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Preliminary iterative if-conversion support.
llvm-svn: 37309
This commit is contained in:
Evan Cheng
parent
80122ab529
commit
3f44824179
@ -28,7 +28,8 @@ STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
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namespace {
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class IfConverter : public MachineFunctionPass {
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enum BBICKind {
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ICInvalid, // BB data invalid.
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ICNotAnalyzed, // BB has not been analyzed.
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ICReAnalyze, // BB must be re-analyzed.
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ICNotClassfied, // BB data valid, but not classified.
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ICEarlyExit, // BB is entry of an early-exit sub-CFG.
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ICTriangle, // BB is entry of a triangle sub-CFG.
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@ -43,19 +44,31 @@ namespace {
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/// classification, and common tail block of its successors (if it's a
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/// diamond shape), its size, whether it's predicable, and whether any
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/// instruction can clobber the 'would-be' predicate.
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///
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/// Kind - Type of block. See BBICKind.
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/// NonPredSize - Number of non-predicated instructions.
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/// isPredicable - Is it predicable. (FIXME: Remove.)
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/// hasEarlyExit - Ends with a return, indirect jump or br to jumptable.
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/// ModifyPredicate - FIXME: Not used right now. True if BB would modify
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/// the predicate (e.g. has cmp, call, etc.)
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/// BB - Corresponding MachineBasicBlock.
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/// TrueBB / FalseBB- See AnalyzeBranch().
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/// BrCond - Conditions for end of block conditional branches.
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/// Predicate - Predicate used in the BB.
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struct BBInfo {
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BBICKind Kind;
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unsigned Size;
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unsigned NonPredSize;
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bool isPredicable;
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bool ClobbersPred;
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bool hasEarlyExit;
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bool ModifyPredicate;
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MachineBasicBlock *BB;
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MachineBasicBlock *TrueBB;
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MachineBasicBlock *FalseBB;
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MachineBasicBlock *TailBB;
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std::vector<MachineOperand> Cond;
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BBInfo() : Kind(ICInvalid), Size(0), isPredicable(false),
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ClobbersPred(false), hasEarlyExit(false),
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std::vector<MachineOperand> BrCond;
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std::vector<MachineOperand> Predicate;
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BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0), isPredicable(false),
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hasEarlyExit(false), ModifyPredicate(false),
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BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
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};
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@ -75,13 +88,15 @@ namespace {
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private:
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void StructuralAnalysis(MachineBasicBlock *BB);
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void FeasibilityAnalysis(BBInfo &BBI);
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void InitialFunctionAnalysis(MachineFunction &MF,
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std::vector<BBInfo*> &Candidates);
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void FeasibilityAnalysis(BBInfo &BBI,
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std::vector<MachineOperand> &Cond);
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void AnalyzeBlocks(MachineFunction &MF,
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std::vector<BBInfo*> &Candidates);
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void InvalidatePreds(MachineBasicBlock *BB);
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bool IfConvertEarlyExit(BBInfo &BBI);
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bool IfConvertTriangle(BBInfo &BBI);
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bool IfConvertDiamond(BBInfo &BBI);
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void PredicateBlock(MachineBasicBlock *BB,
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void PredicateBlock(BBInfo &BBI,
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std::vector<MachineOperand> &Cond,
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bool IgnoreTerm = false);
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void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI);
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@ -101,26 +116,34 @@ bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
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BBAnalysis.resize(NumBBs);
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std::vector<BBInfo*> Candidates;
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// Do an intial analysis for each basic block and finding all the potential
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// candidates to perform if-convesion.
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InitialFunctionAnalysis(MF, Candidates);
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MadeChange = false;
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for (unsigned i = 0, e = Candidates.size(); i != e; ++i) {
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BBInfo &BBI = *Candidates[i];
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switch (BBI.Kind) {
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default: assert(false && "Unexpected!");
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break;
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case ICEarlyExit:
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MadeChange |= IfConvertEarlyExit(BBI);
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break;
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case ICTriangle:
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MadeChange |= IfConvertTriangle(BBI);
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break;
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case ICDiamond:
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MadeChange |= IfConvertDiamond(BBI);
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break;
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while (true) {
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bool Change = false;
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// Do an intial analysis for each basic block and finding all the potential
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// candidates to perform if-convesion.
