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Initial commit of (very basic) if converter.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37092 91177308-0d34-0410-b5e6-96231b3b80d8
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Evan Cheng
parent
0402e170e8
commit
4e654852f1
@ -81,6 +81,9 @@ namespace llvm {
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/// branches.
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FunctionPass *createBranchFoldingPass();
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/// IfConverter Pass - This pass performs machine code if conversion.
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FunctionPass *createIfConverterPass();
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/// DebugLabelFoldingPass - This pass prunes out redundant debug labels. This
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/// allows a debug emitter to determine if the range of two labels is empty,
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/// by seeing if the labels map to the same reduced label.
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304
lib/CodeGen/IfConversion.cpp
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304
lib/CodeGen/IfConversion.cpp
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@ -0,0 +1,304 @@
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//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the Evan Cheng and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the machine instruction level if-conversion pass.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "ifconversion"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/MachineModuleInfo.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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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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ICNotClassfied, // BB data valid, but not classified.
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ICTriangle, // BB is part of a triangle sub-CFG.
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ICDiamond, // BB is part of a diamond sub-CFG.
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ICTriangleEntry, // BB is entry of a triangle sub-CFG.
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ICDiamondEntry // BB is entry of a diamond sub-CFG.
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};
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/// BBInfo - One per MachineBasicBlock, this is used to cache the result
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/// if-conversion feasibility analysis. This includes results from
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/// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
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/// classification, and common merge block of its successors (if it's a
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/// diamond shape).
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struct BBInfo {
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BBICKind Kind;
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MachineBasicBlock *EBB;
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MachineBasicBlock *TBB;
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MachineBasicBlock *FBB;
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MachineBasicBlock *CMBB;
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std::vector<MachineOperand> Cond;
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BBInfo() : Kind(ICInvalid), EBB(0), TBB(0), FBB(0), CMBB(0) {}
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};
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/// BBAnalysis - Results of if-conversion feasibility analysis indexed by
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/// basic block number.
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std::vector<BBInfo> BBAnalysis;
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const TargetInstrInfo *TII;
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bool MadeChange;
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public:
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static char ID;
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IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
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virtual bool runOnMachineFunction(MachineFunction &MF);
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virtual const char *getPassName() const { return "If converter"; }
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private:
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void AnalyzeBlock(MachineBasicBlock *BB);
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void InitialFunctionAnalysis(MachineFunction &MF,
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std::vector<int> &Candidates);
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bool IfConvertDiamond(BBInfo &BBI);
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bool IfConvertTriangle(BBInfo &BBI);
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bool isBlockPredicatable(MachineBasicBlock *BB,
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bool IgnoreTerm = false) const;
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void PredicateBlock(MachineBasicBlock *BB,
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std::vector<MachineOperand> &Cond,
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bool IgnoreTerm = false);
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void MergeBlocks(MachineBasicBlock *TBB, MachineBasicBlock *FBB);
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};
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char IfConverter::ID = 0;
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}
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FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
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bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
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TII = MF.getTarget().getInstrInfo();
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if (!TII) return false;
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MadeChange = false;
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MF.RenumberBlocks();
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unsigned NumBBs = MF.getNumBlockIDs();
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BBAnalysis.resize(NumBBs);
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std::vector<int> 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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for (unsigned i = 0, e = Candidates.size(); i != e; ++i) {
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BBInfo &BBI = BBAnalysis[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 ICTriangleEntry:
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MadeChange |= IfConvertTriangle(BBI);
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break;
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case ICDiamondEntry:
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MadeChange |= IfConvertDiamond(BBI);
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break;
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}
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}
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return MadeChange;
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}
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static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
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MachineBasicBlock *TBB) {
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for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
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E = BB->succ_end(); SI != E; ++SI) {
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MachineBasicBlock *SuccBB = *SI;
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if (SuccBB != TBB)
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return SuccBB;
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}
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return NULL;
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}
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void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
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BBInfo &BBI = BBAnalysis[BB->getNumber()];
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if (BBI.Kind != ICInvalid)
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return; // Always analyzed.
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BBI.EBB = BB;
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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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if (TII->AnalyzeBranch(*BB, BBI.TBB, BBI.FBB, BBI.Cond)
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|| !BBI.TBB || BBI.Cond.size() == 0)
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return;
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AnalyzeBlock(BBI.TBB);
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BBInfo &TBBI = BBAnalysis[BBI.TBB->getNumber()];
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if (TBBI.Kind != ICNotClassfied)
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return;
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if (!BBI.FBB)
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BBI.FBB = findFalseBlock(BB, BBI.TBB);
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AnalyzeBlock(BBI.FBB);
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BBInfo &FBBI = BBAnalysis[BBI.FBB->getNumber()];
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if (FBBI.Kind != ICNotClassfied)
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return;
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// TODO: Only handle very simple cases for now.
