[llvm] Reland: Port Swift's merge function pass to llvm: merging functions that differ in constants (PR #71584)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Tue Nov 7 13:11:59 PST 2023
================
@@ -0,0 +1,1187 @@
+//===--- MergeFunctionsIgnoringConst.cpp - Merge functions ----------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass looks for similar functions that are mergeable and folds them.
+// The implementation is similar to LLVM's MergeFunctions pass. Instead of
+// merging identical functions, it merges functions which only differ by a few
+// constants in certain instructions.
+// This is copied from Swift's implementation.
+//
+// This pass should run after LLVM's MergeFunctions pass, because it works best
+// if there are no _identical_ functions in the module.
+// Note: it would also work for identical functions but could produce more
+// code overhead than the LLVM pass.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/IPO/MergeFunctionsIgnoringConst.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/FoldingSet.h"
+#include "llvm/ADT/Hashing.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/StableHashing.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/ObjCARCUtil.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InlineAsm.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/IR/StructuralHash.h"
+#include "llvm/IR/ValueHandle.h"
+#include "llvm/IR/ValueMap.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Regex.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/Transforms/Utils/FunctionComparatorIgnoringConst.h"
+#include "llvm/Transforms/Utils/MergeFunctionsIgnoringConst.h"
+#include <vector>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "mergefunc-ignoring-const"
+
+STATISTIC(NumFunctionsMergedIgnoringConst, "Number of functions merged");
+STATISTIC(NumThunksWrittenIgnoringConst, "Number of thunks generated");
+
+static cl::opt<unsigned> NumFunctionsIgnoringConstForSanityCheck(
+ "mergefunc-ignoringconst-sanity",
+ cl::desc("How many functions in module could be used for "
+ "MergeFunctionsIgnoringConst pass sanity check. "
+ "'0' disables this check. Works only with '-debug' key."),
+ cl::init(0), cl::Hidden);
+
+static cl::opt<unsigned> IgnoringConstMergeThreshold(
+ "mergefunc-ignoringconst-threshold",
+ cl::desc("Functions larger than the threshold are considered for merging."
+ "'0' disables function merging at all."),
+ cl::init(15), cl::Hidden);
+
+cl::opt<bool> UseLinkOnceODRLinkageMerging(
+ "use-linkonceodr-linkage-merging", cl::init(false), cl::Hidden,
+ cl::desc(
+ "Use LinkeOnceODR linkage to deduplicate the identical merged function "
+ "(default = off)"));
+
+cl::opt<bool> NoInlineForMergedFunction(
+ "no-inline-merged-function", cl::init(false), cl::Hidden,
+ cl::desc("set noinline for merged function (default = off)"));
+
+static cl::opt<bool>
+ CastArrayType("merge-cast-array-type", cl::init(false), cl::Hidden,
+ cl::desc("support for casting array type (default = off)"));
+
+static cl::opt<bool> IgnoreMusttailFunction(
+ "ignore-musttail-function", cl::init(false), cl::Hidden,
+ cl::desc(
+ "ignore functions containing callsites with musttail (default = off)"));
+
+static cl::opt<bool> AlwaysCallThunk(
+ "merge-always-call-thunk", cl::init(false), cl::Hidden,
+ cl::desc(
+ "do not replace callsites and always emit a thunk (default = off)"));
+
+static cl::list<std::string> MergeBlockRegexFilters(
+ "merge-block-regex", cl::Optional,
+ cl::desc("Block functions from merging if they match the given "
+ "regular expression"),
+ cl::ZeroOrMore);
+
+static cl::list<std::string> MergeAllowRegexFilters(
+ "merge-allow-regex", cl::Optional,
+ cl::desc("Allow functions from merging if they match the given "
+ "regular expression"),
+ cl::ZeroOrMore);
+
+namespace {
+
+/// MergeFuncIgnoringConst finds functions which only differ by constants in
+/// certain instructions, e.g. resulting from specialized functions of layout
+/// compatible types.
+/// Such functions are merged by replacing the differing constants by a
+/// parameter. The original functions are replaced by thunks which call the
+/// merged function with the specific argument constants.
+///
+class MergeFuncIgnoringConstImpl {
+public:
+ MergeFuncIgnoringConstImpl(std::string Suffix)
+ : FnTree(FunctionNodeCmp(&GlobalNumbers)), MergeFuncSuffix(Suffix) {}
+
+ bool runImpl(Module &M);
+
+private:
+ struct FunctionEntry;
+
+ /// Describes the set of functions which are considered as "equivalent" (i.e.
+ /// only differing by some constants).
+ struct EquivalenceClass {
+ /// The single-linked list of all functions which are a member of this
+ /// equivalence class.
