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[Constant Hoisting] Lazily compute the idom and cache the result.

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Related to <rdar://problem/16381500>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204434 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Juergen Ributzka 2014-03-21 06:04:39 +00:00
parent 8ebaf63750
commit 337eb3adbe
1 changed files with 43 additions and 4 deletions
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47
lib/Transforms/Scalar/ConstantHoisting.cpp
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@ -87,9 +87,10 @@ struct ConstantCandidate {
struct RebasedConstantInfo {
ConstantUseListType Uses;
Constant *Offset;
mutable BasicBlock *IDom;
RebasedConstantInfo(ConstantUseListType &&Uses, Constant *Offset)
: Uses(Uses), Offset(Offset) { }
: Uses(Uses), Offset(Offset), IDom(nullptr) { }
};
/// \brief A base constant and all its rebased constants.
@ -152,6 +153,17 @@ private:
Entry = nullptr;
}
/// \brief Find the common dominator of all uses and cache the result for
/// future lookup.
BasicBlock *getIDom(const RebasedConstantInfo &RCI) const {
if (RCI.IDom)
return RCI.IDom;
RCI.IDom = findIDomOfAllUses(RCI.Uses);
assert(RCI.IDom && "Invalid IDom.");
return RCI.IDom;
}
BasicBlock *findIDomOfAllUses(const ConstantUseListType &Uses) const;
Instruction *findMatInsertPt(Instruction *Inst, unsigned Idx = ~0U) const;
Instruction *findConstantInsertionPoint(const ConstantInfo &ConstInfo) const;
void collectConstantCandidates(Instruction *Inst, unsigned Idx,
@ -202,6 +214,32 @@ bool ConstantHoisting::runOnFunction(Function &Fn) {
return MadeChange;
}
/// \brief Find nearest common dominator of all uses.
/// FIXME: Replace this with NearestCommonDominator once it is in common code.
BasicBlock *
ConstantHoisting::findIDomOfAllUses(const ConstantUseListType &Uses) const {
// Collect all basic blocks.
SmallPtrSet<BasicBlock *, 8> BBs;
for (auto const &U : Uses)
BBs.insert(findMatInsertPt(U.Inst, U.OpndIdx)->getParent());
if (BBs.count(Entry))
return Entry;
while (BBs.size() >= 2) {
BasicBlock *BB, *BB1, *BB2;
BB1 = *BBs.begin();
BB2 = *std::next(BBs.begin());
BB = DT->findNearestCommonDominator(BB1, BB2);
if (BB == Entry)
return Entry;
BBs.erase(BB1);
BBs.erase(BB2);
BBs.insert(BB);
}
assert((BBs.size() == 1) && "Expected only one element.");
return *BBs.begin();
}
/// \brief Find the constant materialization insertion point.
Instruction *ConstantHoisting::findMatInsertPt(Instruction *Inst,
@ -224,11 +262,12 @@ Instruction *ConstantHoisting::findMatInsertPt(Instruction *Inst,
Instruction *ConstantHoisting::
findConstantInsertionPoint(const ConstantInfo &ConstInfo) const {
assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry.");
// Collect all basic blocks.
// Collect all IDoms.
SmallPtrSet<BasicBlock *, 8> BBs;
for (auto const &RCI : ConstInfo.RebasedConstants)
for (auto const &U : RCI.Uses)
BBs.insert(U.Inst->getParent());
BBs.insert(getIDom(RCI));
assert(!BBs.empty() && "No dominators!?");
if (BBs.count(Entry))
return &Entry->front();