--- /dev/null
+//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by the Evan Cheng and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the machine instruction level if-conversion pass.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "ifconversion"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
+
+STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
+
+namespace {
+ class IfConverter : public MachineFunctionPass {
+ enum BBICKind {
+ ICInvalid, // BB data invalid.
+ ICNotClassfied, // BB data valid, but not classified.
+ ICTriangle, // BB is part of a triangle sub-CFG.
+ ICDiamond, // BB is part of a diamond sub-CFG.
+ ICTriangleEntry, // BB is entry of a triangle sub-CFG.
+ ICDiamondEntry // BB is entry of a diamond sub-CFG.
+ };
+
+ /// BBInfo - One per MachineBasicBlock, this is used to cache the result
+ /// if-conversion feasibility analysis. This includes results from
+ /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
+ /// classification, and common merge block of its successors (if it's a
+ /// diamond shape).
+ struct BBInfo {
+ BBICKind Kind;
+ MachineBasicBlock *EBB;
+ MachineBasicBlock *TBB;
+ MachineBasicBlock *FBB;
+ MachineBasicBlock *CMBB;
+ std::vector<MachineOperand> Cond;
+ BBInfo() : Kind(ICInvalid), EBB(0), TBB(0), FBB(0), CMBB(0) {}
+ };
+
+ /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
+ /// basic block number.
+ std::vector<BBInfo> BBAnalysis;
+
+ const TargetInstrInfo *TII;
+ bool MadeChange;
+ public:
+ static char ID;
+ IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
+
+ virtual bool runOnMachineFunction(MachineFunction &MF);
+ virtual const char *getPassName() const { return "If converter"; }
+
+ private:
+ void AnalyzeBlock(MachineBasicBlock *BB);
+ void InitialFunctionAnalysis(MachineFunction &MF,
+ std::vector<int> &Candidates);
+ bool IfConvertDiamond(BBInfo &BBI);
+ bool IfConvertTriangle(BBInfo &BBI);
+ bool isBlockPredicatable(MachineBasicBlock *BB,
+ bool IgnoreTerm = false) const;
+ void PredicateBlock(MachineBasicBlock *BB,
+ std::vector<MachineOperand> &Cond,
+ bool IgnoreTerm = false);
+ void MergeBlocks(MachineBasicBlock *TBB, MachineBasicBlock *FBB);
+ };
+ char IfConverter::ID = 0;
+}
+
+FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
+
+bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
+ TII = MF.getTarget().getInstrInfo();
+ if (!TII) return false;
+
+ MadeChange = false;
+
+ MF.RenumberBlocks();
+ unsigned NumBBs = MF.getNumBlockIDs();
+ BBAnalysis.resize(NumBBs);
+
+ std::vector<int> Candidates;
+ // Do an intial analysis for each basic block and finding all the potential
+ // candidates to perform if-convesion.
+ InitialFunctionAnalysis(MF, Candidates);
+
+ for (unsigned i = 0, e = Candidates.size(); i != e; ++i) {
+ BBInfo &BBI = BBAnalysis[i];
+ switch (BBI.Kind) {
+ default: assert(false && "Unexpected!");
+ break;
+ case ICTriangleEntry:
+ MadeChange |= IfConvertTriangle(BBI);
+ break;
+ case ICDiamondEntry:
+ MadeChange |= IfConvertDiamond(BBI);
+ break;
+ }
+ }
+ return MadeChange;
+}
+
+static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
+ MachineBasicBlock *TBB) {
+ for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
+ E = BB->succ_end(); SI != E; ++SI) {
+ MachineBasicBlock *SuccBB = *SI;
+ if (SuccBB != TBB)
+ return SuccBB;
+ }
+ return NULL;
+}
+
+void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
+ BBInfo &BBI = BBAnalysis[BB->getNumber()];
+
+ if (BBI.Kind != ICInvalid)
+ return; // Always analyzed.
+ BBI.EBB = BB;
+
+ // Look for 'root' of a simple (non-nested) triangle or diamond.
+ BBI.Kind = ICNotClassfied;
+ if (TII->AnalyzeBranch(*BB, BBI.TBB, BBI.FBB, BBI.Cond)
+ || !BBI.TBB || BBI.Cond.size() == 0)
+ return;
+ AnalyzeBlock(BBI.TBB);
+ BBInfo &TBBI = BBAnalysis[BBI.TBB->getNumber()];
+ if (TBBI.Kind != ICNotClassfied)
+ return;
+
+ if (!BBI.FBB)
+ BBI.FBB = findFalseBlock(BB, BBI.TBB);
+ AnalyzeBlock(BBI.FBB);
+ BBInfo &FBBI = BBAnalysis[BBI.FBB->getNumber()];
+ if (FBBI.Kind != ICNotClassfied)
+ return;
+
+ // TODO: Only handle very simple cases for now.
+ if (TBBI.FBB || FBBI.FBB || TBBI.Cond.size() > 1 || FBBI.Cond.size() > 1)
+ return;
+
+ if (TBBI.TBB && TBBI.TBB == BBI.FBB) {
+ // Triangle:
+ // EBB
+ // | \_
+ // | |
+ // | TBB
+ // | /
+ // FBB
+ BBI.Kind = ICTriangleEntry;
+ TBBI.Kind = FBBI.Kind = ICTriangle;
+ } else if (TBBI.TBB == FBBI.TBB) {
+ // Diamond:
+ // EBB
+ // / \_
+ // | |
+ // TBB FBB
+ // \ /
+ // MBB
+ // Note MBB can be empty in case both TBB and FBB are return blocks.