+ FunctionEntry *First;
+
+ /// A very cheap hash, used to early exit if functions do not match.
+ IRHash Hash;
+
+ public:
+ // Note the hash is recalculated potentially multiple times, but it is
+ // cheap.
+ EquivalenceClass(FunctionEntry *First)
+ : First(First), Hash(StructuralHash(*First->F)) {
+ assert(!First->Next);
+ }
+ };
+
+ /// The function comparison operator is provided here so that FunctionNodes do
+ /// not need to become larger with another pointer.
+ class FunctionNodeCmp {
+ GlobalNumberState *GlobalNumbers;
+
+ public:
+ FunctionNodeCmp(GlobalNumberState *GN) : GlobalNumbers(GN) {}
+ bool operator()(const EquivalenceClass &LHS,
+ const EquivalenceClass &RHS) const {
+ // Order first by hashes, then full function comparison.
+ if (LHS.Hash != RHS.Hash)
+ return LHS.Hash < RHS.Hash;
+ FunctionComparatorIgnoringConst FCmp(LHS.First->F, RHS.First->F,
+ GlobalNumbers);
+ return FCmp.compareIgnoringConsts() == -1;
+ }
+ };
+ using FnTreeType = std::set<EquivalenceClass, FunctionNodeCmp>;
+
+ ///
+ struct FunctionEntry {
+ FunctionEntry(Function *F, FnTreeType::iterator I)
+ : F(F), Next(nullptr), NumUnhandledCallees(0), TreeIter(I),
+ IsMerged(false) {}
+
+ /// Back-link to the function.
+ AssertingVH<Function> F;
+
+ /// The next function in its equivalence class.
+ FunctionEntry *Next;
+
+ /// The number of not-yet merged callees. Used to process the merging in
+ /// bottom-up call order.
+ /// This is only valid in the first entry of an equivalence class. The
+ /// counts of all functions in an equivalence class are accumulated in the
+ /// first entry.
+ int NumUnhandledCallees;
+
+ /// The iterator of the function's equivalence class in the FnTree.
+ /// It's FnTree.end() if the function is not in an equivalence class.
+ FnTreeType::iterator TreeIter;
+
+ /// True if this function is already a thunk, calling the merged function.
+ bool IsMerged;
+ };
+
+ /// Describes an operator of a specific instruction.
+ struct OpLocation {
+ Instruction *I;
+ unsigned OpIndex;
+ };
+
+ /// Information for a function. Used during merging.
+ struct FunctionInfo {
+
+ FunctionInfo(Function *F)
+ : F(F), CurrentInst(nullptr), NumParamsNeeded(0) {}
+
+ void init() {
+ CurrentInst = &*F->begin()->begin();
+ NumParamsNeeded = 0;
+ }
+
+ /// Advances the current instruction to the next instruction.
+ void nextInst() {
+ assert(CurrentInst);
+ if (CurrentInst->isTerminator()) {
+ auto BlockIter = std::next(CurrentInst->getParent()->getIterator());
+ if (BlockIter == F->end()) {
+ CurrentInst = nullptr;
+ return;
+ }
+ CurrentInst = &*BlockIter->begin();
+ return;
+ }
+ CurrentInst = &*std::next(CurrentInst->getIterator());
+ }
+
+ Function *F;
+
+ /// The current instruction while iterating over all instructions.
+ Instruction *CurrentInst;
+
+ /// Roughly the number of parameters needed if this function would be
+ /// merged with the first function of the equivalence class.
+ int NumParamsNeeded;
+ };
+
+ using FunctionInfos = SmallVector<FunctionInfo, 8>;
+
+ /// Describes a parameter which we create to parameterize the merged function.
+ struct ParamInfo {
+ /// The value of the parameter for all the functions in the equivalence
+ /// class.
+ SmallVector<Constant *, 8> Values;
+
+ /// All uses of the parameter in the merged function.
+ SmallVector<OpLocation, 16> Uses;
+
+ /// Checks if this parameter can be used to describe an operand in all
+ /// functions of the equivalence class. Returns true if all values match
+ /// the specific instruction operands in all functions.
+ bool matches(const FunctionInfos &FInfos, unsigned OpIdx) const {
+ unsigned NumFuncs = FInfos.size();
+ assert(Values.size() == NumFuncs);
+ for (unsigned Idx = 0; Idx < NumFuncs; ++Idx) {
+ const FunctionInfo &FI = FInfos[Idx];
+ Constant *C = cast<Constant>(FI.CurrentInst->getOperand(OpIdx));
+ if (Values[Idx] != C)
+ return false;
+ }
+ return true;
+ }
+ };
+
+ using ParamInfos = SmallVector<ParamInfo, 16>;
+
+ Module *CurrentModule = nullptr;
+
+ GlobalNumberState GlobalNumbers;
+
+ /// A work queue of functions that may have been modified and should be
+ /// analyzed again.
