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author | Dan Gohman <gohman@apple.com> | 2010-01-21 22:42:49 +0000 |
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committer | Dan Gohman <gohman@apple.com> | 2010-01-21 22:42:49 +0000 |
commit | 8b0ade3eb8281f9b332d5764cfe5c4ed3b2b32d8 (patch) | |
tree | bb2fd6686c3f2ba2b08dac5c10775f7936ed43b4 /lib/Transforms/Scalar | |
parent | 80ffc965f513bed2252316af8530c14c36c2e295 (diff) | |
download | external_llvm-8b0ade3eb8281f9b332d5764cfe5c4ed3b2b32d8.zip external_llvm-8b0ade3eb8281f9b332d5764cfe5c4ed3b2b32d8.tar.gz external_llvm-8b0ade3eb8281f9b332d5764cfe5c4ed3b2b32d8.tar.bz2 |
Prune the search for candidate formulae if the number of register
operands exceeds the number of registers used in the initial
solution, as that wouldn't lead to a profitable solution anyway.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94107 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Transforms/Scalar')
-rw-r--r-- | lib/Transforms/Scalar/LoopStrengthReduce.cpp | 99 |
1 files changed, 67 insertions, 32 deletions
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp index b7a733c..a5b4fa4 100644 --- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp +++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp @@ -1120,6 +1120,8 @@ public: const SmallVector<LSRUse, 16> &Uses, const Loop *L, ScalarEvolution &SE); + unsigned getNumRegs() const { return NumRegs; } + bool operator<(const Score &Other) const; void print_details(raw_ostream &OS, const SCEV *Reg, @@ -1383,6 +1385,11 @@ class LSRInstance { /// arbitrary index value to each register as a sort tie breaker. unsigned CurrentArbitraryRegIndex; + /// MaxNumRegs - To help prune the search for solutions, identify the number + /// of registers needed by the initial solution. No formula should require + /// more than this. + unsigned MaxNumRegs; + /// Factors - Interesting factors between use strides. SmallSetVector<int64_t, 4> Factors; @@ -1412,6 +1419,8 @@ class LSRInstance { void CountRegister(const SCEV *Reg, uint32_t Complexity, size_t LUIdx); void CountRegisters(const Formula &F, size_t LUIdx); + bool InsertFormula(LSRUse &LU, unsigned LUIdx, const Formula &F); + void GenerateSymbolicOffsetReuse(LSRUse &LU, unsigned LUIdx, Formula Base); void GenerateICmpZeroScaledReuse(LSRUse &LU, unsigned LUIdx, @@ -1913,6 +1922,23 @@ void LSRInstance::CountRegisters(const Formula &F, size_t LUIdx) { CountRegister(*I, Complexity, LUIdx); } +/// InsertFormula - If the given formula has not yet been inserted, add it +/// to the list, and return true. Return false otherwise. +bool LSRInstance::InsertFormula(LSRUse &LU, unsigned LUIdx, const Formula &F) { + // If a formula by itself would require more registers than the base solution, + // discard it and stop searching from it, as it won't be profitable. This is + // actually more permissive than it could be, because it doesn't include + // registers used by non-constant strides in F. + if (F.getNumRegs() > MaxNumRegs) + return false; + + if (!LU.InsertFormula(F)) + return false; + + CountRegisters(LU.Formulae.back(), LUIdx); + return true; +} + /// GenerateSymbolicOffsetReuse - Generate reuse formulae using symbolic /// offsets. void LSRInstance::GenerateSymbolicOffsetReuse(LSRUse &LU, unsigned LUIdx, @@ -1930,8 +1956,7 @@ void LSRInstance::GenerateSymbolicOffsetReuse(LSRUse &LU, unsigned LUIdx, if (!isLegalUse(F.AM, LU.Kind, LU.AccessTy, TLI)) continue; F.BaseRegs[i] = G; - if (LU.InsertFormula(F)) - CountRegisters(LU.Formulae.back(), LUIdx); + (void)InsertFormula(LU, LUIdx, F); } } @@ -1981,8 +2006,7 @@ void LSRInstance::GenerateICmpZeroScaledReuse(LSRUse &LU, unsigned LUIdx, } // If we make it here and it's legal, add it. - if (LU.InsertFormula(F)) - CountRegisters(LU.Formulae.back(), LUIdx); + (void)InsertFormula(LU, LUIdx, F); next:; } } @@ -2006,11 +2030,9 @@ LSRInstance::GenerateFormulaeFromReplacedBaseReg( E = AddOps.end(); I != E; ++I) F.BaseRegs.push_back(*I); F.AM.HasBaseReg = !F.BaseRegs.empty(); - if (LU.InsertFormula(F)) { - CountRegisters(LU.Formulae.back(), LUIdx); - // Recurse. + if (InsertFormula(LU, LUIdx, F)) + // If that formula hadn't been seen before, recurse to find more like it. GenerateReassociationReuse(LU, LUIdx, LU.Formulae.back()); - } } /// GenerateReassociationReuse - Split out subexpressions from adds and @@ -2095,8 +2117,7 @@ void LSRInstance::GenerateCombinationReuse(LSRUse &LU, unsigned LUIdx, } if (Ops.size() > 1) { F.BaseRegs.push_back(SE.getAddExpr(Ops)); - if (LU.InsertFormula(F)) - CountRegisters(LU.Formulae.back(), LUIdx); + (void)InsertFormula(LU, LUIdx, F); } } @@ -2144,8 +2165,7 @@ void LSRInstance::GenerateScaledReuse(LSRUse &LU, unsigned LUIdx, std::swap(NewF.BaseRegs[i], NewF.BaseRegs.back()); NewF.BaseRegs.pop_back(); NewF.AM.HasBaseReg = !NewF.BaseRegs.empty(); - if (LU.InsertFormula(NewF)) - CountRegisters(LU.Formulae.back(), LUIdx); + (void)InsertFormula(LU, LUIdx, NewF); } } } @@ -2174,8 +2194,7 @@ void LSRInstance::GenerateTruncateReuse(LSRUse &LU, unsigned LUIdx, for (SmallVectorImpl<const SCEV *>::iterator J = F.BaseRegs.begin(), JE = F.BaseRegs.end(); J != JE; ++J) *J = SE.getAnyExtendExpr(*J, SrcTy); - if (LU.InsertFormula(F)) - CountRegisters(LU.Formulae.back(), LUIdx); + (void)InsertFormula(LU, LUIdx, F); } } } @@ -2300,8 +2319,7 @@ void LSRInstance::GenerateConstantOffsetReuse() { const SCEV *Diff = SE.getAddExpr(NegImmS, NewF.ScaledReg); if (Diff->isZero()) continue; NewF.ScaledReg = Diff; - if (LU.InsertFormula(NewF)) - CountRegisters(LU.Formulae.back(), LUIdx); + (void)InsertFormula(LU, LUIdx, NewF); } // Use the immediate in a base register. for (size_t N = 0, NE = F.BaseRegs.size(); N != NE; ++N) { @@ -2320,8 +2338,7 @@ void LSRInstance::GenerateConstantOffsetReuse() { -(uint64_t)NewF.AM.BaseOffs))) continue; NewF.BaseRegs[N] = Diff; - if (LU.InsertFormula(NewF)) - CountRegisters(LU.Formulae.back(), LUIdx); + (void)InsertFormula(LU, LUIdx, NewF); } } } @@ -2358,8 +2375,19 @@ LSRInstance::GenerateAllReuseFormulae() { /// TODO: Should this give more weight to users inside the loop? void LSRInstance::GenerateLoopInvariantRegisterUses() { - for (size_t i = 0, e = RegSequence.size(); i != e; ++i) - if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(RegSequence[i])) { + SmallVector<const SCEV *, 8> Worklist(RegSequence.begin(), RegSequence.end()); + + while (!Worklist.empty()) { + const SCEV *S = Worklist.pop_back_val(); + + if (const SCEVNAryExpr *N = dyn_cast<SCEVNAryExpr>(S)) + Worklist.insert(Worklist.end(), N->op_begin(), N->op_end()); + else