[llvm] r279167 - IfConversion: Rescan diamonds.
Kyle Butt via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 18 15:09:25 PDT 2016
Author: iteratee
Date: Thu Aug 18 17:09:25 2016
New Revision: 279167
URL: http://llvm.org/viewvc/llvm-project?rev=279167&view=rev
Log:
IfConversion: Rescan diamonds.
The cost of predicating a diamond is only the instructions that are not shared
between the two branches. Additionally If a predicate clobbering instruction
occurs in the shared portion of the branches (e.g. a cond move), it may still
be possible to if convert the sub-cfg. This change handles these two facts by
rescanning the non-shared portion of a diamond sub-cfg to recalculate both the
predication cost and whether both blocks are pred-clobbering.
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=279167&r1=279166&r2=279167&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/IfConversion.cpp (original)
+++ llvm/trunk/lib/CodeGen/IfConversion.cpp Thu Aug 18 17:09:25 2016
@@ -149,11 +149,15 @@ namespace {
struct IfcvtToken {
BBInfo &BBI;
IfcvtKind Kind;
- bool NeedSubsumption;
unsigned NumDups;
unsigned NumDups2;
- IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
- : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
+ bool NeedSubsumption : 1;
+ bool TClobbersPred : 1;
+ bool FClobbersPred : 1;
+ IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0,
+ bool tc = false, bool fc = false)
+ : BBI(b), Kind(k), NumDups(d), NumDups2(d2), NeedSubsumption(s),
+ TClobbersPred(tc), FClobbersPred(fc) {}
};
/// Results of if-conversion feasibility analysis indexed by basic block
@@ -203,15 +207,21 @@ namespace {
bool FalseBranch, unsigned &Dups,
BranchProbability Prediction) const;
bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
- unsigned &Dups1, unsigned &Dups2) const;
+ unsigned &Dups1, unsigned &Dups2,
+ BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const;
void AnalyzeBranches(BBInfo &BBI);
void ScanInstructions(BBInfo &BBI,
MachineBasicBlock::iterator &Begin,
MachineBasicBlock::iterator &End) const;
+ bool RescanInstructions(
+ MachineBasicBlock::iterator &TIB, MachineBasicBlock::iterator &FIB,
+ MachineBasicBlock::iterator &TIE, MachineBasicBlock::iterator &FIE,
+ BBInfo &TrueBBI, BBInfo &FalseBBI) const;
void AnalyzeBlock(MachineBasicBlock &MBB,
std::vector<std::unique_ptr<IfcvtToken>> &Tokens);
bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
- bool isTriangle = false, bool RevBranch = false);
+ bool isTriangle = false, bool RevBranch = false,
+ bool hasCommonTail = false);
void AnalyzeBlocks(MachineFunction &MF,
std::vector<std::unique_ptr<IfcvtToken>> &Tokens);
void InvalidatePreds(MachineBasicBlock &MBB);
@@ -219,7 +229,8 @@ namespace {
bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
- unsigned NumDups1, unsigned NumDups2);
+ unsigned NumDups1, unsigned NumDups2,
+ bool TClobbers, bool FClobbers);
void PredicateBlock(BBInfo &BBI,
MachineBasicBlock::iterator E,
SmallVectorImpl<MachineOperand> &Cond,
@@ -406,7 +417,9 @@ bool IfConverter::runOnMachineFunction(M
DEBUG(dbgs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
<< BBI.TrueBB->getNumber() << ",F:"
<< BBI.FalseBB->getNumber() << ") ");
- RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
+ RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2,
+ Token->TClobbersPred,
+ Token->FClobbersPred);
DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
if (RetVal) ++NumDiamonds;
break;
@@ -677,10 +690,36 @@ static void countDuplicatedInstructions(
}
}
+/// RescanInstructions - Run ScanInstructions on a pair of blocks.