+ std::vector<WeakTrackingVH> Deferred;
+
+ /// The set of all distinct functions. Use the insert() and remove() methods
+ /// to modify it. The map allows efficient lookup and deferring of Functions.
+ FnTreeType FnTree;
+
+ ValueMap<Function *, FunctionEntry *> FuncEntries;
+
+ std::string MergeFuncSuffix = ".Tm";
+
+ FunctionEntry *getEntry(Function *F) const { return FuncEntries.lookup(F); }
+
+ bool isInEquivalenceClass(FunctionEntry *FE) const {
+ if (FE->TreeIter != FnTree.end()) {
+ return true;
+ }
+ assert(!FE->Next);
+ assert(FE->NumUnhandledCallees == 0);
+ return false;
+ }
+
+ /// Checks the rules of order relation introduced among functions set.
+ /// Returns true, if sanity check has been passed, and false if failed.
+ bool doSanityCheck(std::vector<WeakTrackingVH> &Worklist);
+
+ /// Updates the NumUnhandledCallees of all user functions of the equivalence
+ /// class containing \p FE by \p Delta.
+ void updateUnhandledCalleeCount(FunctionEntry *FE, int Delta);
+
+ bool tryMergeEquivalenceClass(FunctionEntry *FirstInClass);
+
+ FunctionInfo removeFuncWithMostParams(FunctionInfos &FInfos);
+
+ bool deriveParams(ParamInfos &Params, FunctionInfos &FInfos,
+ unsigned maxParams);
+
+ bool numOperandsDiffer(FunctionInfos &FInfos);
+
+ bool constsDiffer(const FunctionInfos &FInfos, unsigned OpIdx);
+
+ bool tryMapToParameter(FunctionInfos &FInfos, unsigned OpIdx,
+ ParamInfos &Params, unsigned maxParams);
+
+ void mergeWithParams(const FunctionInfos &FInfos, ParamInfos &Params);
+ static void dumpMergeInfo(const FunctionInfos &FInfos, unsigned);
+
+ void removeEquivalenceClassFromTree(FunctionEntry *FE);
+
+ void writeThunk(Function *ToFunc, Function *Thunk, const ParamInfos &Params,
+ unsigned FuncIdx);
+
+ /// Returns the value of function \p FuncIdx.
+ Constant *getFunctionValue(const ParamInfo &PI, unsigned FuncIdx) {
+ Constant *value = PI.Values[FuncIdx];
+ return value;
+ }
+
+ /// Replace all direct calls of Old with calls of New. Will bitcast New if
+ /// necessary to make types match.
+ bool replaceDirectCallers(Function *Old, Function *New,
+ const ParamInfos &Params, unsigned FuncIdx);
+};
+
+} // end anonymous namespace
+
+bool MergeFuncIgnoringConstImpl::doSanityCheck(
+ std::vector<WeakTrackingVH> &Worklist) {
+ if (const unsigned Max = NumFunctionsIgnoringConstForSanityCheck) {
+ unsigned TripleNumber = 0;
+ bool Valid = true;
+
+ dbgs() << "MERGEFUNC-SANITY: Started for first " << Max << " functions.\n";
+
+ unsigned i = 0;
+ for (std::vector<WeakTrackingVH>::iterator I = Worklist.begin(),
+ E = Worklist.end();
+ I != E && i < Max; ++I, ++i) {
+ unsigned j = i;
+ for (std::vector<WeakTrackingVH>::iterator J = I; J != E && j < Max;
+ ++J, ++j) {
+ Function *F1 = cast<Function>(*I);
+ Function *F2 = cast<Function>(*J);
+ int Res1 = FunctionComparatorIgnoringConst(F1, F2, &GlobalNumbers)
+ .compareIgnoringConsts();
+ int Res2 = FunctionComparatorIgnoringConst(F2, F1, &GlobalNumbers)
+ .compareIgnoringConsts();
+
+ // If F1 <= F2, then F2 >= F1, otherwise report failure.