if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S)) + Worklist.push_back(C->getOperand()); + else if (const SCEVUDivExpr *D = dyn_cast<SCEVUDivExpr>(S)) { + Worklist.push_back(D->getLHS()); + Worklist.push_back(D->getRHS()); + } else if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) { const Value *V = U->getValue(); if (const Instruction *Inst = dyn_cast<Instruction>(V)) if (L->contains(Inst)) continue; @@ -2400,6 +2428,7 @@ LSRInstance::GenerateLoopInvariantRegisterUses() { CountRegisters(LU.Formulae.back(), Uses.size() - 1); } } + } } #ifndef NDEBUG @@ -2424,7 +2453,7 @@ LSRInstance::LSRInstance(const TargetLowering *tli, Loop *l, Pass *P) : IU(P->getAnalysis<IVUsers>()), SE(P->getAnalysis<ScalarEvolution>()), DT(P->getAnalysis<DominatorTree>()), - TLI(tli), L(l), Changed(false), CurrentArbitraryRegIndex(0) { + TLI(tli), L(l), Changed(false), CurrentArbitraryRegIndex(0), MaxNumRegs(0) { // If LoopSimplify form is not available, stay out of trouble. if (!L->isLoopSimplifyForm()) return; @@ -2538,15 +2567,24 @@ LSRInstance::LSRInstance(const TargetLowering *tli, Loop *l, Pass *P) if (Types.size() == 1) Types.clear(); - // Now use the reuse data to generate a bunch of interesting ways - // to formulate the values needed for the uses. - GenerateAllReuseFormulae(); - // If there are any uses of registers that we're tracking that have escaped // IVUsers' attention, add trivial uses for them, so that the register // voting process takes the into consideration. GenerateLoopInvariantRegisterUses(); + // Start by assuming we'll assign each use its own register. This is + // sometimes called "full" strength reduction, or "superhero" mode. + // Sometimes this is the best solution, but if there are opportunities for + // reuse we may find a better solution. + Score CurScore; + CurScore.RateInitial(Uses, L, SE); + + MaxNumRegs = CurScore.getNumRegs(); + + // Now use the reuse data to generate a bunch of interesting ways + // to formulate the values needed for the uses. + GenerateAllReuseFormulae(); + // Sort the formulae. TODO: This is redundantly sorted below. for (SmallVectorImpl<LSRUse>::iterator I = Uses.begin(), E = Uses.end(); I != E; ++I) { @@ -2559,13 +2597,6 @@ LSRInstance::LSRInstance(const TargetLowering *tli, Loop *l, Pass *P) // next step is to start looking at register reuse possibilities. DEBUG(print(dbgs()); dbgs() << '\n'); - // Start by assuming we'll assign each use its own register. This is - // sometimes called "full" strength reduction, or "superhero" mode. - // Sometimes this is the best solution, but if there are opportunities for - // reuse we may find a better solution. - Score CurScore; - CurScore.RateInitial(Uses, L, SE); - // Create a sorted list of registers with those with the most uses appearing // earlier in the list. We'll visit them first, as they're the most likely // to represent profitable reuse opportunities. @@ -2669,6 +2700,10 @@ LSRInstance::LSRInstance(const TargetLowering *tli, Loop *l, Pass *P) } void LSRInstance::print(raw_ostream &OS) const { + if (MaxNumRegs != 0) + OS << "LSR is considering " << MaxNumRegs << " to be the maximum " + "number of registers needed.\n"; + OS << "LSR has identified the following interesting factors and types: "; bool First = true; |