB->getNumber() << " ";
RetVal = IfConvertTriangle(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal) NumTriangle++;
break;
case ICDiamond:
DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << "\n";
Change |= IfConvertDiamond(BBI);
DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " ";
RetVal = IfConvertDiamond(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal) NumDiamonds++;
break;
}
Change |= RetVal;
}
MadeChange |= Change;
if (!Change)
break;
MadeChange |= Change;
}
Roots.clear();
@ -189,13 +203,25 @@ static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
return NULL;
}
bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
if (!TII->ReverseBranchCondition(BBI.BrCond)) {
TII->RemoveBranch(*BBI.BB);
TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
std::swap(BBI.TrueBB, BBI.FalseBB);
return true;
}
return false;
}
/// 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 != ICReAnalyze) {
if (BBI.Kind == ICReAnalyze)
BBI.BrCond.clear();
else {
if (BBI.Kind != ICNotAnalyzed)
return; // Already analyzed.
BBI.BB = BB;
@ -204,57 +230,64 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
// 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)
BBI.IsAnalyzable =
!TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
if (!BBI.IsAnalyzable || BBI.BrCond.size() == 0)
return;
// Not a candidate if 'true' block is going to be if-converted.
StructuralAnalysis(BBI.TrueBB);
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
// TODO: Only handle very simple cases for now.
if (TrueBBI.FalseBB || TrueBBI.BrCond.size())
return;
// 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!");
// Not a candidate if 'false' block is going to be if-converted.
StructuralAnalysis(BBI.FalseBB);
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
// TODO: Only handle very simple cases for now.
if (FalseBBI.FalseBB || FalseBBI.BrCond.size())
return;
unsigned TrueNumPreds = BBI.TrueBB->pred_size();
unsigned FalseNumPreds = BBI.FalseBB->pred_size();
if ((TrueBBI.hasEarlyExit && TrueNumPreds <= 1) &&
!(FalseBBI.hasEarlyExit && FalseNumPreds <=1)) {
BBI.Kind = ICEarlyExit;
TrueBBI.Kind = ICChild;
} else if (!(TrueBBI.hasEarlyExit && TrueNumPreds <= 1) &&
(FalseBBI.hasEarlyExit && FalseNumPreds <=1)) {
BBI.Kind = ICEarlyExitFalse;
FalseBBI.Kind = ICChild;
} else if (TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB) {
// Triangle:
// EBB
// | \_
// | |
// | TBB
// | /
// FBB
BBI.Kind = ICTriangle;
TrueBBI.Kind = FalseBBI.Kind = ICChild;
} else if (TrueBBI.TrueBB == FalseBBI.TrueBB &&
TrueNumPreds <= 1 && FalseNumPreds <= 1) {
// 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 (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 (TrueBBI.TrueBB == FalseBBI.TrueBB && CanRevCond &&
TrueBBI.BB->pred_size() == 1 &&
TrueBBI.BB->pred_size() == 1 &&
// Check the 'true' and 'false' blocks if either isn't ended with
// a branch. If the block does not fallthrough to another block
// then we need to add a branch to its successor.
!(TrueBBI.ModifyPredicate &&
!TrueBBI.TrueBB && TrueBBI.BB->succ_size()) &&
!(FalseBBI.ModifyPredicate &&
!FalseBBI.TrueBB && FalseBBI.BB->succ_size()) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
// EBB
// / \_
@ -266,6 +299,44 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
BBI.Kind = ICDiamond;
TrueBBI.Kind = FalseBBI.Kind = ICChild;
BBI.TailBB = TrueBBI.TrueBB;
} else {
// FIXME: Consider duplicating if BB is small.
bool TryTriangle = TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB &&
BBI.TrueBB->pred_size() == 1;
bool TrySimple = TrueBBI.BrCond.size() == 0 && BBI.TrueBB->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 && BBI.FalseBB->pred_size() == 1) {
// Try 'simple' on the other path...