+ if (Res1 != -Res2) {
+ dbgs() << "MERGEFUNC-SANITY: Non-symmetric; triple: " << TripleNumber
+ << "\n";
+ LLVM_DEBUG(F1->dump());
+ LLVM_DEBUG(F2->dump());
+ Valid = false;
+ }
+
+ if (Res1 == 0)
+ continue;
+
+ unsigned k = j;
+ for (std::vector<WeakTrackingVH>::iterator K = J; K != E && k < Max;
+ ++k, ++K, ++TripleNumber) {
+ if (K == J)
+ continue;
+
+ Function *F3 = cast<Function>(*K);
+ int Res3 = FunctionComparatorIgnoringConst(F1, F3, &GlobalNumbers)
+ .compareIgnoringConsts();
+ int Res4 = FunctionComparatorIgnoringConst(F2, F3, &GlobalNumbers)
+ .compareIgnoringConsts();
+
+ bool Transitive = true;
+
+ if (Res1 != 0 && Res1 == Res4) {
+ // F1 > F2, F2 > F3 => F1 > F3
+ Transitive = Res3 == Res1;
+ } else if (Res3 != 0 && Res3 == -Res4) {
+ // F1 > F3, F3 > F2 => F1 > F2
+ Transitive = Res3 == Res1;
+ } else if (Res4 != 0 && -Res3 == Res4) {
+ // F2 > F3, F3 > F1 => F2 > F1
+ Transitive = Res4 == -Res1;
+ }
+
+ if (!Transitive) {
+ dbgs() << "MERGEFUNC-SANITY: Non-transitive; triple: "
+ << TripleNumber << "\n";
+ dbgs() << "Res1, Res3, Res4: " << Res1 << ", " << Res3 << ", "
+ << Res4 << "\n";
+ LLVM_DEBUG(F1->dump());
+ LLVM_DEBUG(F2->dump());
+ LLVM_DEBUG(F3->dump());
+ Valid = false;
+ }
+ }
+ }
+ }
+
+ dbgs() << "MERGEFUNC-SANITY: " << (Valid ? "Passed." : "Failed.") << "\n";
+ return Valid;
+ }
+ return true;
+}
+
+/// Returns true if functions containing calls to \p F may be merged together.
+static bool mayMergeCallsToFunction(Function &F) {
+ StringRef Name = F.getName();
+
+ // Calls to dtrace probes must generate unique patchpoints.
+ if (Name.startswith("__dtrace"))
+ return false;
+
+ return true;
+}
+
+/// Returns the benefit, which is approximately the size of the function.
+/// Return 0, if the function should not be merged.
+static unsigned getBenefit(Function *F) {
+ unsigned Benefit = 0;
+
+ // We don't want to merge very small functions, because the overhead of
+ // adding creating thunks and/or adding parameters to the call sites
+ // outweighs the benefit.
+ for (BasicBlock &BB : *F) {
+ for (Instruction &I : BB) {
+ if (CallBase *CB = dyn_cast<CallBase>(&I)) {
+ Function *Callee = CB->getCalledFunction();
+ if (Callee && !mayMergeCallsToFunction(*Callee))
+ return 0;
+ if (!Callee || !Callee->isIntrinsic()) {
+ Benefit += 5;
+ continue;
+ }
+ }
+ Benefit += 1;
+ }
+ }
+ return Benefit;
+}
+
+/// Returns true if function \p F is eligible for merging.
+bool isEligibleFunction(Function *F) {
+ if (F->isDeclaration())
+ return false;
+
+ if (F->hasFnAttribute(Attribute::NoMerge))
+ return false;
+
+ if (F->hasAvailableExternallyLinkage()) {
+ return false;
+ }
+
+ if (F->getFunctionType()->isVarArg()) {
+ return false;
+ }
+
+ // Check against blocklist.
+ if (!MergeBlockRegexFilters.empty()) {
+ StringRef FuncName = F->getName();
+ for (const auto &tRegex : MergeBlockRegexFilters)
+ if (Regex(tRegex).match(FuncName)) {
+ return false;
+ }
+ }
+ // Check against allowlist
+ if (!MergeAllowRegexFilters.empty()) {
+ StringRef FuncName = F->getName();
+ bool found = false;
+ for (const auto &tRegex : MergeAllowRegexFilters)
+ if (Regex(tRegex).match(FuncName)) {
+ found = true;
+ break;
+ }
+ if (!found)
+ return false;
+ }
+
+ if (F->getCallingConv() == CallingConv::SwiftTail)
+ return false;
+
+ // if function contains callsites with musttail, if we merge
+ // it, the merged function will have the musttail callsite, but
+ // the number of parameters can change, thus the parameter count
+ // of the callsite will mismatch with the function itself.
+ if (IgnoreMusttailFunction) {
+ for (const BasicBlock &BB : *F) {
+ for (const Instruction &I : BB) {
+ const auto *CB = dyn_cast<CallBase>(&I);
+ if (CB && CB->isMustTailCall())
+ return false;
+ }
+ }
+ }
+
+ unsigned Benefit = getBenefit(F);
+ if (Benefit < IgnoringConstMergeThreshold) {
+ return false;
+ }
+
+ return true;
+}
+
+bool MergeFuncIgnoringConstImpl::runImpl(Module &M) {
+ if (IgnoringConstMergeThreshold == 0)
+ return false;
+
+ CurrentModule = &M;
+
+ // TODO: fix pointer authentication
+
+ bool Changed = false;
+
+ // All functions in the module, ordered by hash. Functions with a unique
+ // hash value are easily eliminated.
