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-rw-r--r--lib/CodeGen/IfConversion.cpp247
1 files changed, 164 insertions, 83 deletions
diff --git a/lib/CodeGen/IfConversion.cpp b/lib/CodeGen/IfConversion.cpp
index 0ea30d7a7929..db53b0473a9a 100644
--- a/lib/CodeGen/IfConversion.cpp
+++ b/lib/CodeGen/IfConversion.cpp
@@ -17,7 +17,9 @@
#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"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
@@ -26,6 +28,7 @@
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
@@ -91,6 +94,8 @@ namespace {
/// ClobbersPred - True if BB could modify predicates (e.g. has
/// cmp, call, etc.)
/// NonPredSize - Number of non-predicated instructions.
+ /// ExtraCost - Extra cost for multi-cycle instructions.
+ /// ExtraCost2 - Some instructions are slower when predicated
/// BB - Corresponding MachineBasicBlock.
/// TrueBB / FalseBB- See AnalyzeBranch().
/// BrCond - Conditions for end of block conditional branches.
@@ -106,6 +111,8 @@ namespace {
bool CannotBeCopied : 1;
bool ClobbersPred : 1;
unsigned NonPredSize;
+ unsigned ExtraCost;
+ unsigned ExtraCost2;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
MachineBasicBlock *FalseBB;
@@ -115,7 +122,7 @@ namespace {
IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
HasFallThrough(false), IsUnpredicable(false),
CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
- BB(0), TrueBB(0), FalseBB(0) {}
+ ExtraCost(0), ExtraCost2(0), BB(0), TrueBB(0), FalseBB(0) {}
};
/// IfcvtToken - Record information about pending if-conversions to attempt:
@@ -150,20 +157,31 @@ namespace {
const TargetLowering *TLI;
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) {}
+ IfConverter() : MachineFunctionPass(ID), FnNum(-1) {
+ initializeIfConverterPass(*PassRegistry::getPassRegistry());
+ }
+
+ 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, float Confidence) const;
bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
- bool FalseBranch, unsigned &Dups) const;
+ bool FalseBranch, unsigned &Dups,
+ float Prediction, float Confidence) const;
bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
unsigned &Dups1, unsigned &Dups2) const;
void ScanInstructions(BBInfo &BBI);
@@ -188,14 +206,21 @@ 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);
+ bool MeetIfcvtSizeLimit(MachineBasicBlock &BB,
+ unsigned Cycle, unsigned Extra,
+ float Prediction, float Confidence) const {
+ return Cycle > 0 && TII->isProfitableToIfCvt(BB, Cycle, Extra,
+ Prediction, Confidence);
}
- bool MeetIfcvtSizeLimit(MachineBasicBlock &TBB, unsigned TSize,
- MachineBasicBlock &FBB, unsigned FSize) const {
- return TSize > 0 && FSize > 0 &&
- TII->isProfitableToIfCvt(TBB, TSize, FBB, FSize);
+ bool MeetIfcvtSizeLimit(MachineBasicBlock &TBB,
+ unsigned TCycle, unsigned TExtra,
+ MachineBasicBlock &FBB,
+ unsigned FCycle, unsigned FExtra,
+ float Prediction, float Confidence) const {
+ return TCycle > 0 && FCycle > 0 &&
+ TII->isProfitableToIfCvt(TBB, TCycle, TExtra, FBB, FCycle, FExtra,
+ Prediction, Confidence);
}
// blockAlwaysFallThrough - Block ends without a terminator.
@@ -230,7 +255,9 @@ namespace {
char IfConverter::ID = 0;
}
-INITIALIZE_PASS(IfConverter, "if-converter", "If Converter", false, false);
+INITIALIZE_PASS_BEGIN(IfConverter, "if-converter", "If Converter", false, false)
+INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
+INITIALIZE_PASS_END(IfConverter, "if-converter", "If Converter", false, false)
FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
@@ -238,6 +265,8 @@ 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;
// Tail merge tend to expose more if-conversion opportunities.
@@ -431,7 +460,8 @@ 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, float Confidence) const {
Dups = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
return false;
@@ -441,7 +471,8 @@ bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
if (TrueBBI.BB->pred_size() > 1) {
if (TrueBBI.CannotBeCopied ||
- !TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize))
+ !TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize,
+ Prediction, Confidence))
return false;
Dups = TrueBBI.NonPredSize;
}
@@ -456,7 +487,8 @@ bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
/// returns the number of instructions that the ifcvt would need to duplicate
/// if performed in 'Dups'.
bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
- bool FalseBranch, unsigned &Dups) const {
+ bool FalseBranch, unsigned &Dups,
+ float Prediction, float Confidence) const {
Dups = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
return false;
@@ -478,7 +510,8 @@ bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
++Size;
}
}
- if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size))
+ if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size,
+ Prediction, Confidence))
return false;
Dups = Size;
}
@@ -493,18 +526,6 @@ bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
return TExit && TExit == FalseBBI.BB;
}
-static
-MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
- const TargetInstrInfo *TII) {
- MachineBasicBlock::iterator I = BB->end();
- while (I != BB->begin()) {
- --I;
- if (!I->getDesc().isBranch())
- break;
- }
- return I;
-}
-
/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid diamond shape for ifcvt.
bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
@@ -533,64 +554,70 @@ bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
(TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
return false;
- MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
- MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
+ // Count duplicate instructions at the beginning of the true and false blocks.
+ MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
+ MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
MachineBasicBlock::iterator TIE = TrueBBI.BB->end();
MachineBasicBlock::iterator FIE = FalseBBI.BB->end();
- // Skip dbg_value instructions
- while (TI != TIE && TI->isDebugValue())
- ++TI;
- while (FI != FIE && FI->isDebugValue())
- ++FI;
- while (TI != TIE && FI != FIE) {
+ while (TIB != TIE && FIB != FIE) {
// Skip dbg_value instructions. These do not count.
- if (TI->isDebugValue()) {
- while (TI != TIE && TI->isDebugValue())
- ++TI;
- if (TI == TIE)
+ if (TIB->isDebugValue()) {
+ while (TIB != TIE && TIB->isDebugValue())
+ ++TIB;
+ if (TIB == TIE)
break;
}
- if (FI->isDebugValue()) {
- while (FI != FIE && FI->isDebugValue())
- ++FI;
- if (FI == FIE)
+ if (FIB->isDebugValue()) {
+ while (FIB != FIE && FIB->isDebugValue())
+ ++FIB;
+ if (FIB == FIE)
break;
}
- if (!TI->isIdenticalTo(FI))
+ if (!TIB->isIdenticalTo(FIB))
break;
++Dups1;
- ++TI;
- ++FI;
+ ++TIB;
+ ++FIB;
}
- TI = firstNonBranchInst(TrueBBI.BB, TII);
- FI = firstNonBranchInst(FalseBBI.BB, TII);
- MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
- MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
- // Skip dbg_value instructions at end of the bb's.
- while (TI != TIB && TI->isDebugValue())
- --TI;
- while (FI != FIB && FI->isDebugValue())
- --FI;
- while (TI != TIB && FI != FIB) {
+ // Now, in preparation for counting duplicate instructions at the ends of the
+ // blocks, move the end iterators up past any branch instructions.
+ while (TIE != TIB) {
+ --TIE;
+ if (!TIE->getDesc().isBranch())
+ break;
+ }
+ while (FIE != FIB) {
+ --FIE;
+ if (!FIE->getDesc().isBranch())
+ break;
+ }
+
+ // If Dups1 includes all of a block, then don't count duplicate
+ // instructions at the end of the blocks.
+ if (TIB == TIE || FIB == FIE)
+ return true;
+
+ // Count duplicate instructions at the ends of the blocks.
+ while (TIE != TIB && FIE != FIB) {
// Skip dbg_value instructions. These do not count.
- if (TI->isDebugValue()) {
- while (TI != TIB && TI->isDebugValue())
- --TI;
- if (TI == TIB)
+ if (TIE->isDebugValue()) {
+ while (TIE != TIB && TIE->isDebugValue())
+ --TIE;
+ if (TIE == TIB)
break;
}
- if (FI->isDebugValue()) {
- while (FI != FIB && FI->isDebugValue())
- --FI;
- if (FI == FIB)
+ if (FIE->isDebugValue()) {
+ while (FIE != FIB && FIE->isDebugValue())
+ --FIE;
+ if (FIE == FIB)
break;
}
- if (!TI->isIdenticalTo(FI))
+ if (!TIE->isIdenticalTo(FIE))
break;
++Dups2;
- --TI;
- --FI;
+ --TIE;
+ --FIE;
}
return true;
@@ -627,6 +654,8 @@ void IfConverter::ScanInstructions(BBInfo &BBI) {
// Then scan all the instructions.
BBI.NonPredSize = 0;
+ BBI.ExtraCost = 0;
+ BBI.ExtraCost2 = 0;
BBI.ClobbersPred = false;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
@@ -641,9 +670,15 @@ void IfConverter::ScanInstructions(BBInfo &BBI) {
bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
if (!isCondBr) {
- if (!isPredicated)
+ if (!isPredicated) {
BBI.NonPredSize++;
- else if (!AlreadyPredicated) {
+ unsigned ExtraPredCost = 0;
+ unsigned NumCycles = TII->getInstrLatency(InstrItins, &*I,
+ &ExtraPredCost);
+ if (NumCycles > 1)
+ BBI.ExtraCost += NumCycles-1;
+ BBI.ExtraCost2 += ExtraPredCost;
+ } else if (!AlreadyPredicated) {
// FIXME: This instruction is already predicated before the
// if-conversion pass. It's probably something like a conditional move.