+/// @param TIB - True Iterator Begin, points to first non-shared instruction
+/// @param FIB - False Iterator Begin, points to first non-shared instruction
+/// @param TIE - True Iterator End, points past last non-shared instruction
+/// @param FIE - False Iterator End, points past last non-shared instruction
+/// @param TrueBBI - BBInfo to update for the true block.
+/// @param FalseBBI - BBInfo to update for the false block.
+/// @returns - false if either block cannot be predicated or if both blocks end
+/// with a predicate-clobbering instruction.
+bool IfConverter::RescanInstructions(
+ MachineBasicBlock::iterator &TIB, MachineBasicBlock::iterator &FIB,
+ MachineBasicBlock::iterator &TIE, MachineBasicBlock::iterator &FIE,
+ BBInfo &TrueBBI, BBInfo &FalseBBI) const {
+ ScanInstructions(TrueBBI, TIB, TIE);
+ if (TrueBBI.IsUnpredicable)
+ return false;
+ ScanInstructions(FalseBBI, FIB, FIE);
+ if (FalseBBI.IsUnpredicable)
+ return false;
+ if (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred)
+ return false;
+ return true;
+}
+
/// 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,
- unsigned &Dups1, unsigned &Dups2) const {
+bool IfConverter::ValidDiamond(
+ BBInfo &TrueBBI, BBInfo &FalseBBI,
+ unsigned &Dups1, unsigned &Dups2,
+ BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const {
Dups1 = Dups2 = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
@@ -701,8 +740,7 @@ bool IfConverter::ValidDiamond(BBInfo &T
return false;
// FIXME: Allow true block to have an early exit?
- if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
- (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
+ if (TrueBBI.FalseBB || FalseBBI.FalseBB)
return false;
// Count duplicate instructions at the beginning and end of the true and
@@ -714,6 +752,16 @@ bool IfConverter::ValidDiamond(BBInfo &T
countDuplicatedInstructions(TIB, FIB, TIE, FIE, Dups1, Dups2,
*TrueBBI.BB, *FalseBBI.BB,
/* SkipConditionalBranches */ true);
+
+ TrueBBICalc.BB = TrueBBI.BB;
+ FalseBBICalc.BB = FalseBBI.BB;
+ if (!RescanInstructions(TIB, FIB, TIE, FIE, TrueBBICalc, FalseBBICalc))
+ return false;
+ // The size is used to decide whether to if-convert, and the shared portions
+ // are subtracted off. Because of the subtraction, we just use the size that
+ // was calculated by the original ScanInstructions, as it is correct.
+ TrueBBICalc.NonPredSize = TrueBBI.NonPredSize;
+ FalseBBICalc.NonPredSize = FalseBBI.NonPredSize;
return true;
}
@@ -841,11 +889,22 @@ void IfConverter::ScanInstructions(BBInf
/// Determine if the block is a suitable candidate to be predicated by the
/// specified predicate.
+/// @param BBI BBInfo for the block to check
+/// @param Pred Predicate array for the branch that leads to BBI
+/// @param isTriangle true if the Analysis is for a triangle
+/// @param RevBranch true if Reverse(Pred) leads to BBI (e.g. BBI is the false
+/// case
+/// @param hasCommonTail true if BBI shares a tail with a sibling block that
+/// contains any instruction that would make the block unpredicable.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
SmallVectorImpl<MachineOperand> &Pred,
- bool isTriangle, bool RevBranch) {
+ bool isTriangle, bool RevBranch,
+ bool hasCommonTail) {
// If the block is dead or unpredicable, then it cannot be predicated.