+ std::vector<std::pair<IRHash, Function *>> HashedFuncs;
+
+ for (Function &Func : M) {
+ if (isEligibleFunction(&Func)) {
+ HashedFuncs.push_back({StructuralHash(Func), &Func});
+ }
+ }
+
+ std::stable_sort(
+ HashedFuncs.begin(), HashedFuncs.end(),
+ [](const std::pair<IRHash, Function *> &a,
+ const std::pair<IRHash, Function *> &b) { return a.first < b.first; });
+
+ std::vector<FunctionEntry> FuncEntryStorage;
+ FuncEntryStorage.reserve(HashedFuncs.size());
+
+ auto S = HashedFuncs.begin();
+ for (auto I = HashedFuncs.begin(), IE = HashedFuncs.end(); I != IE; ++I) {
+
+ Function *F = I->second;
+ FuncEntryStorage.push_back(FunctionEntry(F, FnTree.end()));
+ FunctionEntry &FE = FuncEntryStorage.back();
+ FuncEntries[F] = &FE;
+
+ // If the hash value matches the previous value or the next one, we must
+ // consider merging it. Otherwise it is dropped and never considered again.
+ if ((I != S && std::prev(I)->first == I->first) ||
+ (std::next(I) != IE && std::next(I)->first == I->first)) {
+ Deferred.push_back(WeakTrackingVH(F));
+ }
+ }
+
+ do {
+ std::vector<WeakTrackingVH> Worklist;
+ Deferred.swap(Worklist);
+
+ LLVM_DEBUG(dbgs() << "======\nbuild tree: worklist-size=" << Worklist.size()
+ << '\n');
+ LLVM_DEBUG(doSanityCheck(Worklist));
+
+ SmallVector<FunctionEntry *, 8> FuncsToMerge;
+
+ // Insert all candidates into the Worklist.
+ for (WeakTrackingVH &I : Worklist) {
+ if (!I)
+ continue;
+ Function *F = cast<Function>(I);
+ FunctionEntry *FE = getEntry(F);
+ assert(!isInEquivalenceClass(FE));
+
+ std::pair<FnTreeType::iterator, bool> Result = FnTree.insert(FE);
+
+ FE->TreeIter = Result.first;
+ const EquivalenceClass &Eq = *Result.first;
+
+ if (Result.second) {
+ assert(Eq.First == FE);
+ LLVM_DEBUG(dbgs() << " new in tree: " << F->getName() << '\n');
+ } else {
+ assert(Eq.First != FE);
+ LLVM_DEBUG(dbgs() << " add to existing: " << F->getName() << '\n');
+ // Add the function to the existing equivalence class.
+ FE->Next = Eq.First->Next;
+ Eq.First->Next = FE;
+ // Schedule for merging if the function's equivalence class reaches the
+ // size of 2.
+ if (!FE->Next)
+ FuncsToMerge.push_back(Eq.First);
+ }
+ }
+ LLVM_DEBUG(dbgs() << "merge functions: tree-size=" << FnTree.size()
+ << '\n');
+
+ // Figure out the leaf functions. We want to do the merging in bottom-up
+ // call order. This ensures that we don't parameterize on callee function
+ // names if we don't have to (because the callee may be merged).
+ // Note that "leaf functions" refer to the sub-call-graph of functions which
+ // are in the FnTree.
+ for (FunctionEntry *ToMerge : FuncsToMerge) {
+ assert(isInEquivalenceClass(ToMerge));
+ updateUnhandledCalleeCount(ToMerge, 1);
+ }
+
+ // Check if there are any leaf functions at all.
+ bool LeafFound = false;
+ for (FunctionEntry *ToMerge : FuncsToMerge) {
+ if (ToMerge->NumUnhandledCallees == 0)
+ LeafFound = true;
+ }
+ for (FunctionEntry *ToMerge : FuncsToMerge) {
+ if (isInEquivalenceClass(ToMerge)) {
+ // Only merge leaf functions (or all functions if all functions are in
+ // a call cycle).
+ if (ToMerge->NumUnhandledCallees == 0 || !LeafFound) {
+ updateUnhandledCalleeCount(ToMerge, -1);
+ Changed |= tryMergeEquivalenceClass(ToMerge);
+ } else {
+ // Non-leaf functions (i.e. functions in a call cycle) may become
+ // leaf functions in the next iteration.
