Initial commit of (very basic) if converter.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37092 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2007-05-16 02:00:57 +00:00
parent 0402e170e8
commit 4e654852f1
2 changed files with 307 additions and 0 deletions

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@ -81,6 +81,9 @@ namespace llvm {
/// branches.
FunctionPass *createBranchFoldingPass();
/// IfConverter Pass - This pass performs machine code if conversion.
FunctionPass *createIfConverterPass();
/// DebugLabelFoldingPass - This pass prunes out redundant debug labels. This
/// allows a debug emitter to determine if the range of two labels is empty,
/// by seeing if the labels map to the same reduced label.

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@ -0,0 +1,304 @@
//===-- 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());
}