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Thread the determination of branch prediction hit rates back through the if-conversion heuristic APIs. For now,

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stick with a constant estimate of 90% (branch predictors are good!), but we might find that we want to provide
more nuanced estimates in the future.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115364 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson
2010-10-01 22:45:50 +00:00
parent 6314ef9e81
commit e3cc84a43d
6 changed files with 67 additions and 42 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/CodeGen/IfConversion.cpp
+39 -23
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@@ -170,9 +170,11 @@ namespace {
private:
bool ReverseBranchCondition(BBInfo &BBI);
bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups, float Prediction) 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);
@@ -198,15 +200,17 @@ namespace {
void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true);
bool MeetIfcvtSizeLimit(MachineBasicBlock &BB, unsigned Size,
float Prediction) const {
return Size > 0 && TII->isProfitableToIfCvt(BB, Size, Prediction);
float Prediction, float Confidence) const {
return Size > 0 && TII->isProfitableToIfCvt(BB, Size,
Prediction, Confidence);
}
bool MeetIfcvtSizeLimit(MachineBasicBlock &TBB, unsigned TSize,
MachineBasicBlock &FBB, unsigned FSize,
float Prediction) const {
float Prediction, float Confidence) const {
return TSize > 0 && FSize > 0 &&
TII->isProfitableToIfCvt(TBB, TSize, FBB, FSize, Prediction);
TII->isProfitableToIfCvt(TBB, TSize, FBB, FSize,
Prediction, Confidence);
}
// blockAlwaysFallThrough - Block ends without a terminator.
@@ -445,7 +449,7 @@ static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
/// number of instructions that the ifcvt would need to duplicate if performed
/// in Dups.
bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
float Prediction) const {
float Prediction, float Confidence) const {
Dups = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
return false;
@@ -456,7 +460,7 @@ bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
if (TrueBBI.BB->pred_size() > 1) {
if (TrueBBI.CannotBeCopied ||
!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize,
Prediction))
Prediction, Confidence))
return false;
Dups = TrueBBI.NonPredSize;
}
@@ -471,7 +475,8 @@ bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
/// 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;
@@ -493,7 +498,8 @@ bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
++Size;
}
}
if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size, 0.5))
if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size,
Prediction, Confidence))
return false;
Dups = Size;
}
@@ -786,7 +792,9 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
// 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())
@@ -805,7 +813,7 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize - (Dups + Dups2),
*FalseBBI.BB, FalseBBI.NonPredSize - (Dups + Dups2),
Prediction) &&
Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
@@ -821,8 +829,9 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
Enqueued = true;
}
if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize, Prediction) &&
if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction, Confidence) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize,
Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
// Triangle:
// EBB
@@ -835,15 +844,17 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
Enqueued = true;
}
if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize, Prediction) &&
if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction, Confidence) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize,
Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
Enqueued = true;
}
if (ValidSimple(TrueBBI, Dups, Prediction) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize, Prediction) &&
if (ValidSimple(TrueBBI, Dups, Prediction, Confidence) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize,
Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
// Simple (split, no rejoin):
// EBB
@@ -858,22 +869,27 @@ IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
if (CanRevCond) {
// Try the other path...
if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize,1.0-Prediction) &&
if (ValidTriangle(FalseBBI, TrueBBI, false, Dups,
1.0-Prediction, Confidence) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize,
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,1.0-Prediction) &&
if (ValidTriangle(FalseBBI, TrueBBI, true, Dups,
1.0-Prediction, Confidence) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize,
1.0-Prediction, Confidence) &&
FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
Enqueued = true;
}
if (ValidSimple(FalseBBI, Dups, 1.0-Prediction) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize,1.0-Prediction) &&
if (ValidSimple(FalseBBI, Dups, 1.0-Prediction, Confidence) &&
MeetIfcvtSizeLimit(*FalseBBI.BB, FalseBBI.NonPredSize,
1.0-Prediction, Confidence) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
Enqueued = true;