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AnalyzeBlocks(MF, Candidates);
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while (!Candidates.empty()) {
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BBInfo &BBI = *Candidates.back();
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Candidates.pop_back();
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switch (BBI.Kind) {
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default: assert(false && "Unexpected!");
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break;
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case ICEarlyExit:
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Change |= IfConvertEarlyExit(BBI);
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break;
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case ICTriangle:
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Change |= IfConvertTriangle(BBI);
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break;
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case ICDiamond:
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Change |= IfConvertDiamond(BBI);
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break;
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}
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}
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MadeChange |= Change;
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if (!Change)
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break;
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}
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BBAnalysis.clear();
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@ -145,18 +168,21 @@ static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
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void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
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BBInfo &BBI = BBAnalysis[BB->getNumber()];
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if (BBI.Kind != ICInvalid)
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return; // Already analyzed.
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BBI.BB = BB;
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BBI.Size = std::distance(BB->begin(), BB->end());
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if (BBI.Kind != ICReAnalyze) {
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if (BBI.Kind != ICNotAnalyzed)
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return; // Already analyzed.
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BBI.BB = BB;
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BBI.NonPredSize = std::distance(BB->begin(), BB->end());
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// Look for 'root' of a simple (non-nested) triangle or diamond.
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BBI.Kind = ICNotClassfied;
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bool CanAnalyze = !TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB, BBI.Cond);
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// Does it end with a return, indirect jump, or jumptable branch?
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BBI.hasEarlyExit = TII->BlockHasNoFallThrough(*BB) && !BBI.TrueBB;
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if (!CanAnalyze || !BBI.TrueBB || BBI.Cond.size() == 0)
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return;
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// Look for 'root' of a simple (non-nested) triangle or diamond.
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BBI.Kind = ICNotClassfied;
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bool CanAnalyze = !TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB,
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BBI.BrCond);
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// Does it end with a return, indirect jump, or jumptable branch?
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BBI.hasEarlyExit = TII->BlockHasNoFallThrough(*BB) && !BBI.TrueBB;
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if (!CanAnalyze || !BBI.TrueBB || BBI.BrCond.size() == 0)
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return;
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}
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// Not a candidate if 'true' block is going to be if-converted.
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StructuralAnalysis(BBI.TrueBB);
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@ -165,7 +191,7 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
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return;
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// TODO: Only handle very simple cases for now.
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if (TrueBBI.FalseBB || TrueBBI.Cond.size())
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if (TrueBBI.FalseBB || TrueBBI.BrCond.size())
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return;
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// No false branch. This BB must end with a conditional branch and a
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@ -181,7 +207,7 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
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return;
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// TODO: Only handle very simple cases for now.
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if (FalseBBI.FalseBB || FalseBBI.Cond.size())
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if (FalseBBI.FalseBB || FalseBBI.BrCond.size())
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return;
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unsigned TrueNumPreds = BBI.TrueBB->pred_size();
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@ -228,8 +254,9 @@ void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
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/// predicable unless it's the last instruction. Note, this function assumes
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/// all the terminator instructions can be converted or deleted so it ignore
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/// them.
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void IfConverter::FeasibilityAnalysis(BBInfo &BBI) {
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if (BBI.Size == 0 || BBI.Size > TLI->getIfCvtBlockSizeLimit())
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void IfConverter::FeasibilityAnalysis(BBInfo &BBI,
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std::vector<MachineOperand> &Cond) {
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if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
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return;
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for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
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@ -241,13 +268,16 @@ void IfConverter::FeasibilityAnalysis(BBInfo &BBI) {
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return;
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}
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if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
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return;
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BBI.isPredicable = true;
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}
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/// InitialFunctionAnalysis - Analyze all blocks and find entries for all
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/// AnalyzeBlocks - Analyze all blocks and find entries for all
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/// if-conversion candidates.
