[llvm-commits] [llvm] r164682 - /llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
Hans Wennborg
hans at hanshq.net
Wed Sep 26 02:34:53 PDT 2012
Author: hans
Date: Wed Sep 26 04:34:53 2012
New Revision: 164682
URL: http://llvm.org/viewvc/llvm-project?rev=164682&view=rev
Log:
SimplifyCFG: Refactor the switch-to-lookup table transformation by
breaking out the building of lookup tables into a separate class.
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=164682&r1=164681&r2=164682&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Wed Sep 26 04:34:53 2012
@@ -3240,61 +3240,127 @@
return true;
}
-/// BuildLookupTable - Build a lookup table with the contents of Results, using
-/// DefaultResult to fill the holes in the table. If the table ends up
-/// containing the same result in each element, set *SingleResult to that value
-/// and return NULL.
-static GlobalVariable *BuildLookupTable(Module &M,
- uint64_t TableSize,
- ConstantInt *Offset,
- const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Results,
- Constant *DefaultResult,
- Constant **SingleResult) {
- assert(Results.size() && "Need values to build lookup table");
- assert(TableSize >= Results.size() && "Table needs to hold all values");
+namespace {
+ /// SwitchLookupTable - This class represents a lookup table that can be used
+ /// to replace a switch.
+ class SwitchLookupTable {
+ public:
+ /// SwitchLookupTable - Create a lookup table to use as a switch replacement
+ /// with the contents of Values, using DefaultValue to fill any holes in the
+ /// table.
+ SwitchLookupTable(Module &M,
+ uint64_t TableSize,
+ ConstantInt *Offset,
+ const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
+ Constant *DefaultValue);
+
+ /// BuildLookup - Build instructions with Builder to retrieve the value at
+ /// the position given by Index in the lookup table.
+ Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
+
+ private:
+ // Depending on the contents of the table, it can be represented in
+ // different ways.
+ enum {
+ // For tables where each element contains the same value, we just have to
+ // store that single value and return it for each lookup.
+ SingleValueKind,
+
+ // The table is stored as an array of values. Values are retrieved by load
+ // instructions from the table.
+ ArrayKind
+ } Kind;
+
+ // For SingleValueKind, this is the single value.
+ Constant *SingleValue;
+
+ // For ArrayKind, this is the array.
+ GlobalVariable *Array;
+ };
+}
+
+SwitchLookupTable::SwitchLookupTable(Module &M,
+ uint64_t TableSize,
+ ConstantInt *Offset,
+ const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
+ Constant *DefaultValue) {
+ assert(Values.size() && "Can't build lookup table without values.");
+ assert(TableSize >= Values.size() && "Can't fit values in table.");
// If all values in the table are equal, this is that value.
- Constant *SameResult = Results.begin()->second;
+ SingleValue = Values.begin()->second;
// Build up the table contents.
- std::vector<Constant*> TableContents(TableSize);
- for (size_t I = 0, E = Results.size(); I != E; ++I) {
- ConstantInt *CaseVal = Results[I].first;
- Constant *CaseRes = Results[I].second;
+ SmallVector<Constant*, 64> TableContents(TableSize);
+ for (size_t I = 0, E = Values.size(); I != E; ++I) {
+ ConstantInt *CaseVal = Values[I].first;
+ Constant *CaseRes = Values[I].second;
+ assert(CaseRes->getType() == DefaultValue->getType());
- uint64_t Idx = (CaseVal->getValue() - Offset->getValue()).getLimitedValue();
+ uint64_t Idx = (CaseVal->getValue() - Offset->getValue())
+ .getLimitedValue();
TableContents[Idx] = CaseRes;
- if (CaseRes != SameResult)
- SameResult = NULL;
+ if (CaseRes != SingleValue)
+ SingleValue = NULL;
}
// Fill in any holes in the table with the default result.
- if (Results.size() < TableSize) {
- for (unsigned i = 0; i < TableSize; ++i) {
- if (!TableContents[i])
- TableContents[i] = DefaultResult;
+ if (Values.size() < TableSize) {
+ for (uint64_t I = 0; I < TableSize; ++I) {
+ if (!TableContents[I])
+ TableContents[I] = DefaultValue;
}
- if (DefaultResult != SameResult)
- SameResult = NULL;
+ if (DefaultValue != SingleValue)
+ SingleValue = NULL;
}
- // Same result was used in the entire table; just return that.
- if (SameResult) {
- *SingleResult = SameResult;
- return NULL;
+ // If each element in the table contains the same value, we only need to store
+ // that single value.
