#define DEBUG_TYPE "simplifycfg"
#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Constants.h"
-#include "llvm/DataLayout.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/GlobalVariable.h"
-#include "llvm/IRBuilder.h"
-#include "llvm/Instructions.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/MDBuilder.h"
-#include "llvm/Metadata.h"
-#include "llvm/Module.h"
-#include "llvm/Operator.h"
-#include "llvm/Type.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/IR/Type.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ConstantRange.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/NoFolder.h"
#include "llvm/Support/raw_ostream.h"
-#include "llvm/TargetTransformInfo.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <algorithm>
-#include <set>
#include <map>
+#include <set>
using namespace llvm;
static cl::opt<unsigned>
};
class SimplifyCFGOpt {
+ const TargetTransformInfo &TTI;
const DataLayout *const TD;
- const TargetTransformInfo *const TTI;
Value *isValueEqualityComparison(TerminatorInst *TI);
BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
public:
- SimplifyCFGOpt(const DataLayout *td, const TargetTransformInfo *tti)
- : TD(td), TTI(tti) {}
+ SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout *TD)
+ : TTI(TTI), TD(TD) {}
bool run(BasicBlock *BB);
};
}
if (PredHasWeights) {
GetBranchWeights(PTI, Weights);
- // branch-weight metadata is inconsistant here.
+ // branch-weight metadata is inconsistent here.
if (Weights.size() != 1 + PredCases.size())
PredHasWeights = SuccHasWeights = false;
} else if (SuccHasWeights)
SmallVector<uint64_t, 8> SuccWeights;
if (SuccHasWeights) {
GetBranchWeights(TI, SuccWeights);
- // branch-weight metadata is inconsistant here.
+ // branch-weight metadata is inconsistent here.
if (SuccWeights.size() != 1 + BBCases.size())
PredHasWeights = SuccHasWeights = false;
} else if (PredHasWeights)
return Changed;
}
-/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
-/// and an BB2 and the only successor of BB1 is BB2, hoist simple code
-/// (for now, restricted to a single instruction that's side effect free) from
-/// the BB1 into the branch block to speculatively execute it.
+/// \brief Speculate a conditional basic block flattening the CFG.
+///
+/// Note that this is a very risky transform currently. Speculating
+/// instructions like this is most often not desirable. Instead, there is an MI
+/// pass which can do it with full awareness of the resource constraints.
+/// However, some cases are "obvious" and we should do directly. An example of
+/// this is speculating a single, reasonably cheap instruction.
+///
+/// There is only one distinct advantage to flattening the CFG at the IR level:
+/// it makes very common but simplistic optimizations such as are common in
+/// instcombine and the DAG combiner more powerful by removing CFG edges and
+/// modeling their effects with easier to reason about SSA value graphs.
///
-/// Turn
-/// BB:
-/// %t1 = icmp
-/// br i1 %t1, label %BB1, label %BB2
-/// BB1:
-/// %t3 = add %t2, c
+///
+/// An illustration of this transform is turning this IR:
+/// \code
+/// BB:
+/// %cmp = icmp ult %x, %y
+/// br i1 %cmp, label %EndBB, label %ThenBB
+/// ThenBB:
+/// %sub = sub %x, %y
/// br label BB2
-/// BB2:
-/// =>
-/// BB:
-/// %t1 = icmp
-/// %t4 = add %t2, c
-/// %t3 = select i1 %t1, %t2, %t3
+/// EndBB:
+/// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
+/// ...
+/// \endcode
+///
+/// Into this IR:
+/// \code
+/// BB:
+/// %cmp = icmp ult %x, %y
+/// %sub = sub %x, %y
+/// %cond = select i1 %cmp, 0, %sub
+/// ...
+/// \endcode
+///
+/// \returns true if the conditional block is removed.
static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
// Only speculatively execution a single instruction (not counting the
// terminator) for now.
if (BB1V == BIParentV)
continue;
- // Check for saftey.
+ // Check for safety.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) {
// An unfolded ConstantExpr could end up getting expanded into
// Instructions. Don't speculate this and another instruction at
///
/// We prefer to split the edge to 'end' so that there is a true/false entry to
/// the PHI, merging the third icmp into the switch.
-static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
- const DataLayout *TD,
- IRBuilder<> &Builder) {
+static bool TryToSimplifyUncondBranchWithICmpInIt(
+ ICmpInst *ICI, IRBuilder<> &Builder, const TargetTransformInfo &TTI,
+ const DataLayout *TD) {
BasicBlock *BB = ICI->getParent();
// If the block has any PHIs in it or the icmp has multiple uses, it is too
ICI->eraseFromParent();
}
// BB is now empty, so it is likely to simplify away.
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
}
// Ok, the block is reachable from the default dest. If the constant we're
ICI->replaceAllUsesWith(V);
ICI->eraseFromParent();
// BB is now empty, so it is likely to simplify away.
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
}
// The use of the icmp has to be in the 'end' block, by the only PHI node in
ConstantInt *Offset,
const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
Constant *DefaultValue,
- const DataLayout *TD) {
+ const DataLayout *TD)
+ : SingleValue(0), BitMap(0), BitMapElementTy(0), Array(0) {
assert(Values.size() && "Can't build lookup table without values!");
assert(TableSize >= Values.size() && "Can't fit values in table!");
/// types of the results.
static bool ShouldBuildLookupTable(SwitchInst *SI,
uint64_t TableSize,
+ const TargetTransformInfo &TTI,
const DataLayout *TD,
const SmallDenseMap<PHINode*, Type*>& ResultTypes) {
- // 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() > TableSize || TableSize >= UINT64_MAX / 10)
return false; // TableSize overflowed, or mul below might overflow.
