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https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37231 91177308-0d34-0410-b5e6-96231b3b80d8
448 lines
15 KiB
C++
448 lines
15 KiB
C++
//===-- 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/TargetLowering.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 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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struct BBInfo {
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BBICKind Kind;
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unsigned Size;
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bool isPredicable;
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bool ClobbersPred;
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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), BB(0), TrueBB(0), FalseBB(0), TailBB(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 TargetLowering *TLI;
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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 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<int> &Candidates);
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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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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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};
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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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TLI = MF.getTarget().getTargetLowering();
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TII = MF.getTarget().getInstrInfo();
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if (!TII) return 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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MadeChange = false;
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for (unsigned i = 0, e = Candidates.size(); i != e; ++i) {
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BBInfo &BBI = BBAnalysis[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 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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BBAnalysis.clear();
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return MadeChange;
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}
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static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
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MachineBasicBlock *TrueBB) {
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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 != TrueBB)
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return SuccBB;
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}
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return NULL;
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}
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/// StructuralAnalysis - Analyze the structure of the sub-CFG starting from
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/// the specified block. Record its successors and whether it looks like an
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/// if-conversion candidate.
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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; // Always analyzed.
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BBI.BB = BB;
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BBI.Size = 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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if (TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB, BBI.Cond)
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|| !BBI.TrueBB || BBI.Cond.size() == 0)
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return;
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// Not a candidate if 'true' block has another predecessor.
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// FIXME: Use or'd predicate or predicated cmp.
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if (BBI.TrueBB->pred_size() > 1)
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return;
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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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BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
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if (TrueBBI.Kind != ICNotClassfied)
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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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return;
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// No false branch. This BB must end with a conditional branch and a
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// fallthrough.
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if (!BBI.FalseBB)
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BBI.FalseBB = findFalseBlock(BB, BBI.TrueBB);
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assert(BBI.FalseBB && "Expected to find the fallthrough block!");
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// Not a candidate if 'false' block has another predecessor.
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// FIXME: Invert condition and swap 'true' / 'false' blocks?
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if (BBI.FalseBB->pred_size() > 1)
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return;
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// Not a candidate if 'false' block is going to be if-converted.
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StructuralAnalysis(BBI.FalseBB);
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BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
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if (FalseBBI.Kind != ICNotClassfied)
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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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return;
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if (TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB) {
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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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TrueBBI.Kind = FalseBBI.Kind = ICTriangle;
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} else if (TrueBBI.TrueBB == FalseBBI.TrueBB) {
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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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// TailBB
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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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TrueBBI.Kind = FalseBBI.Kind = ICDiamond;
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BBI.TailBB = TrueBBI.TrueBB;
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}
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return;
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}
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/// FeasibilityAnalysis - Determine if the block is predicable. In most
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/// cases, that means all the instructions in the block has M_PREDICABLE flag.
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/// Also checks if the block contains any instruction which can clobber a
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/// predicate (e.g. condition code register). If so, the block is not
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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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return;
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for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
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I != E; ++I) {
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// TODO: check if instruction clobbers predicate.
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if (TII->isTerminatorInstr(I->getOpcode()))
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break;
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if (!I->isPredicable())
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return;
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}
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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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/// if-conversion candidates.
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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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StructuralAnalysis(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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/// TransferPreds - Transfer all the predecessors of FromBB to ToBB.
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///
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static void TransferPreds(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
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std::vector<MachineBasicBlock*> Preds(FromBB->pred_begin(),
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FromBB->pred_end());
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for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
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MachineBasicBlock *Pred = Preds[i];
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Pred->removeSuccessor(FromBB);
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if (!Pred->isSuccessor(ToBB))
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Pred->addSuccessor(ToBB);
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}
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}
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/// TransferSuccs - Transfer all the successors of FromBB to ToBB.
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///
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static void TransferSuccs(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
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std::vector<MachineBasicBlock*> Succs(FromBB->succ_begin(),
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FromBB->succ_end());
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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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FromBB->removeSuccessor(Succ);
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if (!ToBB->isSuccessor(Succ))
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ToBB->addSuccessor(Succ);
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}
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}
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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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if (TrueBBI.isPredicable) {
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BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
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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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// 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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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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MergeBlocks(BBI, TrueBBI);
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// Update block info.
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TrueBBI.Kind = ICInvalid;
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FalseBBI.Kind = ICInvalid;
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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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/// IfConvertDiamond - If convert a diamond sub-CFG.
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///
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bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
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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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if (TrueBBI.isPredicable && FalseBBI.isPredicable) {
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// Check the 'true' and 'false' blocks if either isn't ended with a branch.
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// Either the block fallthrough to another block or it ends with a
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// return. If it's the former, add a conditional branch to its successor.
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bool Proceed = true;
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bool TrueNeedCBr = !TrueBBI.TrueBB && BBI.TrueBB->succ_size();
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bool FalseNeedCBr = !FalseBBI.TrueBB && BBI.FalseBB->succ_size();
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if (TrueNeedCBr && TrueBBI.ClobbersPred) {
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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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FalseBBI.isPredicable = false;
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Proceed = false;
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}
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if (!Proceed)
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return false;
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std::vector<MachineInstr*> Dups;
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if (!BBI.TailBB) {
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// No common merge block. Check if the terminators (e.g. return) are
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// the same or predicable.
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MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
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MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
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while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->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 (!TT->isPredicable() && !FT->isPredicable())
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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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// One of the two pathes have more terminators, make sure they are all
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// predicable.
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while (TT != BBI.TrueBB->end())
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if (!TT->isPredicable())
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return false; // Can't if-convert. Abort!
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while (FT != BBI.FalseBB->end())
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if (!FT->isPredicable())
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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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--TrueBBI.Size;
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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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// Add a conditional branch to 'true' successor if needed.
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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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// 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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// Add a conditional branch to 'false' successor if needed.
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if (FalseNeedCBr)
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TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,NewCond);
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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.
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MergeBlocks(TrueBBI, FalseBBI);
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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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// Merge the combined block into the entry of the diamond if the entry
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// block is the only predecessor. Otherwise, insert an unconditional
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// branch.
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BBInfo *CvtBBI = &TrueBBI;
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if (BBI.TrueBB->pred_size() == 1) {
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BBI.BB->removeSuccessor(BBI.TrueBB);
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MergeBlocks(BBI, TrueBBI);
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CvtBBI = &BBI;
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} else {
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std::vector<MachineOperand> NoCond;
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TII->InsertBranch(*BBI.BB, BBI.TrueBB, NULL, NoCond);
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}
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// If the if-converted block fallthrough into the tail block, then
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// fold the tail block in as well.
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if (BBI.TailBB && CvtBBI->BB->succ_size() == 1) {
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CvtBBI->Size -= TII->RemoveBranch(*CvtBBI->BB);
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CvtBBI->BB->removeSuccessor(BBI.TailBB);
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BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
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MergeBlocks(*CvtBBI, TailBBI);
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TailBBI.Kind = ICInvalid;
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}
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// Update block info.
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TrueBBI.Kind = ICInvalid;
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FalseBBI.Kind = ICInvalid;
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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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/// 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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if (!TII->PredicateInstruction(&*I, Cond)) {
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cerr << "Unable to predication " << *I << "!\n";
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abort();
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}
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}
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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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ToBBI.BB->splice(ToBBI.BB->end(),
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FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
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TransferPreds(ToBBI.BB, FromBBI.BB);
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TransferSuccs(ToBBI.BB, FromBBI.BB);
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ToBBI.Size += FromBBI.Size;
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FromBBI.Size = 0;
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}
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