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Carefully remove extraneous CFG edges after each ifcvt.

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llvm-svn: 37529
This commit is contained in:
Evan Cheng 2007-06-08 22:01:07 +00:00
parent 1a6c0341fd
commit 7996fc5d23
1 changed files with 51 additions and 24 deletions
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75
lib/CodeGen/IfConversion.cpp
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@ -126,6 +126,7 @@ namespace {
bool AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates);
void ReTryPreds(MachineBasicBlock *BB);
void RemoveExtraEdges(BBInfo &BBI);
bool IfConvertSimple(BBInfo &BBI);
bool IfConvertTriangle(BBInfo &BBI);
bool IfConvertDiamond(BBInfo &BBI);
@ -542,9 +543,10 @@ bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
return Change;
}
/// 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) {
/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
/// that all the intervening blocks are empty (given BB can fall through to its
/// next block).
static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
MachineFunction::iterator I = BB;
MachineFunction::iterator TI = ToBB;
MachineFunction::iterator E = BB->getParent()->end();
@ -554,13 +556,24 @@ static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
return true;
}
/// getNextBlock - Returns the next block in the function blocks ordering. If
/// it is the end, returns NULL.
static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
MachineFunction::iterator I = BB;
MachineFunction::iterator E = BB->getParent()->end();
if (++I == E)
return NULL;
return I;
}
/// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
/// to determine if it can be if-converted.
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()];
PBBI.Kind = ICReAnalyze;
if (PBBI.Kind == ICNotClassfied)
PBBI.Kind = ICReAnalyze;
}
}
@ -572,6 +585,23 @@ static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
TII->InsertBranch(*BB, ToBB, NULL, NoCond);
}
/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
/// successors.
void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
MachineBasicBlock *TBB = NULL, *FBB = NULL;
std::vector<MachineOperand> Cond;
bool isAnalyzable = !TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond);
bool CanFallthrough = isAnalyzable && (TBB == NULL || FBB == NULL);
if (BBI.TrueBB && BBI.BB->isSuccessor(BBI.TrueBB))
if (!(BBI.TrueBB == TBB || BBI.TrueBB == FBB ||
(CanFallthrough && getNextBlock(BBI.BB) == BBI.TrueBB)))
BBI.BB->removeSuccessor(BBI.TrueBB);
if (BBI.FalseBB && BBI.BB->isSuccessor(BBI.FalseBB))
if (!(BBI.FalseBB == TBB || BBI.FalseBB == FBB ||
(CanFallthrough && getNextBlock(BBI.BB) == BBI.FalseBB)))
BBI.BB->removeSuccessor(BBI.FalseBB);
}
/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
///
bool IfConverter::IfConvertSimple(BBInfo &BBI) {
@ -588,14 +618,12 @@ bool IfConverter::IfConvertSimple(BBInfo &BBI) {
PredicateBlock(*CvtBBI, Cond);
// Merge converted block into entry block. Also add an unconditional branch
// to the 'false' branch.
// Merge converted block into entry block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
BBI.BB->removeSuccessor(CvtBBI->BB);
bool IterIfcvt = true;
if (!isNextBlock(BBI.BB, NextBBI->BB)) {
if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
BBI.hasFallThrough = false;
// Now ifcvt'd block will look like this:
@ -611,6 +639,8 @@ bool IfConverter::IfConvertSimple(BBInfo &BBI) {
IterIfcvt = false;
}
RemoveExtraEdges(BBI);
// Update block info. BB can be iteratively if-converted.
if (IterIfcvt)
BBI.Kind = ICReAnalyze;
@ -650,7 +680,7 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
bool FalseBBDead = false;
bool IterIfcvt = true;
bool isFallThrough = isNextBlock(BBI.BB, FalseBBI.BB);
bool isFallThrough = canFallThroughTo(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
@ -667,9 +697,7 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
IterIfcvt = false;
}
// Remove entry to false edge if false block is merged in as well.
if (FalseBBDead)
BBI.BB->removeSuccessor(FalseBBI.BB);
RemoveExtraEdges(BBI);
// Update block info. BB can be iteratively if-converted.
if (IterIfcvt)
@ -767,7 +795,7 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
if (NeedBr2 && !NeedBr1) {
// If BBI2 isn't going to be merged in, then the existing fallthrough
// or branch is fine.
if (!isNextBlock(BBI.BB, *BBI2->BB->succ_begin())) {
if (!canFallThroughTo(BBI.BB, *BBI2->BB->succ_begin())) {
InsertUncondBranch(BBI2->BB, *BBI2->BB->succ_begin(), TII);
BBI2->hasFallThrough = false;
}
@ -785,7 +813,7 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
// 'True' and 'false' aren't combined, see if we need to add a unconditional
// branch to the 'false' block.
if (NeedBr1 && !isNextBlock(BBI.BB, BBI2->BB)) {
if (NeedBr1 && !canFallThroughTo(BBI.BB, BBI2->BB)) {
InsertUncondBranch(BBI.BB, BBI2->BB, TII);
BBI1->hasFallThrough = false;
}
@ -802,6 +830,8 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
TailBBI.Kind = ICDead;
}
RemoveExtraEdges(BBI);
// Update block info.
BBI.Kind = ICDead;
TrueBBI.Kind = ICDead;
@ -834,14 +864,6 @@ void IfConverter::PredicateBlock(BBInfo &BBI,
NumIfConvBBs++;
}
static MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
MachineFunction::iterator I = BB;
MachineFunction::iterator E = BB->getParent()->end();
if (++I == E)
return NULL;
return I;
}
/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
///
void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
@ -860,11 +882,12 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
FromBBI.BB->succ_end());
MachineBasicBlock *FallThrough = FromBBI.hasFallThrough
? getNextBlock(FromBBI.BB) : NULL;
MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
MachineBasicBlock *FallThrough = FromBBI.hasFallThrough ? NBB : NULL;
for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
MachineBasicBlock *Succ = Succs[i];
// Fallthrough edge can't be transferred.
if (Succ == FallThrough)
continue;
FromBBI.BB->removeSuccessor(Succ);
@ -872,6 +895,10 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
ToBBI.BB->addSuccessor(Succ);
}
// Now FromBBI always fall through to the next block!
if (NBB)
FromBBI.BB->addSuccessor(NBB);
ToBBI.NonPredSize += FromBBI.NonPredSize;
FromBBI.NonPredSize = 0;