// Mark this block unpredicable for now.
@@ -765,9 +800,35 @@ 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
+ // - branch predictor confidence -> 90%
+ float Prediction = 0.5f;
+ float Confidence = 0.9f;
+ MachineLoop *Loop = MLI->getLoopFor(BB);
+ if (Loop) {
+ if (TrueBBI.BB == Loop->getHeader())
+ Prediction = 0.9f;
+ else if (FalseBBI.BB == Loop->getHeader())
+ Prediction = 0.1f;
+
+ MachineLoop *TrueLoop = MLI->getLoopFor(TrueBBI.BB);
+ MachineLoop *FalseLoop = MLI->getLoopFor(FalseBBI.BB);
+ if (!TrueLoop || TrueLoop->getParentLoop() == Loop)
+ Prediction = 0.2f;
+ else if (!FalseLoop || FalseLoop->getParentLoop() == Loop)
+ Prediction = 0.8f;
+ }
+
if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
- MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize - (Dups + Dups2),
- *FalseBBI.BB, FalseBBI.NonPredSize - (Dups + Dups2)) &&
+ MeetIfcvtSizeLimit(*TrueBBI.BB, (TrueBBI.NonPredSize - (Dups + Dups2) +
+ TrueBBI.ExtraCost), TrueBBI.ExtraCost2,
+ *FalseBBI.BB, (FalseBBI.NonPredSize - (Dups + Dups2) +
+ FalseBBI.ExtraCost),FalseBBI.ExtraCost2,
+ Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
@@ -783,8 +844,9 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
Enqueued = true;
}
- if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
- MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize) &&
+ if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction, Confidence) &&
+ MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
+ TrueBBI.ExtraCost2, Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
// Triangle:
// EBB
@@ -797,15 +859,17 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
Enqueued = true;
}
- if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
- MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize) &&
+ if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction, Confidence) &&
+ MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
+ TrueBBI.ExtraCost2, Prediction, Confidence) &&
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, Confidence) &&
+ MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
+ TrueBBI.ExtraCost2, Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
// Simple (split, no rejoin):
// EBB
@@ -820,22 +884,30 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
if (CanRevCond) {
// Try the other path...
- if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
- MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize) &&
+ if (ValidTriangle(FalseBBI, TrueBBI, false, Dups,
+ 1.0-Prediction, Confidence) &&
+ MeetIfcvtSizeLimit(*FalseBBI.BB,
+ FalseBBI.NonPredSize + FalseBBI.ExtraCost,
+ FalseBBI.ExtraCost2, 1.0-Prediction, Confidence) &&
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) &&
+ if (ValidTriangle(FalseBBI, TrueBBI, true, Dups,
+ 1.0-Prediction, Confidence) &&
+ MeetIfcvtSizeLimit(*FalseBBI.BB,
+ FalseBBI.NonPredSize + FalseBBI.ExtraCost,
+ FalseBBI.ExtraCost2, 1.0-Prediction, Confidence) &&
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, Confidence) &&
+ MeetIfcvtSizeLimit(*FalseBBI.BB,
+ FalseBBI.NonPredSize + FalseBBI.ExtraCost,
+ FalseBBI.ExtraCost2, 1.0-Prediction, Confidence) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
Enqueued = true;
@@ -1365,6 +1437,11 @@ void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
MachineInstr *MI = MF.CloneMachineInstr(I);
ToBBI.BB->insert(ToBBI.BB->end(), MI);
ToBBI.NonPredSize++;
+ unsigned ExtraPredCost = 0;
+ unsigned NumCycles = TII->getInstrLatency(InstrItins, &*I, &ExtraPredCost);
+ if (NumCycles > 1)
+ ToBBI.ExtraCost += NumCycles-1;
+ ToBBI.ExtraCost2 += ExtraPredCost;
if (!TII->isPredicated(I) && !MI->isDebugValue()) {
if (!TII->PredicateInstruction(MI, Cond)) {
@@ -1438,7 +1515,11 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) {
FromBBI.Predicate.clear();
ToBBI.NonPredSize += FromBBI.NonPredSize;
+ ToBBI.ExtraCost += FromBBI.ExtraCost;
+ ToBBI.ExtraCost2 += FromBBI.ExtraCost2;
FromBBI.NonPredSize = 0;
+ FromBBI.ExtraCost = 0;
+ FromBBI.ExtraCost2 = 0;
ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
ToBBI.HasFallThrough = FromBBI.HasFallThrough;
generated by cgit v1.2.3 (git 2.25.1) at 2024-10-27 01:49:19 +0000