+ removeEquivalenceClassFromTree(ToMerge);
+ }
+ }
+ }
+ } while (!Deferred.empty());
+
+ FnTree.clear();
+ GlobalNumbers.clear();
+ FuncEntries.clear();
+
+ return Changed;
+}
+
+void MergeFuncIgnoringConstImpl::updateUnhandledCalleeCount(FunctionEntry *FE,
+ int Delta) {
+ // Iterate over all functions of FE's equivalence class.
+ do {
+ for (Use &U : FE->F->uses()) {
+ if (auto *I = dyn_cast<Instruction>(U.getUser())) {
+ FunctionEntry *CallerFE = getEntry(I->getFunction());
+ if (CallerFE && CallerFE->TreeIter != FnTree.end()) {
+ // Accumulate the count in the first entry of the equivalence class.
+ FunctionEntry *Head = CallerFE->TreeIter->First;
+ Head->NumUnhandledCallees += Delta;
+ }
+ }
+ }
+ FE = FE->Next;
+ } while (FE);
+}
+
+bool MergeFuncIgnoringConstImpl::tryMergeEquivalenceClass(
+ FunctionEntry *FirstInClass) {
+ // Build the FInfos vector from all functions in the equivalence class.
+ FunctionInfos FInfos;
+ FunctionEntry *FE = FirstInClass;
+ do {
+ FInfos.push_back(FunctionInfo(FE->F));
+ FE->IsMerged = true;
+ FE = FE->Next;
+ } while (FE);
+ assert(FInfos.size() >= 2);
+
+ // Merged or not: in any case we remove the equivalence class from the FnTree.
+ removeEquivalenceClassFromTree(FirstInClass);
+
+ // Contains functions which differ too much from the first function (i.e.
+ // would need too many parameters).
+ FunctionInfos Removed;
+
+ bool Changed = false;
+ int Try = 0;
+
+ unsigned Benefit = getBenefit(FirstInClass->F);
+
+ // The bigger the function, the more parameters are allowed.
+ unsigned maxParams = std::max(4u, Benefit / 100);
+
+ // We need multiple tries if there are some functions in FInfos which differ
+ // too much from the first function in FInfos. But we limit the number of
+ // tries to a small number, because this is quadratic.
+ while (FInfos.size() >= 2 && Try++ < 4) {
+ ParamInfos Params;
+ bool Merged = deriveParams(Params, FInfos, maxParams);
+ if (Merged) {
+ mergeWithParams(FInfos, Params);
+ Changed = true;
+ } else {
+ // We ran out of parameters. Remove the function from the set which
+ // differs most from the first function.
+ Removed.push_back(removeFuncWithMostParams(FInfos));
+ }
+ if (Merged || FInfos.size() < 2) {
+ // Try again with the functions which were removed from the original set.
+ FInfos.swap(Removed);
+ Removed.clear();
+ }
+ }
+ return Changed;
+}
+
+/// Remove the function from \p FInfos which needs the most parameters. Add the
+/// removed function to
+MergeFuncIgnoringConstImpl::FunctionInfo
+MergeFuncIgnoringConstImpl::removeFuncWithMostParams(FunctionInfos &FInfos) {
+ FunctionInfos::iterator MaxIter = FInfos.end();
+ for (auto Iter = FInfos.begin(), End = FInfos.end(); Iter != End; ++Iter) {
+ if (MaxIter == FInfos.end() ||
+ Iter->NumParamsNeeded > MaxIter->NumParamsNeeded) {
+ MaxIter = Iter;
+ }
+ }
+ FunctionInfo Removed = *MaxIter;
+ FInfos.erase(MaxIter);
+ return Removed;
+}
+
+/// Finds the set of parameters which are required to merge the functions in
+/// \p FInfos.
+/// Returns true on success, i.e. the functions in \p FInfos can be merged with
+/// the parameters returned in \p Params.
+bool MergeFuncIgnoringConstImpl::deriveParams(ParamInfos &Params,
+ FunctionInfos &FInfos,
+ unsigned maxParams) {
+ for (FunctionInfo &FI : FInfos)
+ FI.init();
+
+ FunctionInfo &FirstFI = FInfos.front();
+
+ // Iterate over all instructions synchronously in all functions.
+ do {
+ if (isEligibleInstrunctionForConstantSharing(FirstFI.CurrentInst)) {
+
+ // Here we handle a rare corner case which needs to be explained:
+ // Usually the number of operands match, because otherwise the functions
+ // in FInfos would not be in the same equivalence class. There is only one
+ // exception to that: If the current instruction is a call to a function,
+ // which was merged in the previous iteration (in
+ // tryMergeEquivalenceClass) then the call could be replaced and has more
+ // arguments than the original call.