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void IfConverter::InitialFunctionAnalysis(MachineFunction &MF,
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std::vector<BBInfo*> &Candidates) {
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void IfConverter::AnalyzeBlocks(MachineFunction &MF,
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std::vector<BBInfo*> &Candidates) {
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std::set<MachineBasicBlock*> Visited;
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MachineBasicBlock *Entry = MF.begin();
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for (df_ext_iterator<MachineBasicBlock*> DFI = df_ext_begin(Entry, Visited),
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@ -299,42 +329,58 @@ static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
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return MachineFunction::iterator(ToBB) == ++Fallthrough;
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}
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/// InvalidatePreds - 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::InvalidatePreds(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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PBBI.Kind = ICReAnalyze;
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}
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}
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/// IfConvertEarlyExit - If convert a early exit sub-CFG.
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///
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bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
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BBI.Kind = ICNotClassfied;
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BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
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BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
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BBInfo *CvtBBI = &TrueBBI;
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BBInfo *NextBBI = &FalseBBI;
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bool ReserveCond = false;
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if (TrueBBI.Kind != ICChild) {
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std::swap(CvtBBI, NextBBI);
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ReserveCond = true;
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}
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FeasibilityAnalysis(*CvtBBI);
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if (!CvtBBI->isPredicable) {
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BBI.Kind = ICNotClassfied;
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return false;
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}
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std::vector<MachineOperand> NewCond(BBI.Cond);
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std::vector<MachineOperand> NewCond(BBI.BrCond);
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if (ReserveCond)
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TII->ReverseBranchCondition(NewCond);
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PredicateBlock(CvtBBI->BB, NewCond);
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FeasibilityAnalysis(*CvtBBI, NewCond);
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if (!CvtBBI->isPredicable)
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return false;
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PredicateBlock(*CvtBBI, NewCond);
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// Merge converted block into entry block. Also convert the end of the
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// block conditional branch (to the non-converted block) into an
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// unconditional one.
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BBI.Size -= TII->RemoveBranch(*BBI.BB);
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BBI.BB->removeSuccessor(CvtBBI->BB);
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BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
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MergeBlocks(BBI, *CvtBBI);
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if (!isNextBlock(BBI.BB, NextBBI->BB)) {
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std::vector<MachineOperand> NoCond;
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TII->InsertBranch(*BBI.BB, NextBBI->BB, NULL, NoCond);
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}
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std::copy(NewCond.begin(), NewCond.end(), std::back_inserter(BBI.Predicate));
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// Update block info.
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// Update block info. BB can be iteratively if-converted.
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BBI.Kind = ICNotAnalyzed;
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BBI.TrueBB = BBI.FalseBB = NULL;
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BBI.BrCond.clear();
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TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
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InvalidatePreds(BBI.BB);
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CvtBBI->Kind = ICDead;
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// FIXME: Must maintain LiveIns.
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@ -345,29 +391,33 @@ bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
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/// IfConvertTriangle - If convert a triangle sub-CFG.
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///
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bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
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BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
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FeasibilityAnalysis(TrueBBI);
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BBI.Kind = ICNotClassfied;
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if (!TrueBBI.isPredicable) {
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BBI.Kind = ICNotClassfied;
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BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
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FeasibilityAnalysis(TrueBBI, BBI.BrCond);
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if (!TrueBBI.isPredicable)
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return false;
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}
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// Predicate the 'true' block after removing its branch.
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TrueBBI.Size -= TII->RemoveBranch(*BBI.TrueBB);
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PredicateBlock(BBI.TrueBB, BBI.Cond);
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TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
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PredicateBlock(TrueBBI, BBI.BrCond);
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// Join the 'true' and 'false' blocks by copying the instructions
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// from the 'false' block to the 'true' block.
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BBI.TrueBB->removeSuccessor(BBI.FalseBB);
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BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
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MergeBlocks(TrueBBI, FalseBBI);
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// Now merge the entry of the triangle with the true block.
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BBI.Size -= TII->RemoveBranch(*BBI.BB);
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BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
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MergeBlocks(BBI, TrueBBI);
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std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
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std::back_inserter(BBI.Predicate));
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// Update block info.
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// Update block info. BB can be iteratively if-converted.
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BBI.Kind = ICNotClassfied;
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BBI.TrueBB = BBI.FalseBB = NULL;
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BBI.BrCond.clear();
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TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
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TrueBBI.Kind = ICDead;
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// FIXME: Must maintain LiveIns.
