forked from OSchip/llvm-project
Work in progress, cleaning up MergeFuncs.
Further clean up the comparison function by removing overly generalized "domains". Remove all understanding of ELF aliases and simplify folding code and comments. llvm-svn: 110434
This commit is contained in:
Nick Lewycky
parent
2667f1d409
commit
f216f69ad9
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@ -42,19 +42,6 @@
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// other doesn't. We should learn to peer through bitcasts without imposing bad
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// performance properties.
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//
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// * emit aliases for ELF
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//
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// ELF supports symbol aliases which are represented with GlobalAlias in the
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// Module, and we could emit them in the case that the addresses don't need to
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// be distinct. The problem is that not all object formats support equivalent
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// functionality. There's a few approaches to this problem;
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// a) teach codegen to lower global aliases to thunks on platforms which don't
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// support them.
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// b) always emit thunks, and create a separate thunk-to-alias pass which
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// runs on ELF systems. This has the added benefit of transforming other
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// thunks such as those produced by a C++ frontend into aliases when legal
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// to do so.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "mergefunc"
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@ -108,7 +95,7 @@ namespace {
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class FunctionComparator {
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public:
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FunctionComparator(TargetData *TD, Function *F1, Function *F2)
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: F1(F1), F2(F2), TD(TD) {}
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: F1(F1), F2(F2), TD(TD), IDMap1Count(0), IDMap2Count(0) {}
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// Compare - test whether the two functions have equivalent behaviour.
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bool Compare();
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@ -117,10 +104,6 @@ private:
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// Compare - test whether two basic blocks have equivalent behaviour.
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bool Compare(const BasicBlock *BB1, const BasicBlock *BB2);
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// getDomain - a value's domain is its parent function if it is specific to a
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// function, or NULL otherwise.
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const Function *getDomain(const Value *V) const;
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// Enumerate - Assign or look up previously assigned numbers for the two
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// values, and return whether the numbers are equal. Numbers are assigned in
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// the order visited.
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@ -134,6 +117,7 @@ private:
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// isEquivalentGEP - Compare two GEPs for equivalent pointer arithmetic.
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bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2);
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bool isEquivalentGEP(const GetElementPtrInst *GEP1,
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const GetElementPtrInst *GEP2) {
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return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2));
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@ -148,9 +132,8 @@ private:
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TargetData *TD;
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typedef DenseMap<const Value *, unsigned long> IDMap;
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IDMap Map;
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DenseMap<const Function *, IDMap> Domains;
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DenseMap<const Function *, unsigned long> DomainCount;
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IDMap Map1, Map2;
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unsigned long IDMap1Count, IDMap2Count;
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};
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}
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@ -171,8 +154,8 @@ static unsigned long ProfileFunction(const Function *F) {
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return ID.ComputeHash();
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}
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/// isEquivalentType - any two pointers are equivalent. Otherwise, standard
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/// type equivalence rules apply.
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/// isEquivalentType - any two pointers in the same address space are
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/// equivalent. Otherwise, standard type equivalence rules apply.
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bool FunctionComparator::isEquivalentType(const Type *Ty1,
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const Type *Ty2) const {
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if (Ty1 == Ty2)
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@ -259,6 +242,7 @@ bool FunctionComparator::isEquivalentType(const Type *Ty1,
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return ATy1->getNumElements() == ATy2->getNumElements() &&
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isEquivalentType(ATy1->getElementType(), ATy2->getElementType());
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}
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case Type::VectorTyID: {
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const VectorType *VTy1 = cast<VectorType>(Ty1);
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const VectorType *VTy2 = cast<VectorType>(Ty2);
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@ -355,19 +339,6 @@ bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1,
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return true;
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}
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/// getDomain - a value's domain is its parent function if it is specific to a
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/// function, or NULL otherwise.
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const Function *FunctionComparator::getDomain(const Value *V) const {
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if (const Argument *A = dyn_cast<Argument>(V)) {
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return A->getParent();
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} else if (const BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
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return BB->getParent();
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} else if (const Instruction *I = dyn_cast<Instruction>(V)) {
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return I->getParent()->getParent();
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}
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return NULL;
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}
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/// Enumerate - Compare two values used by the two functions under pair-wise
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/// comparison. If this is the first time the values are seen, they're added to
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/// the mapping so that we will detect mismatches on next use.
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@ -375,8 +346,9 @@ bool FunctionComparator::Enumerate(const Value *V1, const Value *V2) {
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// Check for function @f1 referring to itself and function @f2 referring to
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// itself, or referring to each other, or both referring to either of them.