+ if (numOperandsDiffer(FInfos)) {
+ assert(isa<CallInst>(FirstFI.CurrentInst) &&
+ "only calls are expected to differ in number of operands");
+ return false;
+ }
+
+ for (unsigned OpIdx = 0, NumOps = FirstFI.CurrentInst->getNumOperands();
+ OpIdx != NumOps; ++OpIdx) {
+
+ if (constsDiffer(FInfos, OpIdx)) {
+ // This instruction has operands which differ in at least some
+ // functions. So we need to parameterize it.
+ if (!tryMapToParameter(FInfos, OpIdx, Params, maxParams)) {
+ // We ran out of parameters.
+ return false;
+ }
+ }
+ }
+ }
+ // Go to the next instruction in all functions.
+ for (FunctionInfo &FI : FInfos)
+ FI.nextInst();
+ } while (FirstFI.CurrentInst);
+
+ return true;
+}
+
+/// Returns true if the number of operands of the current instruction differs.
+bool MergeFuncIgnoringConstImpl::numOperandsDiffer(FunctionInfos &FInfos) {
+ unsigned numOps = FInfos[0].CurrentInst->getNumOperands();
+ for (const FunctionInfo &FI : ArrayRef<FunctionInfo>(FInfos).drop_front(1)) {
+ if (FI.CurrentInst->getNumOperands() != numOps)
+ return true;
+ }
+ return false;
+}
+
+/// Returns true if the \p OpIdx's constant operand in the current instruction
+/// does differ in any of the functions in \p FInfos.
+bool MergeFuncIgnoringConstImpl::constsDiffer(const FunctionInfos &FInfos,
+ unsigned OpIdx) {
+ Constant *CommonConst = nullptr;
+
+ for (const FunctionInfo &FI : FInfos) {
+ Value *Op = FI.CurrentInst->getOperand(OpIdx);
+ if (auto *C = dyn_cast<Constant>(Op)) {
+ if (!CommonConst) {
+ CommonConst = C;
+ } else if (C != CommonConst) {
+ return true;
+ }
+ }
+ }
+ return false;
+}
+
+/// Create a new parameter for differing operands or try to reuse an existing
+/// parameter.
+/// Returns true if a parameter could be created or found without exceeding the
+/// maximum number of parameters.
+bool MergeFuncIgnoringConstImpl::tryMapToParameter(FunctionInfos &FInfos,
+ unsigned OpIdx,
+ ParamInfos &Params,
+ unsigned maxParams) {
+ ParamInfo *Matching = nullptr;
+ // Try to find an existing parameter which exactly matches the differing
+ // operands of the current instruction.
+ for (ParamInfo &PI : Params) {
+ if (PI.matches(FInfos, OpIdx)) {
+ Matching = &PI;
+ break;
+ }
+ }
+ if (!Matching) {
+ // We need a new parameter.
+ // Check if we are within the limit.
+ if (Params.size() >= maxParams)
+ return false;
+
+ Params.resize(Params.size() + 1);
+ Matching = &Params.back();
+ // Store the constant values into the new parameter.
+ Constant *FirstC = cast<Constant>(FInfos[0].CurrentInst->getOperand(OpIdx));
+ for (FunctionInfo &FI : FInfos) {
+ Constant *C = cast<Constant>(FI.CurrentInst->getOperand(OpIdx));
+ Matching->Values.push_back(C);
+ if (C != FirstC)
+ FI.NumParamsNeeded += 1;
+ }
+ }
+ /// Remember where the parameter is needed when we build our merged function.
+ Matching->Uses.push_back({FInfos[0].CurrentInst, OpIdx});
+ return true;
+}
+
+void MergeFuncIgnoringConstImpl::dumpMergeInfo(const FunctionInfos &FInfos,
+ unsigned paramSize) {
+ std::set<IRHash> oHashes;
+ std::vector<std::string> funcLocs;
+ Function *OrigFunc = nullptr;
+ for (const auto &FInfo : FInfos) {
+ OrigFunc = FInfo.F;
+
+ IRHash origHash = StructuralHash(*OrigFunc);
+ oHashes.insert(origHash);
+
+ // Print debug location.
+ std::string Result;
+ raw_string_ostream DbgLocOS(Result);
+ if (DISubprogram *DIS = OrigFunc->getSubprogram()) {
+ DebugLoc FuncDbgLoc =
+ DILocation::get(DIS->getContext(), DIS->getScopeLine(), 0, DIS);
+ FuncDbgLoc.print(DbgLocOS);
+ DbgLocOS.flush();
+ }
+ std::string singleLine =
+ "# functionLoc " +
+ std::to_string(GlobalValue::getGUID(OrigFunc->getName())) + " " +
+ Result + " " + std::string(OrigFunc->getName()) + "\n";
+ funcLocs.push_back(singleLine);
+ }
+}
+
+/// Merge all functions in \p FInfos by creating thunks which call the single
+/// merged function with additional parameters.