- if (BBI.IsDone || BBI.IsUnpredicable)
+ // Two blocks may share a common unpredicable tail, but this doesn't prevent
+ // them from being if-converted. The non-shared portion is assumed to have
+ // been checked
+ if (BBI.IsDone || (BBI.IsUnpredicable && !hasCommonTail))
return false;
// If it is already predicated but we couldn't analyze its terminator, the
@@ -859,7 +918,7 @@ bool IfConverter::FeasibilityAnalysis(BB
if (BBI.Predicate.size() && !TII->SubsumesPredicate(Pred, BBI.Predicate))
return false;
- if (BBI.BrCond.size()) {
+ if (!hasCommonTail && BBI.BrCond.size()) {
if (!isTriangle)
return false;
@@ -966,25 +1025,37 @@ void IfConverter::AnalyzeBlock(
BranchProbability Prediction = MBPI->getEdgeProbability(BB, TrueBBI.BB);
- if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
+ if (CanRevCond) {
+ BBInfo TrueBBICalc, FalseBBICalc;
+ if (ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2,
+ TrueBBICalc, FalseBBICalc) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, (TrueBBI.NonPredSize - (Dups + Dups2) +
- TrueBBI.ExtraCost), TrueBBI.ExtraCost2,
+ TrueBBICalc.ExtraCost),
+ TrueBBICalc.ExtraCost2,
*FalseBBI.BB, (FalseBBI.NonPredSize - (Dups + Dups2) +
- FalseBBI.ExtraCost),FalseBBI.ExtraCost2,
- Prediction) &&
- FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
- FeasibilityAnalysis(FalseBBI, RevCond)) {
- // Diamond:
- // EBB
- // / \_
- // | |
- // TBB FBB
- // \ /
- // TailBB
- // Note TailBB can be empty.
- Tokens.push_back(llvm::make_unique<IfcvtToken>(
- BBI, ICDiamond, TNeedSub | FNeedSub, Dups, Dups2));
- Enqueued = true;
+ FalseBBICalc.ExtraCost),
+ FalseBBICalc.ExtraCost2,
+ Prediction) &&
+ FeasibilityAnalysis(TrueBBI, BBI.BrCond,
+ /* IsTriangle */ false, /* RevCond */ false,
+ /* hasCommonTail */ true) &&
+ FeasibilityAnalysis(FalseBBI, RevCond,
+ /* IsTriangle */ false, /* RevCond */ false,
+ /* hasCommonTail */ true)) {
+ // Diamond:
+ // EBB
+ // / \_
+ // | |
+ // TBB FBB
+ // \ /
+ // TailBB
+ // Note TailBB can be empty.
+ Tokens.push_back(llvm::make_unique<IfcvtToken>(
+ BBI, ICDiamond, TNeedSub | FNeedSub, Dups, Dups2,
+ (bool) TrueBBICalc.ClobbersPred,
+ (bool) FalseBBICalc.ClobbersPred));
+ Enqueued = true;
+ }
}
if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction) &&
@@ -1429,8 +1500,18 @@ bool IfConverter::IfConvertTriangle(BBIn
}
/// If convert a diamond sub-CFG.
+/// \p BBI is the head of the diamond
+/// \p NumDups1 - number of shared instructions at the beginning of TrueBBI and
+/// FalseBBI
+/// \p NumDups2 - number of shared instructions at the end of TrueBBI and
+/// FalseBBI
+/// \p TClobbersPred - True if the true block clobbers the predicate in the
+/// non-shared portion.
+/// \p TClobbersPred - True if the false block clobbers the predicate in the
+/// non-shared portion.
bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
- unsigned NumDups1, unsigned NumDups2) {
+ unsigned NumDups1, unsigned NumDups2,
+ bool TClobbersPred, bool FClobbersPred) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
MachineBasicBlock *TailBB = TrueBBI.TrueBB;
@@ -1468,9 +1549,9 @@ bool IfConverter::IfConvertDiamond(BBInf
// Figure out the more profitable ordering.
bool DoSwap = false;
- if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
+ if (TClobbersPred && !FClobbersPred)
DoSwap = true;
- else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
+ else if (TClobbersPred == FClobbersPred) {
if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
DoSwap = true;
}
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