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// They're all equivalent if the two functions are otherwise equivalent.
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if (V1 == F1 || V1 == F2)
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if (V2 == F1 || V2 == F2)
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if (V1 == F1 && V2 == F2)
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return true;
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if (V1 == F2 && V2 == F1)
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return true;
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// TODO: constant expressions with GEP or references to F1 or F2.
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@ -390,25 +362,13 @@ bool FunctionComparator::Enumerate(const Value *V1, const Value *V2) {
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IA1->getConstraintString() == IA2->getConstraintString();
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}
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// We enumerate constants globally and arguments, basic blocks or
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// instructions within the function they belong to.
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const Function *Domain1 = getDomain(V1);
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const Function *Domain2 = getDomain(V2);
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// The domains have to either be both NULL, or F1, F2.
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if (Domain1 != Domain2)
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if (Domain1 != F1 && Domain1 != F2)
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return false;
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IDMap &Map1 = Domains[Domain1];
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unsigned long &ID1 = Map1[V1];
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if (!ID1)
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ID1 = ++DomainCount[Domain1];
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ID1 = ++IDMap1Count;
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IDMap &Map2 = Domains[Domain2];
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unsigned long &ID2 = Map2[V2];
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if (!ID2)
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ID2 = ++DomainCount[Domain2];
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ID2 = ++IDMap2Count;
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return ID1 == ID2;
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}
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@ -503,20 +463,26 @@ bool FunctionComparator::Compare() {
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// artifact, this also means that unreachable blocks are ignored.
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SmallVector<const BasicBlock *, 8> F1BBs, F2BBs;
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SmallSet<const BasicBlock *, 128> VisitedBBs; // in terms of F1.
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F1BBs.push_back(&F1->getEntryBlock());
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F2BBs.push_back(&F2->getEntryBlock());
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VisitedBBs.insert(F1BBs[0]);
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while (!F1BBs.empty()) {
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const BasicBlock *F1BB = F1BBs.pop_back_val();
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const BasicBlock *F2BB = F2BBs.pop_back_val();
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if (!Enumerate(F1BB, F2BB) || !Compare(F1BB, F2BB))
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return false;
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const TerminatorInst *F1TI = F1BB->getTerminator();
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const TerminatorInst *F2TI = F2BB->getTerminator();
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assert(F1TI->getNumSuccessors() == F2TI->getNumSuccessors());
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for (unsigned i = 0, e = F1TI->getNumSuccessors(); i != e; ++i) {
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if (!VisitedBBs.insert(F1TI->getSuccessor(i)))
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continue;
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F1BBs.push_back(F1TI->getSuccessor(i));
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F2BBs.push_back(F2TI->getSuccessor(i));
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}
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@ -530,70 +496,24 @@ bool FunctionComparator::Compare() {
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// Cases:
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// * F is external strong, G is external strong:
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// turn G into a thunk to F (1)
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// turn G into a thunk to F
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// * F is external strong, G is external weak:
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// turn G into a thunk to F (1)
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// turn G into a thunk to F
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// * F is external weak, G is external weak:
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// unfoldable
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// * F is external strong, G is internal:
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// address of G taken:
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// turn G into a thunk to F (1)
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// address of G not taken:
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// make G an alias to F (2)
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// turn G into a thunk to F
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// * F is internal, G is external weak
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// address of F is taken:
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// turn G into a thunk to F (1)
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// address of F is not taken:
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// make G an alias of F (2)
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// turn G into a thunk to F
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// * F is internal, G is internal:
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// address of F and G are taken:
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// turn G into a thunk to F (1)
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// address of G is not taken:
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// make G an alias to F (2)
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// turn G into a thunk to F
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//
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// alias requires linkage == (external,local,weak) fallback to creating a thunk
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// external means 'externally visible' linkage != (internal,private)
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// internal means linkage == (internal,private)
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// weak means linkage mayBeOverridable
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// being external implies that the address is taken
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//
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// 1. turn G into a thunk to F
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// 2. make G an alias to F
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enum LinkageCategory {
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ExternalStrong,
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ExternalWeak,
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Internal
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};
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static LinkageCategory categorize(const Function *F) {
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switch (F->getLinkage()) {
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case GlobalValue::InternalLinkage:
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case GlobalValue::PrivateLinkage:
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case GlobalValue::LinkerPrivateLinkage:
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return Internal;
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case GlobalValue::WeakAnyLinkage:
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case GlobalValue::WeakODRLinkage:
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case GlobalValue::ExternalWeakLinkage:
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case GlobalValue::LinkerPrivateWeakLinkage:
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return ExternalWeak;
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case GlobalValue::ExternalLinkage:
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case GlobalValue::AvailableExternallyLinkage:
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case GlobalValue::LinkOnceAnyLinkage:
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case GlobalValue::LinkOnceODRLinkage:
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case GlobalValue::AppendingLinkage:
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case GlobalValue::DLLImportLinkage:
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case GlobalValue::DLLExportLinkage:
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case GlobalValue::CommonLinkage:
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return ExternalStrong;
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}
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llvm_unreachable("Unknown LinkageType.");
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return ExternalWeak;
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}
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/// ThunkGToF - Replace G with a simple tail call to bitcast(F). Also replace
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/// direct uses of G with bitcast(F).