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if (TBBI.FBB || FBBI.FBB || TBBI.Cond.size() > 1 || FBBI.Cond.size() > 1)
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return;
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if (TBBI.TBB && TBBI.TBB == BBI.FBB) {
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// Triangle:
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// EBB
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// | \_
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// | |
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// | TBB
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// | /
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// FBB
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BBI.Kind = ICTriangleEntry;
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TBBI.Kind = FBBI.Kind = ICTriangle;
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} else if (TBBI.TBB == FBBI.TBB) {
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// Diamond:
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// EBB
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// / \_
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// | |
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// TBB FBB
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// \ /
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// MBB
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// Note MBB can be empty in case both TBB and FBB are return blocks.
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BBI.Kind = ICDiamondEntry;
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TBBI.Kind = FBBI.Kind = ICDiamond;
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BBI.CMBB = TBBI.TBB;
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}
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return;
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}
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void IfConverter::InitialFunctionAnalysis(MachineFunction &MF,
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std::vector<int> &Candidates) {
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for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
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MachineBasicBlock *BB = I;
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AnalyzeBlock(BB);
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BBInfo &BBI = BBAnalysis[BB->getNumber()];
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if (BBI.Kind == ICTriangleEntry || BBI.Kind == ICDiamondEntry)
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Candidates.push_back(BB->getNumber());
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}
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}
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bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
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if (isBlockPredicatable(BBI.TBB, true)) {
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// Predicate the 'true' block after removing its branch.
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TII->RemoveBranch(*BBI.TBB);
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PredicateBlock(BBI.TBB, BBI.Cond);
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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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MergeBlocks(BBI.TBB, BBI.FBB);
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// Adjust entry block, it should have but a single unconditional
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// branch.
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BBI.EBB->removeSuccessor(BBI.FBB);
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TII->RemoveBranch(*BBI.EBB);
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std::vector<MachineOperand> NoCond;
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TII->InsertBranch(*BBI.EBB, BBI.TBB, NULL, NoCond);
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// FIXME: Must maintain LiveIns.
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NumIfConvBBs++;
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return true;
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}
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return false;
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}
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bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
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if (isBlockPredicatable(BBI.TBB, true) &&
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isBlockPredicatable(BBI.FBB, true)) {
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std::vector<MachineInstr*> Dups;
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if (!BBI.CMBB) {
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// No common merge block. Check if the terminators (e.g. return) are
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// the same or predicatable.
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MachineBasicBlock::iterator TT = BBI.TBB->getFirstTerminator();
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MachineBasicBlock::iterator FT = BBI.FBB->getFirstTerminator();
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while (TT != BBI.TBB->end() && FT != BBI.FBB->end()) {
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if (TT->isIdenticalTo(FT))
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Dups.push_back(TT); // Will erase these later.
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else if (!TII->isPredicatable(TT) && !TII->isPredicatable(FT))
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return false; // Can't if-convert. Abort!
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++TT;
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++FT;
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}
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while (TT != BBI.TBB->end())
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if (!TII->isPredicatable(TT))
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return false; // Can't if-convert. Abort!
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while (FT != BBI.FBB->end())
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if (!TII->isPredicatable(FT))
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return false; // Can't if-convert. Abort!
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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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// Predicate the 'true' block after removing its branch.
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TII->RemoveBranch(*BBI.TBB);
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PredicateBlock(BBI.TBB, BBI.Cond);
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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.FBB, NewCond, true);
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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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MergeBlocks(BBI.TBB, BBI.FBB);
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// Adjust entry block, it should have but a single unconditional
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// branch .
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BBI.EBB->removeSuccessor(BBI.FBB);
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TII->RemoveBranch(*BBI.EBB);
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std::vector<MachineOperand> NoCond;
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TII->InsertBranch(*BBI.EBB, BBI.TBB, NULL, NoCond);
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// FIXME: Must maintain LiveIns.
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NumIfConvBBs += 2;
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return true;
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}
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return false;
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}
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/// isBlockPredicatable - Returns true if the block is predicatable. In most
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/// cases, that means all the instructions in the block has M_PREDICATED flag.
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/// If IgnoreTerm is true, assume all the terminator instructions can be
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/// converted or deleted.
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bool IfConverter::isBlockPredicatable(MachineBasicBlock *BB,
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bool IgnoreTerm) const {
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for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
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I != E; ++I) {
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if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
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continue;
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if (!TII->isPredicatable(I))
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return false;
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}
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return true;
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}
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/// PredicateBlock - Predicate every instruction in the block with the specified
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/// condition. If IgnoreTerm is true, skip over all terminator instructions.
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void IfConverter::PredicateBlock(MachineBasicBlock *BB,
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std::vector<MachineOperand> &Cond,
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bool IgnoreTerm) {
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for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
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I != E; ++I) {
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if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
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continue;
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TII->PredicateInstruction(&*I, Cond);
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}
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}
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/// MergeBlocks - Move all instructions from FBB to the end of TBB.
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///
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void IfConverter::MergeBlocks(MachineBasicBlock *TBB, MachineBasicBlock *FBB) {
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TBB->splice(TBB->end(), FBB, FBB->begin(), FBB->end());
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}
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