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Give the if-converter access to MachineLoopInfo, and use it to generate plausible branch prediction

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estimates.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114981 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2010-09-28 20:42:15 +00:00
parent b0db4d0ee7
commit 7571ee7885
1 changed files with 50 additions and 16 deletions
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66
lib/CodeGen/IfConversion.cpp
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@ -17,6 +17,7 @@
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetInstrItineraries.h"
#include "llvm/Target/TargetLowering.h"
@ -152,18 +153,24 @@ namespace {
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
const InstrItineraryData *InstrItins;
const MachineLoopInfo *MLI;
bool MadeChange;
int FnNum;
public:
static char ID;
IfConverter() : MachineFunctionPass(ID), FnNum(-1) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<MachineLoopInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const { return "If Converter"; }
private:
bool ReverseBranchCondition(BBInfo &BBI);
bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups, float Prediction) const;
bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch, unsigned &Dups) const;
bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
@ -190,14 +197,16 @@ namespace {
bool IgnoreBr = false);
void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true);
bool MeetIfcvtSizeLimit(MachineBasicBlock &BB, unsigned Size) const {
return Size > 0 && TII->isProfitableToIfCvt(BB, Size, 0.5);
bool MeetIfcvtSizeLimit(MachineBasicBlock &BB, unsigned Size,
float Prediction) const {
return Size > 0 && TII->isProfitableToIfCvt(BB, Size, Prediction);
}
bool MeetIfcvtSizeLimit(MachineBasicBlock &TBB, unsigned TSize,
MachineBasicBlock &FBB, unsigned FSize) const {
MachineBasicBlock &FBB, unsigned FSize,
float Prediction) const {
return TSize > 0 && FSize > 0 &&
TII->isProfitableToIfCvt(TBB, TSize, FBB, FSize, 0.5);
TII->isProfitableToIfCvt(TBB, TSize, FBB, FSize, Prediction);
}
// blockAlwaysFallThrough - Block ends without a terminator.
@ -240,6 +249,7 @@ bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
TLI = MF.getTarget().getTargetLowering();
TII = MF.getTarget().getInstrInfo();
TRI = MF.getTarget().getRegisterInfo();
MLI = &getAnalysis<MachineLoopInfo>();
InstrItins = MF.getTarget().getInstrItineraryData();
if (!TII) return false;
@ -434,7 +444,8 @@ static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
/// predecessor) forms a valid simple shape for ifcvt. It also returns the
/// number of instructions that the ifcvt would need to duplicate if performed
/// in Dups.
bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
float Prediction) const {
Dups = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
return false;
@ -444,7 +455,8 @@ bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
if (TrueBBI.BB->pred_size() > 1) {
if (TrueBBI.CannotBeCopied ||
!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize, 0.5))
!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize,
Prediction))
return false;
Dups = TrueBBI.NonPredSize;
}
@ -769,9 +781,31 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
bool TNeedSub = TrueBBI.Predicate.size() > 0;
bool FNeedSub = FalseBBI.Predicate.size() > 0;
bool Enqueued = false;
// Try to predict the branch, using loop info to guide us.
// General heuristics are:
// - backedge -> 90% taken
// - early exit -> 20% taken
float Prediction = 0.5;
MachineLoop *Loop = MLI->getLoopFor(BB);
if (Loop) {
if (TrueBBI.BB == Loop->getHeader())
Prediction = 0.9;
else if (FalseBBI.BB == Loop->getHeader())
Prediction = 0.1;
MachineLoop *TrueLoop = MLI->getLoopFor(TrueBBI.BB);
MachineLoop *FalseLoop = MLI->getLoopFor(FalseBBI.BB);
if (!TrueLoop || TrueLoop->getParentLoop() == Loop)
Prediction = 0.2;
else if (!FalseLoop || FalseLoop->getParentLoop() == Loop)
Prediction = 0.8;
}
if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize - (Dups + Dups2),
*FalseBBI.BB, FalseBBI.NonPredSize - (Dups + Dups2)) &&
*FalseBBI.BB, FalseBBI.NonPredSize - (Dups + Dups2),
Prediction) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
@ -788,7 +822,7 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
}
if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize, Prediction) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
// Triangle:
// EBB
@ -802,14 +836,14 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
}
if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize, Prediction) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
Enqueued = true;
}
if (ValidSimple(TrueBBI, Dups) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize) &&
if (ValidSimple(TrueBBI, Dups, Prediction) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize, Prediction) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
// Simple (split, no rejoin):
// EBB
@ -825,21 +859,21 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
if (CanRevCond) {
// Try the other path...
if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize,1.0-Prediction) &&
FeasibilityAnalysis(FalseBBI, RevCond, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
Enqueued = true;
}
if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize,1.0-Prediction) &&
FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
Enqueued = true;
}
if (ValidSimple(FalseBBI, Dups) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize) &&
if (ValidSimple(FalseBBI, Dups, 1.0-Prediction) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize,1.0-Prediction) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
Enqueued = true;