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static void ThunkGToF(Function *F, Function *G) {
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if (!G->mayBeOverridden()) {
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// Redirect direct callers of G to F.
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@ -608,6 +528,13 @@ static void ThunkGToF(Function *F, Function *G) {
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}
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}
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// If G was internal then we may have replaced all uses if G with F. If so,
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// stop here and delete G. There's no need for a thunk.
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if (G->hasLocalLinkage() && G->use_empty()) {
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G->eraseFromParent();
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return;
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}
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Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
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G->getParent());
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BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG);
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@ -643,59 +570,19 @@ static void ThunkGToF(Function *F, Function *G) {
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G->eraseFromParent();
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}
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static void AliasGToF(Function *F, Function *G) {
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// Darwin will trigger llvm_unreachable if asked to codegen an alias.
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return ThunkGToF(F, G);
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#if 0
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if (!G->hasExternalLinkage() && !G->hasLocalLinkage() && !G->hasWeakLinkage())
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return ThunkGToF(F, G);
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GlobalAlias *GA = new GlobalAlias(
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G->getType(), G->getLinkage(), "",
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ConstantExpr::getBitCast(F, G->getType()), G->getParent());
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F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
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GA->takeName(G);
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GA->setVisibility(G->getVisibility());
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G->replaceAllUsesWith(GA);
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G->eraseFromParent();
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#endif
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}
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static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
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Function *F = FnVec[i];
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Function *G = FnVec[j];
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LinkageCategory catF = categorize(F);
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LinkageCategory catG = categorize(G);
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if (catF == ExternalWeak || (catF == Internal && catG == ExternalStrong)) {
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if (F->isWeakForLinker() && !G->isWeakForLinker()) {
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std::swap(FnVec[i], FnVec[j]);
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std::swap(F, G);
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std::swap(catF, catG);
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}
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switch (catF) {
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case ExternalStrong:
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switch (catG) {
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case ExternalStrong:
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case ExternalWeak:
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ThunkGToF(F, G);
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break;
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case Internal:
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if (G->hasAddressTaken())
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ThunkGToF(F, G);
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else
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AliasGToF(F, G);
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break;
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}
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break;
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case ExternalWeak: {
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assert(catG == ExternalWeak);
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if (F->isWeakForLinker()) {
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assert(G->isWeakForLinker());
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// Make them both thunks to the same internal function.
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F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
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Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
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F->getParent());
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H->copyAttributesFrom(F);
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@ -705,37 +592,10 @@ static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
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ThunkGToF(F, G);
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ThunkGToF(F, H);
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F->setAlignment(std::max(G->getAlignment(), H->getAlignment()));
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F->setLinkage(GlobalValue::InternalLinkage);
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} break;
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case Internal:
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switch (catG) {
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case ExternalStrong:
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llvm_unreachable(0);
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// fall-through
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case ExternalWeak:
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if (F->hasAddressTaken())
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ThunkGToF(F, G);
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else
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AliasGToF(F, G);
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break;
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case Internal: {
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bool addrTakenF = F->hasAddressTaken();
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bool addrTakenG = G->hasAddressTaken();
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if (!addrTakenF && addrTakenG) {
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std::swap(FnVec[i], FnVec[j]);
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std::swap(F, G);
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std::swap(addrTakenF, addrTakenG);
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}
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if (addrTakenF && addrTakenG) {
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ThunkGToF(F, G);
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} else {
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assert(!addrTakenG);
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AliasGToF(F, G);
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}
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} break;
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} break;
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ThunkGToF(F, G);
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}
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++NumFunctionsMerged;
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@ -752,7 +612,7 @@ bool MergeFunctions::runOnModule(Module &M) {
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std::map<unsigned long, std::vector<Function *> > FnMap;
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for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
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if (F->isDeclaration())
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if (F->isDeclaration() || F->hasAvailableExternallyLinkage())
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continue;
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FnMap[ProfileFunction(F)].push_back(F);
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