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move the "br (X == 0 | X == 1), T, F" -> switch optimization to a new 

location in simplifycfg.  In the old days, SimplifyCFG was never run on
the entry block, so we had to scan over all preds of the BB passed into
simplifycfg to do this xform, now we can just check blocks ending with
a condbranch.  This avoids a scan over all preds of every simplified 
block, which should be a significant compile-time perf win on functions
with lots of edges.  No functionality change.

llvm-svn: 121668
This commit is contained in:
Chris Lattner 2010-12-13 01:57:34 +00:00
parent 4088e2b8e4
commit 1475987634
1 changed files with 56 additions and 57 deletions
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113
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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@ -44,7 +44,7 @@ class SimplifyCFGOpt {
ConstantInt *GetConstantInt(Value *V);
Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values);
Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values);
bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
bool GatherValueComparisons(Value *Cond, Value *&CompVal,
std::vector<ConstantInt*> &Values);
Value *isValueEqualityComparison(TerminatorInst *TI);
BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
@ -353,8 +353,11 @@ GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values) {
/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
/// bunch of comparisons of one value against constants, return the value and
/// the constants being compared.
bool SimplifyCFGOpt::GatherValueComparisons(Instruction *Cond, Value *&CompVal,
bool SimplifyCFGOpt::GatherValueComparisons(Value *CondV, Value *&CompVal,
std::vector<ConstantInt*> &Values) {
Instruction *Cond = dyn_cast<Instruction>(CondV);
if (Cond == 0) return false;
if (Cond->getOpcode() == Instruction::Or) {
CompVal = GatherConstantSetEQs(Cond, Values);
@ -1970,6 +1973,57 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
if (PBI != BI && PBI->isConditional())
if (SimplifyCondBranchToCondBranch(PBI, BI))
return SimplifyCFG(BB) | true;
// Change br (X == 0 | X == 1), T, F into a switch instruction.
// If this is a bunch of seteq's or'd together, or if it's a bunch of
// 'setne's and'ed together, collect them.
Value *CompVal = 0;
std::vector<ConstantInt*> Values;
bool TrueWhenEqual = GatherValueComparisons(BI->getCondition(), CompVal,
Values);
if (CompVal) {
// There might be duplicate constants in the list, which the switch
// instruction can't handle, remove them now.
std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
// Figure out which block is which destination.
BasicBlock *DefaultBB = BI->getSuccessor(1);
BasicBlock *EdgeBB = BI->getSuccessor(0);
if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
// Convert pointer to int before we switch.
if (CompVal->getType()->isPointerTy()) {
assert(TD && "Cannot switch on pointer without TargetData");
CompVal = new PtrToIntInst(CompVal,
TD->getIntPtrType(CompVal->getContext()),
"magicptr", BI);
}
// Create the new switch instruction now.
SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
Values.size(), BI);
// Add all of the 'cases' to the switch instruction.
for (unsigned i = 0, e = Values.size(); i != e; ++i)
New->addCase(Values[i], EdgeBB);
// We added edges from PI to the EdgeBB. As such, if there were any
// PHI nodes in EdgeBB, they need entries to be added corresponding to
// the number of edges added.
for (BasicBlock::iterator BBI = EdgeBB->begin();
isa<PHINode>(BBI); ++BBI) {
PHINode *PN = cast<PHINode>(BBI);
Value *InVal = PN->getIncomingValueForBlock(BB);
for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
PN->addIncoming(InVal, BB);
}
// Erase the old branch instruction.
EraseTerminatorInstAndDCECond(BI);
return true;
}
}
} else if (isa<UnreachableInst>(BB->getTerminator())) {
// If there are any instructions immediately before the unreachable that can
@ -2179,61 +2233,6 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
}
}
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator());
// Change br (X == 0 | X == 1), T, F into a switch instruction.
if (BI && BI->isConditional() && isa<Instruction>(BI->getCondition())) {
Instruction *Cond = cast<Instruction>(BI->getCondition());
// If this is a bunch of seteq's or'd together, or if it's a bunch of
// 'setne's and'ed together, collect them.
Value *CompVal = 0;
std::vector<ConstantInt*> Values;
bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
if (CompVal) {
// There might be duplicate constants in the list, which the switch
// instruction can't handle, remove them now.
std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
// Figure out which block is which destination.
BasicBlock *DefaultBB = BI->getSuccessor(1);
BasicBlock *EdgeBB = BI->getSuccessor(0);
if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
// Convert pointer to int before we switch.
if (CompVal->getType()->isPointerTy()) {
assert(TD && "Cannot switch on pointer without TargetData");
CompVal = new PtrToIntInst(CompVal,
TD->getIntPtrType(CompVal->getContext()),
"magicptr", BI);
}
// Create the new switch instruction now.
SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
Values.size(), BI);
// Add all of the 'cases' to the switch instruction.
for (unsigned i = 0, e = Values.size(); i != e; ++i)
New->addCase(Values[i], EdgeBB);
// We added edges from PI to the EdgeBB. As such, if there were any
// PHI nodes in EdgeBB, they need entries to be added corresponding to
// the number of edges added.
for (BasicBlock::iterator BBI = EdgeBB->begin();
isa<PHINode>(BBI); ++BBI) {
PHINode *PN = cast<PHINode>(BBI);
Value *InVal = PN->getIncomingValueForBlock(*PI);
for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
PN->addIncoming(InVal, *PI);
}
// Erase the old branch instruction.
EraseTerminatorInstAndDCECond(BI);
return true;
}
}
}
return Changed;
}