+ if (SingleValue) {
+ Kind = SingleValueKind;
+ return;
}
- ArrayType *ArrayTy = ArrayType::get(DefaultResult->getType(), TableSize);
+ // Store the table in an array.
+ ArrayType *ArrayTy = ArrayType::get(DefaultValue->getType(), TableSize);
Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
- GlobalVariable *GV = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
- GlobalVariable::PrivateLinkage,
- Initializer,
- "switch.table");
- GV->setUnnamedAddr(true);
- return GV;
+ Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
+ GlobalVariable::PrivateLinkage,
+ Initializer,
+ "switch.table");
+ Array->setUnnamedAddr(true);
+ Kind = ArrayKind;
+}
+
+Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
+ switch (Kind) {
+ case SingleValueKind:
+ return SingleValue;
+ case ArrayKind: {
+ Value *GEPIndices[] = { Builder.getInt32(0), Index };
+ Value *GEP = Builder.CreateInBoundsGEP(Array, GEPIndices,
+ "switch.gep");
+ return Builder.CreateLoad(GEP, "switch.load");
+ }
+ }
+ llvm_unreachable("Unknown lookup table kind!");
+}
+
+/// ShouldBuildLookupTable - Determine whether a lookup table should be built
+/// for this switch, based on the number of caes, size of the table and the
+/// types of the results.
+static bool ShouldBuildLookupTable(SwitchInst *SI,
+ uint64_t TableSize) {
+ // The table density should be at least 40%. This is the same criterion as for
+ // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
+ // FIXME: Find the best cut-off.
+ if (SI->getNumCases() * 10 >= TableSize * 4)
+ return true;
+
+ return false;
}
/// SwitchToLookupTable - If the switch is only used to initialize one or more
@@ -3316,7 +3382,7 @@
// GEP needs a runtime relocation in PIC code. We should just build one big
// string and lookup indices into that.
- // Ignore the switch if the number of cases are too small.
+ // Ignore the switch if the number of cases is too small.
// This is similar to the check when building jump tables in
// SelectionDAGBuilder::handleJTSwitchCase.
// FIXME: Determine the best cut-off.
@@ -3370,33 +3436,16 @@
}
APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
- // The table density should be at lest 40%. This is the same criterion as for
- // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
- // FIXME: Find the best cut-off.
- // Be careful to avoid overlow in the density computation.
+ // Be careful to avoid overflow when TableSize is used in
+ // ShouldBuildLookupTable.
if (RangeSpread.zextOrSelf(64).ugt(UINT64_MAX / 4 - 1))
return false;
uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
- if (SI->getNumCases() * 10 < TableSize * 4)
+ if (!ShouldBuildLookupTable(SI, TableSize))
return false;
- // Build the lookup tables.
- SmallDenseMap<PHINode*, GlobalVariable*> LookupTables;
- SmallDenseMap<PHINode*, Constant*> SingleResults;
-
- Module &Mod = *CommonDest->getParent()->getParent();
- for (SmallVector<PHINode*, 4>::iterator I = PHIs.begin(), E = PHIs.end();
- I != E; ++I) {
- PHINode *PHI = *I;
-
- Constant *SingleResult = NULL;
- LookupTables[PHI] = BuildLookupTable(Mod, TableSize, MinCaseVal,
- ResultLists[PHI], DefaultResults[PHI],
- &SingleResult);
- SingleResults[PHI] = SingleResult;
- }
-
// Create the BB that does the lookups.
+ Module &Mod = *CommonDest->getParent()->getParent();
BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(),
"switch.lookup",
CommonDest->getParent(),
@@ -3414,19 +3463,13 @@
// Populate the BB that does the lookups.
Builder.SetInsertPoint(LookupBB);
bool ReturnedEarly = false;
- for (SmallVector<PHINode*, 4>::iterator I = PHIs.begin(), E = PHIs.end();
- I != E; ++I) {
- PHINode *PHI = *I;
- // There was a single result for this phi; just use that.
- if (Constant *SingleResult = SingleResults[PHI]) {
- PHI->addIncoming(SingleResult, LookupBB);
- continue;
- }
+ for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
+ PHINode *PHI = PHIs[I];
+
+ SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultLists[PHI],
+ DefaultResults[PHI]);
- Value *GEPIndices[] = { Builder.getInt32(0), TableIndex };
- Value *GEP = Builder.CreateInBoundsGEP(LookupTables[PHI], GEPIndices,
- "switch.gep");
- Value *Result = Builder.CreateLoad(GEP, "switch.load");
+ Value *Result = Table.BuildLookup(TableIndex, Builder);
// If the result is used to return immediately from the function, we want to
// do that right here.
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