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