[llvm-commits] [llvm] r114981 - /llvm/trunk/lib/CodeGen/IfConversion.cpp
Owen Anderson
resistor at mac.com
Tue Sep 28 13:42:15 PDT 2010
Author: resistor
Date: Tue Sep 28 15:42:15 2010
New Revision: 114981
URL: http://llvm.org/viewvc/llvm-project?rev=114981&view=rev
Log:
Give the if-converter access to MachineLoopInfo, and use it to generate plausible branch prediction
estimates.
Modified:
llvm/trunk/lib/CodeGen/IfConversion.cpp
Modified: llvm/trunk/lib/CodeGen/IfConversion.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/IfConversion.cpp?rev=114981&r1=114980&r2=114981&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/IfConversion.cpp (original)
+++ llvm/trunk/lib/CodeGen/IfConversion.cpp Tue Sep 28 15:42:15 2010
@@ -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 @@
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 @@
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 @@
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 @@
/// 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 @@
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 @@
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 @@
}
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 @@
}
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 @@
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;
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