+ BBI.Kind = ICDiamondEntry;
+ TBBI.Kind = FBBI.Kind = ICDiamond;
+ BBI.CMBB = TBBI.TBB;
+ }
+ return;
+}
+
+void IfConverter::InitialFunctionAnalysis(MachineFunction &MF,
+ std::vector<int> &Candidates) {
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
+ MachineBasicBlock *BB = I;
+ AnalyzeBlock(BB);
+ BBInfo &BBI = BBAnalysis[BB->getNumber()];
+ if (BBI.Kind == ICTriangleEntry || BBI.Kind == ICDiamondEntry)
+ Candidates.push_back(BB->getNumber());
+ }
+}
+
+bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
+ if (isBlockPredicatable(BBI.TBB, true)) {
+ // Predicate the 'true' block after removing its branch.
+ TII->RemoveBranch(*BBI.TBB);
+ PredicateBlock(BBI.TBB, BBI.Cond);
+
+ // Join the 'true' and 'false' blocks by copying the instructions
+ // from the 'false' block to the 'true' block.
+ MergeBlocks(BBI.TBB, BBI.FBB);
+
+ // Adjust entry block, it should have but a single unconditional
+ // branch.
+ BBI.EBB->removeSuccessor(BBI.FBB);
+ TII->RemoveBranch(*BBI.EBB);
+ std::vector<MachineOperand> NoCond;
+ TII->InsertBranch(*BBI.EBB, BBI.TBB, NULL, NoCond);
+
+ // FIXME: Must maintain LiveIns.
+ NumIfConvBBs++;
+ return true;
+ }
+ return false;
+}
+
+bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
+ if (isBlockPredicatable(BBI.TBB, true) &&
+ isBlockPredicatable(BBI.FBB, true)) {
+ std::vector<MachineInstr*> Dups;
+ if (!BBI.CMBB) {
+ // No common merge block. Check if the terminators (e.g. return) are
+ // the same or predicatable.
+ MachineBasicBlock::iterator TT = BBI.TBB->getFirstTerminator();
+ MachineBasicBlock::iterator FT = BBI.FBB->getFirstTerminator();
+ while (TT != BBI.TBB->end() && FT != BBI.FBB->end()) {
+ if (TT->isIdenticalTo(FT))
+ Dups.push_back(TT); // Will erase these later.
+ else if (!TII->isPredicatable(TT) && !TII->isPredicatable(FT))
+ return false; // Can't if-convert. Abort!
+ ++TT;
+ ++FT;
+ }
+
+ while (TT != BBI.TBB->end())
+ if (!TII->isPredicatable(TT))
+ return false; // Can't if-convert. Abort!
+ while (FT != BBI.FBB->end())
+ if (!TII->isPredicatable(FT))
+ return false; // Can't if-convert. Abort!
+ }
+
+ // Remove the duplicated instructions from the 'true' block.
+ for (unsigned i = 0, e = Dups.size(); i != e; ++i)
+ Dups[i]->eraseFromParent();
+
+ // Predicate the 'true' block after removing its branch.
+ TII->RemoveBranch(*BBI.TBB);
+ PredicateBlock(BBI.TBB, BBI.Cond);
+
+ // Predicate the 'false' block.
+ std::vector<MachineOperand> NewCond(BBI.Cond);
+ TII->ReverseBranchCondition(NewCond);
+ PredicateBlock(BBI.FBB, NewCond, true);
+
+ // Join the 'true' and 'false' blocks by copying the instructions
+ // from the 'false' block to the 'true' block.
+ MergeBlocks(BBI.TBB, BBI.FBB);
+
+ // Adjust entry block, it should have but a single unconditional
+ // branch .
+ BBI.EBB->removeSuccessor(BBI.FBB);
+ TII->RemoveBranch(*BBI.EBB);
+ std::vector<MachineOperand> NoCond;
+ TII->InsertBranch(*BBI.EBB, BBI.TBB, NULL, NoCond);
+
+ // FIXME: Must maintain LiveIns.
+ NumIfConvBBs += 2;
+ return true;
+ }
+ return false;
+}
+
+/// isBlockPredicatable - Returns true if the block is predicatable. In most
+/// cases, that means all the instructions in the block has M_PREDICATED flag.
+/// If IgnoreTerm is true, assume all the terminator instructions can be
+/// converted or deleted.
+bool IfConverter::isBlockPredicatable(MachineBasicBlock *BB,
+ bool IgnoreTerm) const {
+ for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
+ I != E; ++I) {
+ if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
+ continue;
+ if (!TII->isPredicatable(I))
+ return false;
+ }
+ return true;
+}
+
+/// 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,
+ std::vector<MachineOperand> &Cond,
+ bool IgnoreTerm) {
+ for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
+ I != E; ++I) {
+ if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
+ continue;
+ TII->PredicateInstruction(&*I, Cond);
+ }
+}
+
+/// MergeBlocks - Move all instructions from FBB to the end of TBB.
+///
+void IfConverter::MergeBlocks(MachineBasicBlock *TBB, MachineBasicBlock *FBB) {
+ TBB->splice(TBB->end(), FBB, FBB->begin(), FBB->end());
+}
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