std::vector<MachineOperand> RevCond(BBI.BrCond);
if (TII->ReverseBranchCondition(RevCond))
assert(false && "Unable to reverse branch condition!");
if (FeasibilityAnalysis(FalseBBI, RevCond)) {
BBI.Kind = ICSimpleFalse;
FalseBBI.Kind = ICChild;
}
}
}
return;
}
@ -274,25 +345,37 @@ 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. Note, this function assumes
/// all the terminator instructions can be converted or deleted so it ignore
/// them.
void IfConverter::FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond) {
/// predicable unless it's the last instruction. If IgnoreTerm is true then
/// all the terminator instructions are skipped.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm) {
// 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;
return false;
// If it is already predicated, check if its predicate subsumes the new
// predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
return false;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
continue;
// TODO: check if instruction clobbers predicate.
if (!I->isPredicable())
return;
return false;
}
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
return;
BBI.isPredicable = true;
return true;
}
/// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
@ -336,8 +419,8 @@ bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
StructuralAnalysis(BB);
BBInfo &BBI = BBAnalysis[BB->getNumber()];
switch (BBI.Kind) {
case ICEarlyExit:
case ICEarlyExitFalse:
case ICSimple:
case ICSimpleFalse:
case ICTriangle:
case ICDiamond:
Candidates.push_back(&BBI);
@ -355,37 +438,14 @@ bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
return Change;
}
/// TransferPreds - Transfer all the predecessors of FromBB to ToBB.
///
static void TransferPreds(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
std::vector<MachineBasicBlock*> Preds(FromBB->pred_begin(),
FromBB->pred_end());
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
MachineBasicBlock *Pred = Preds[i];
Pred->removeSuccessor(FromBB);
if (!Pred->isSuccessor(ToBB))
Pred->addSuccessor(ToBB);
}
}
/// TransferSuccs - Transfer all the successors of FromBB to ToBB.
///
static void TransferSuccs(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
std::vector<MachineBasicBlock*> Succs(FromBB->succ_begin(),
FromBB->succ_end());
for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
MachineBasicBlock *Succ = Succs[i];
FromBB->removeSuccessor(Succ);
if (!ToBB->isSuccessor(Succ))
ToBB->addSuccessor(Succ);
}
}
/// isNextBlock - Returns true if ToBB the next basic block after BB.
///
/// isNextBlock - Returns true either if ToBB the next block after BB or
/// that all the intervening blocks are empty.
static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
MachineFunction::iterator Fallthrough = BB;
return MachineFunction::iterator(ToBB) == ++Fallthrough;
MachineFunction::iterator I = BB;
while (++I != MachineFunction::iterator(ToBB))
if (!I->empty())
return false;
return true;
}
/// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
@ -406,10 +466,10 @@ static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
TII->InsertBranch(*BB, ToBB, NULL, NoCond);
}
/// IfConvertEarlyExit - If convert a early exit sub-CFG.
/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
///
bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
bool ReverseCond = BBI.Kind == ICEarlyExitFalse;
bool IfConverter::IfConvertSimple(BBInfo &BBI) {
bool ReverseCond = BBI.Kind == ICSimpleFalse;
BBI.Kind = ICNotClassfied;
@ -418,25 +478,29 @@ bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
BBInfo *CvtBBI = &TrueBBI;
BBInfo *NextBBI = &FalseBBI;
std::vector<MachineOperand> NewCond(BBI.BrCond);
std::vector<MachineOperand> Cond(BBI.BrCond);
if (ReverseCond) {
std::swap(CvtBBI, NextBBI);
TII->ReverseBranchCondition(NewCond);
TII->ReverseBranchCondition(Cond);
}
FeasibilityAnalysis(*CvtBBI, NewCond);
if (!CvtBBI->isPredicable)
return false;
PredicateBlock(*CvtBBI, NewCond);
PredicateBlock(*CvtBBI, Cond);
// If the 'true' block ends without a branch, add a conditional branch
// to its successor unless that happens to be the 'false' block.
if (CvtBBI->IsAnalyzable && CvtBBI->TrueBB == NULL) {
assert(CvtBBI->BB->succ_size() == 1 && "Unexpected!");
MachineBasicBlock *SuccBB = *CvtBBI->BB->succ_begin();
if (SuccBB != NextBBI->BB)
TII->InsertBranch(*CvtBBI->BB, SuccBB, NULL, Cond);
}
// Merge converted block into entry block. Also convert the end of the
// block conditional branch (to the non-converted block) into an
// unconditional one.