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@ -378,12 +428,16 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
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/// IfConvertDiamond - If convert a diamond sub-CFG.
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///
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bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
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BBI.Kind = ICNotClassfied;
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bool TrueNeedCBr;
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bool FalseNeedCBr;
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BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
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BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
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FeasibilityAnalysis(TrueBBI);
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FeasibilityAnalysis(FalseBBI);
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FeasibilityAnalysis(TrueBBI, BBI.BrCond);
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std::vector<MachineOperand> RevCond(BBI.BrCond);
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TII->ReverseBranchCondition(RevCond);
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FeasibilityAnalysis(FalseBBI, RevCond);
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SmallVector<MachineInstr*, 2> Dups;
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bool Proceed = TrueBBI.isPredicable && FalseBBI.isPredicable;
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@ -393,11 +447,11 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
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// return. If it's the former, add a conditional branch to its successor.
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TrueNeedCBr = !TrueBBI.TrueBB && BBI.TrueBB->succ_size();
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FalseNeedCBr = !FalseBBI.TrueBB && BBI.FalseBB->succ_size();
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if (TrueNeedCBr && TrueBBI.ClobbersPred) {
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if (TrueNeedCBr && TrueBBI.ModifyPredicate) {
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TrueBBI.isPredicable = false;
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Proceed = false;
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}
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if (FalseNeedCBr && FalseBBI.ClobbersPred) {
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if (FalseNeedCBr && FalseBBI.ModifyPredicate) {
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FalseBBI.isPredicable = false;
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Proceed = false;
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}
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@ -435,45 +489,42 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
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}
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}
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if (!Proceed) {
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BBI.Kind = ICNotClassfied;
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if (!Proceed)
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return false;
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}
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// Remove the duplicated instructions from the 'true' block.
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for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
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Dups[i]->eraseFromParent();
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--TrueBBI.Size;
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--TrueBBI.NonPredSize;
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}
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// Predicate the 'true' block after removing its branch.
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TrueBBI.Size -= TII->RemoveBranch(*BBI.TrueBB);
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PredicateBlock(BBI.TrueBB, BBI.Cond);
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TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
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PredicateBlock(TrueBBI, BBI.BrCond);
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// Add a conditional branch to 'true' successor if needed.
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if (TrueNeedCBr && TrueBBI.ClobbersPred &&
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if (TrueNeedCBr && TrueBBI.ModifyPredicate &&
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isNextBlock(BBI.TrueBB, *BBI.TrueBB->succ_begin()))
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TrueNeedCBr = false;
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if (TrueNeedCBr)
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TII->InsertBranch(*BBI.TrueBB, *BBI.TrueBB->succ_begin(), NULL, BBI.Cond);
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TII->InsertBranch(*BBI.TrueBB, *BBI.TrueBB->succ_begin(), NULL, BBI.BrCond);
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// Predicate the 'false' block.
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std::vector<MachineOperand> NewCond(BBI.Cond);
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TII->ReverseBranchCondition(NewCond);
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PredicateBlock(BBI.FalseBB, NewCond, true);
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PredicateBlock(FalseBBI, RevCond, true);
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// Add a conditional branch to 'false' successor if needed.
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if (FalseNeedCBr && !TrueBBI.ClobbersPred &&
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if (FalseNeedCBr && !TrueBBI.ModifyPredicate &&
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isNextBlock(BBI.FalseBB, *BBI.FalseBB->succ_begin()))
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FalseNeedCBr = false;
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if (FalseNeedCBr)
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TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,NewCond);
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TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,
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RevCond);
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// Merge the 'true' and 'false' blocks by copying the instructions
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// from the 'false' block to the 'true' block. That is, unless the true
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// block would clobber the predicate, in that case, do the opposite.
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BBInfo *CvtBBI;
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if (!TrueBBI.ClobbersPred) {
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if (!TrueBBI.ModifyPredicate) {
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MergeBlocks(TrueBBI, FalseBBI);
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CvtBBI = &TrueBBI;
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} else {
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@ -482,15 +533,16 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
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}
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// Remove the conditional branch from entry to the blocks.