- if (SI->getNumCases() * 10 >= TableSize * 4)
- return true;
- // If each table would fit in a register, we should build it anyway.
+ bool AllTablesFitInRegister = true;
+ bool HasIllegalType = false;
for (SmallDenseMap<PHINode*, Type*>::const_iterator I = ResultTypes.begin(),
E = ResultTypes.end(); I != E; ++I) {
- if (!SwitchLookupTable::WouldFitInRegister(TD, TableSize, I->second))
- return false;
+ Type *Ty = I->second;
+
+ // Saturate this flag to true.
+ HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty);
+
+ // Saturate this flag to false.
+ AllTablesFitInRegister = AllTablesFitInRegister &&
+ SwitchLookupTable::WouldFitInRegister(TD, TableSize, Ty);
+
+ // If both flags saturate, we're done. NOTE: This *only* works with
+ // saturating flags, and all flags have to saturate first due to the
+ // non-deterministic behavior of iterating over a dense map.
+ if (HasIllegalType && !AllTablesFitInRegister)
+ break;
}
- return true;
+
+ // If each table would fit in a register, we should build it anyway.
+ if (AllTablesFitInRegister)
+ return true;
+
+ // Don't build a table that doesn't fit in-register if it has illegal types.
+ if (HasIllegalType)
+ return false;
+
+ // 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.
+ return SI->getNumCases() * 10 >= TableSize * 4;
}
/// SwitchToLookupTable - If the switch is only used to initialize one or more
/// replace the switch with lookup tables.
static bool SwitchToLookupTable(SwitchInst *SI,
IRBuilder<> &Builder,
- const DataLayout* TD,
- const TargetTransformInfo *TTI) {
+ const TargetTransformInfo &TTI,
+ const DataLayout* TD) {
assert(SI->getNumCases() > 1 && "Degenerate switch?");
// Only build lookup table when we have a target that supports it.
- if (!TTI || !TTI->getScalarTargetTransformInfo()->shouldBuildLookupTables())
+ if (!TTI.shouldBuildLookupTables())
return false;
// FIXME: If the switch is too sparse for a lookup table, perhaps we could
APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
- if (!ShouldBuildLookupTable(SI, TableSize, TD, ResultTypes))
+ if (!ShouldBuildLookupTable(SI, TableSize, TTI, TD, ResultTypes))
return false;
// Create the BB that does the lookups.
// see if that predecessor totally determines the outcome of this switch.
if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
Value *Cond = SI->getCondition();
if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
if (SimplifySwitchOnSelect(SI, Select))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
// If the block only contains the switch, see if we can fold the block
// away into any preds.
++BBI;
if (SI == &*BBI)
if (FoldValueComparisonIntoPredecessors(SI, Builder))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
}
// Try to transform the switch into an icmp and a branch.
if (TurnSwitchRangeIntoICmp(SI, Builder))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
// Remove unreachable cases.
if (EliminateDeadSwitchCases(SI))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
if (ForwardSwitchConditionToPHI(SI))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
- if (SwitchToLookupTable(SI, Builder, TD, TTI))
- return SimplifyCFG(BB) | true;
+ if (SwitchToLookupTable(SI, Builder, TTI, TD))
+ return SimplifyCFG(BB, TTI, TD) | true;
return false;
}
if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
if (SimplifyIndirectBrOnSelect(IBI, SI))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
}
return Changed;
}
for (++I; isa<DbgInfoIntrinsic>(I); ++I)
;
if (I->isTerminator() &&
- TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
+ TryToSimplifyUncondBranchWithICmpInIt(ICI, Builder, TTI, TD))
return true;
}
// predecessor and use logical operations to update the incoming value
// for PHI nodes in common successor.
if (FoldBranchToCommonDest(BI))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
return false;
}
// switch.
if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
// This block must be empty, except for the setcond inst, if it exists.
// Ignore dbg intrinsics.
++I;
if (&*I == BI) {
if (FoldValueComparisonIntoPredecessors(BI, Builder))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
} else if (&*I == cast<Instruction>(BI->getCondition())){
++I;
// Ignore dbg intrinsics.
while (isa<DbgInfoIntrinsic>(I))
++I;
if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
}
}
// branches to us and one of our successors, fold the comparison into the
// predecessor and use logical operations to pick the right destination.
if (FoldBranchToCommonDest(BI))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
// We have a conditional branch to two blocks that are only reachable
// from BI. We know that the condbr dominates the two blocks, so see if
if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
if (HoistThenElseCodeToIf(BI))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
} else {
// If Successor #1 has multiple preds, we may be able to conditionally
// execute Successor #0 if it branches to successor #1.
if (Succ0TI->getNumSuccessors() == 1 &&
Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
}
} else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
// If Successor #0 has multiple preds, we may be able to conditionally
if (Succ1TI->getNumSuccessors() == 1 &&
Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
}
// If this is a branch on a phi node in the current block, thread control
if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
if (PN->getParent() == BI->getParent())
if (FoldCondBranchOnPHI(BI, TD))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
// Scan predecessor blocks for conditional branches.
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
if (PBI != BI && PBI->isConditional())
if (SimplifyCondBranchToCondBranch(PBI, BI))
- return SimplifyCFG(BB) | true;
+ return SimplifyCFG(BB, TTI, TD) | true;
return false;
}
/// eliminates unreachable basic blocks, and does other "peephole" optimization
/// of the CFG. It returns true if a modification was made.
///
-bool llvm::SimplifyCFG(BasicBlock *BB, const DataLayout *TD,
- const TargetTransformInfo *TTI) {
- return SimplifyCFGOpt(TD, TTI).run(BB);
+bool llvm::SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
+ const DataLayout *TD) {
+ return SimplifyCFGOpt(TTI, TD).run(BB);
}
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