// Merge converted block into entry block. Also add an unconditional branch
// to the 'false' branch.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
if (!isNextBlock(BBI.BB, NextBBI->BB))
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
std::copy(NewCond.begin(), NewCond.end(), std::back_inserter(BBI.Predicate));
std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
// Update block info. BB can be iteratively if-converted.
BBI.Kind = ICNotAnalyzed;
@ -447,7 +511,6 @@ bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
CvtBBI->Kind = ICDead;
// FIXME: Must maintain LiveIns.
NumIfConvBBs++;
return true;
}
@ -457,19 +520,12 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
BBI.Kind = ICNotClassfied;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
FeasibilityAnalysis(TrueBBI, BBI.BrCond);
if (!TrueBBI.isPredicable)
return false;
// FIXME: Consider duplicating if BB is small.
if (BBI.TrueBB->pred_size() > 1)
return false;
// Predicate the 'true' block after removing its branch.
TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(TrueBBI, BBI.BrCond);
// If 'true' block has a 'false' successor, add a early exit branch to it.
// If 'true' block has a 'false' successor, add an exit branch to it.
if (TrueBBI.FalseBB) {
std::vector<MachineOperand> RevCond(TrueBBI.BrCond);
if (TII->ReverseBranchCondition(RevCond))
@ -482,7 +538,7 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
if (FalseBBI.BB->pred_size() == 2)
MergeBlocks(TrueBBI, FalseBBI);
else
else if (!isNextBlock(TrueBBI.BB, FalseBBI.BB))
InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
// Now merge the entry of the triangle with the true block.
@ -500,7 +556,6 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
TrueBBI.Kind = ICDead;
// FIXME: Must maintain LiveIns.
NumIfConvBBs++;
return true;
}
@ -509,87 +564,66 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
BBI.Kind = ICNotClassfied;
bool TrueNeedBr;
bool FalseNeedBr;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
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;
if (Proceed) {
// 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 branch to its successor.
TrueNeedBr = !TrueBBI.TrueBB && BBI.TrueBB->succ_size();
FalseNeedBr = !FalseBBI.TrueBB && BBI.FalseBB->succ_size();
if (TrueNeedBr && TrueBBI.ModifyPredicate) {
TrueBBI.isPredicable = false;
Proceed = false;
}
if (FalseNeedBr && FalseBBI.ModifyPredicate) {
FalseBBI.isPredicable = false;
Proceed = false;
if (!BBI.TailBB) {
// No common merge block. Check if the terminators (e.g. return) are
// the same or predicable.
MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
if (TT->isIdenticalTo(FT))
Dups.push_back(TT); // Will erase these later.
else if (!TT->isPredicable() && !FT->isPredicable())
return false; // Can't if-convert. Abort!
++TT;
++FT;
}
if (Proceed) {
if (!BBI.TailBB) {
// No common merge block. Check if the terminators (e.g. return) are
// the same or predicable.
MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
if (TT->isIdenticalTo(FT))
Dups.push_back(TT); // Will erase these later.
else if (!TT->isPredicable() && !FT->isPredicable()) {
Proceed = false;
break; // Can't if-convert. Abort!
}
++TT;
++FT;
}
// One of the two pathes have more terminators, make sure they are
// all predicable.
while (Proceed && TT != BBI.TrueBB->end())
if (!TT->isPredicable()) {
Proceed = false;
break; // Can't if-convert. Abort!
}
while (Proceed && FT != BBI.FalseBB->end())
if (!FT->isPredicable()) {
Proceed = false;
break; // Can't if-convert. Abort!
}
// One of the two pathes have more terminators, make sure they are
// all predicable.
while (TT != BBI.TrueBB->end()) {
if (!TT->isPredicable()) {
return false; // Can't if-convert. Abort!
}
++TT;
}
while (FT != BBI.FalseBB->end()) {
if (!FT->isPredicable()) {
return false; // Can't if-convert. Abort!
}
++FT;
}
}
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.NonPredSize;
}
// Predicate the 'true' block after removing its branch.
TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(TrueBBI, BBI.BrCond);
// Predicate the 'false' block.
PredicateBlock(FalseBBI, RevCond, true);
// 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 branch to its successor.
bool TrueNeedBr = !TrueBBI.TrueBB && BBI.TrueBB->succ_size();
bool FalseNeedBr = !FalseBBI.TrueBB && BBI.FalseBB->succ_size();
// 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.
std::vector<MachineOperand> RevCond(BBI.BrCond);
TII->ReverseBranchCondition(RevCond);
BBInfo *CvtBBI;
if (!TrueBBI.ModifyPredicate) {
// Add a conditional branch from 'true' to 'true' successor if needed.
// Predicate the 'true' block after removing its branch.
TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(TrueBBI, BBI.BrCond);
// Predicate the 'false' block.
PredicateBlock(FalseBBI, RevCond, true);
if (TrueNeedBr)
TII->InsertBranch(*BBI.TrueBB, *BBI.TrueBB->succ_begin(), NULL,
BBI.BrCond);
@ -601,6 +635,13 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
MergeBlocks(TrueBBI, FalseBBI);
CvtBBI = &TrueBBI;
} else {
// Predicate the 'false' block after removing its branch.
FalseBBI.NonPredSize -= TII->RemoveBranch(*BBI.FalseBB);
PredicateBlock(FalseBBI, RevCond);
// Predicate the 'false' block.
PredicateBlock(TrueBBI, BBI.BrCond, true);
// Add a conditional branch from 'false' to 'false' successor if needed.
if (FalseNeedBr)
TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,
@ -625,7 +666,7 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
MergeBlocks(BBI, *CvtBBI);
CvtBBI = &BBI;
OkToIfcvt = false;
} else
} else if (!isNextBlock(BBI.BB, CvtBBI->BB))
InsertUncondBranch(BBI.BB, CvtBBI->BB, TII);
// If the if-converted block fallthrough or unconditionally branch into the
@ -651,7 +692,6 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
FalseBBI.Kind = ICDead;
// FIXME: Must maintain LiveIns.
NumIfConvBBs += 2;
return true;
}
@ -662,18 +702,41 @@ void IfConverter::PredicateBlock(BBInfo &BBI,
bool IgnoreTerm) {
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
MachineInstr *MI = I;
if (IgnoreTerm && TII->isTerminatorInstr(MI->getOpcode()))
if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
continue;
if (TII->isPredicated(MI))
if (TII->isPredicated(I))
continue;
if (!TII->PredicateInstruction(MI, Cond)) {
if (!TII->PredicateInstruction(I, Cond)) {
cerr << "Unable to predicate " << *I << "!\n";
abort();
}
}
BBI.NonPredSize = 0;
NumIfConvBBs++;
}
/// TransferPreds - Transfer all the predecessors of FromBB to ToBB.
///
static void TransferPreds(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
for (MachineBasicBlock::pred_iterator I = FromBB->pred_begin(),
E = FromBB->pred_end(); I != E; ++I) {
MachineBasicBlock *Pred = *I;
Pred->removeSuccessor(FromBB);
if (!Pred->isSuccessor(ToBB))
Pred->addSuccessor(ToBB);
}
}
/// TransferSuccs - Transfer all the successors of FromBB to ToBB.
///
static void TransferSuccs(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
for (MachineBasicBlock::succ_iterator I = FromBB->succ_begin(),
E = FromBB->succ_end(); I != E; ++I) {
FromBB->removeSuccessor(*I);
if (!ToBB->isSuccessor(*I))
ToBB->addSuccessor(*I);
}
}
/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
@ -687,6 +750,11 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
if (ToBBI.BB->isSuccessor(FromBBI.BB))
ToBBI.BB->removeSuccessor(FromBBI.BB);
// Redirect all branches to FromBB to ToBB.
for (MachineBasicBlock::pred_iterator I = FromBBI.BB->pred_begin(),
E = FromBBI.BB->pred_end(); I != E; ++I)
(*I)->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
// Transfer preds / succs and update size.
TransferPreds(ToBBI.BB, FromBBI.BB);
TransferSuccs(ToBBI.BB, FromBBI.BB);