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BBI.Size -= TII->RemoveBranch(*BBI.BB);
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BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
|
||||
|
||||
bool OkToIfcvt = true;
|
||||
// Merge the combined block into the entry of the diamond if the entry
|
||||
// block is its only predecessor. Otherwise, insert an unconditional
|
||||
// branch from entry to the if-converted block.
|
||||
if (CvtBBI->BB->pred_size() == 1) {
|
||||
BBI.BB->removeSuccessor(CvtBBI->BB);
|
||||
MergeBlocks(BBI, *CvtBBI);
|
||||
CvtBBI = &BBI;
|
||||
OkToIfcvt = false;
|
||||
} else {
|
||||
std::vector<MachineOperand> NoCond;
|
||||
TII->InsertBranch(*BBI.BB, CvtBBI->BB, NULL, NoCond);
|
||||
@ -499,14 +551,20 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
|
||||
// If the if-converted block fallthrough into the tail block, then
|
||||
// fold the tail block in as well.
|
||||
if (BBI.TailBB && CvtBBI->BB->succ_size() == 1) {
|
||||
CvtBBI->Size -= TII->RemoveBranch(*CvtBBI->BB);
|
||||
CvtBBI->BB->removeSuccessor(BBI.TailBB);
|
||||
CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
|
||||
BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
|
||||
MergeBlocks(*CvtBBI, TailBBI);
|
||||
TailBBI.Kind = ICDead;
|
||||
}
|
||||
|
||||
// Update block info.
|
||||
// Update block info. BB may be iteratively if-converted.
|
||||
if (OkToIfcvt) {
|
||||
BBI.Kind = ICNotClassfied;
|
||||
BBI.TrueBB = BBI.FalseBB = NULL;
|
||||
BBI.BrCond.clear();
|
||||
TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
|
||||
InvalidatePreds(BBI.BB);
|
||||
}
|
||||
TrueBBI.Kind = ICDead;
|
||||
FalseBBI.Kind = ICDead;
|
||||
|
||||
@ -517,18 +575,23 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
|
||||
|
||||
/// PredicateBlock - Predicate every instruction in the block with the specified
|
||||
/// condition. If IgnoreTerm is true, skip over all terminator instructions.
|
||||
void IfConverter::PredicateBlock(MachineBasicBlock *BB,
|
||||
void IfConverter::PredicateBlock(BBInfo &BBI,
|
||||
std::vector<MachineOperand> &Cond,
|
||||
bool IgnoreTerm) {
|
||||
for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
|
||||
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
|
||||
I != E; ++I) {
|
||||
if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
|
||||
MachineInstr *MI = I;
|
||||
if (IgnoreTerm && TII->isTerminatorInstr(MI->getOpcode()))
|
||||
continue;
|
||||
if (!TII->PredicateInstruction(&*I, Cond)) {
|
||||
if (TII->isPredicated(MI))
|
||||
continue;
|
||||
if (!TII->PredicateInstruction(MI, Cond)) {
|
||||
cerr << "Unable to predication " << *I << "!\n";
|
||||
abort();
|
||||
}
|
||||
}
|
||||
|
||||
BBI.NonPredSize = 0;
|
||||
}
|
||||
|
||||
/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
|
||||
@ -536,8 +599,15 @@ void IfConverter::PredicateBlock(MachineBasicBlock *BB,
|
||||
void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
|
||||
ToBBI.BB->splice(ToBBI.BB->end(),
|
||||
FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
|
||||
|
||||
// If FromBBI is previously a successor, remove it from ToBBI's successor
|
||||
// list and update its TrueBB / FalseBB field if needed.
|
||||
if (ToBBI.BB->isSuccessor(FromBBI.BB))
|
||||
ToBBI.BB->removeSuccessor(FromBBI.BB);
|
||||
|
||||
// Transfer preds / succs and update size.
|
||||
TransferPreds(ToBBI.BB, FromBBI.BB);
|
||||
TransferSuccs(ToBBI.BB, FromBBI.BB);
|
||||
ToBBI.Size += FromBBI.Size;
|
||||
FromBBI.Size = 0;
|
||||
ToBBI.NonPredSize += FromBBI.NonPredSize;
|
||||
FromBBI.NonPredSize = 0;
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue
Block a user