+void MergeFuncIgnoringConstImpl::mergeWithParams(const FunctionInfos &FInfos,
+ ParamInfos &Params) {
+ // We reuse the body of the first function for the new merged function.
+ Function *FirstF = FInfos.front().F;
+
+ // Build the type for the merged function. This will be the type of the
+ // original function (FirstF) but with the additional parameter which are
+ // needed to parameterize the merged function.
+ FunctionType *OrigTy = FirstF->getFunctionType();
+ SmallVector<Type *, 8> ParamTypes(OrigTy->param_begin(), OrigTy->param_end());
+
+ for (const ParamInfo &PI : Params) {
+ ParamTypes.push_back(PI.Values[0]->getType());
+ }
+
+ FunctionType *funcType =
+ FunctionType::get(OrigTy->getReturnType(), ParamTypes, false);
+
+ // Create the new function.
+ Function *NewFunction = Function::Create(funcType, FirstF->getLinkage(),
+ FirstF->getName() + MergeFuncSuffix);
+ if (auto *SP = FirstF->getSubprogram())
+ NewFunction->setSubprogram(SP);
+ NewFunction->copyAttributesFrom(FirstF);
+ // NOTE: this function is not externally available, do ensure that we reset
+ // the DLL storage
+ NewFunction->setDLLStorageClass(GlobalValue::DefaultStorageClass);
+ if (UseLinkOnceODRLinkageMerging)
+ NewFunction->setLinkage(GlobalValue::LinkOnceODRLinkage);
+ else
+ NewFunction->setLinkage(GlobalValue::InternalLinkage);
+ if (NoInlineForMergedFunction)
+ NewFunction->addFnAttr(Attribute::NoInline);
+
+ // Insert the new function after the last function in the equivalence class.
+ FirstF->getParent()->getFunctionList().insert(
+ std::next(FInfos[1].F->getIterator()), NewFunction);
+
+ LLVM_DEBUG(dbgs() << " Merge into " << NewFunction->getName() << '\n');
+
+ // Move the body of FirstF into the NewFunction.
+ NewFunction->splice(NewFunction->begin(), FirstF);
+
+ auto NewArgIter = NewFunction->arg_begin();
+ for (Argument &OrigArg : FirstF->args()) {
+ Argument &NewArg = *NewArgIter++;
+ OrigArg.replaceAllUsesWith(&NewArg);
+ }
+ unsigned numOrigArgs = FirstF->arg_size();
+
+ SmallPtrSet<Function *, 8> SelfReferencingFunctions;
+
+ // Replace all differing operands with a parameter.
+ for (unsigned paramIdx = 0; paramIdx < Params.size(); ++paramIdx) {
+ const ParamInfo &PI = Params[paramIdx];
+ Argument *NewArg = NewFunction->getArg(numOrigArgs + paramIdx);
+
+ for (const OpLocation &OL : PI.Uses) {
+ OL.I->setOperand(OL.OpIndex, NewArg);
+ }
+ // Collect all functions which are referenced by any parameter.
+ for (Value *V : PI.Values) {
+ if (auto *F = dyn_cast<Function>(V))
+ SelfReferencingFunctions.insert(F);
+ }
+ }
+
+ for (unsigned FIdx = 0, NumFuncs = FInfos.size(); FIdx < NumFuncs; ++FIdx) {
+ Function *OrigFunc = FInfos[FIdx].F;
+ // Don't try to replace all callers of functions which are used as
+ // parameters because we must not delete such functions.
+ if (SelfReferencingFunctions.count(OrigFunc) == 0 &&
+ replaceDirectCallers(OrigFunc, NewFunction, Params, FIdx)) {
+ // We could replace all uses (and the function is not externally visible),
+ // so we can delete the original function.
+ auto Iter = FuncEntries.find(OrigFunc);
+ assert(Iter != FuncEntries.end());
+ assert(!isInEquivalenceClass(&*Iter->second));
+ Iter->second->F = nullptr;
+ FuncEntries.erase(Iter);
+ LLVM_DEBUG(dbgs() << " Erase " << OrigFunc->getName() << '\n');
+ OrigFunc->eraseFromParent();
+ } else {
+ // Otherwise we need a thunk which calls the merged function.
+ writeThunk(NewFunction, OrigFunc, Params, FIdx);
+ }
+ ++NumFunctionsMergedIgnoringConst;
+ }
+}
+
+/// Remove all functions of \p FE's equivalence class from FnTree. Add them to
+/// Deferred so that we'll look at them in the next round.
+void MergeFuncIgnoringConstImpl::removeEquivalenceClassFromTree(
+ FunctionEntry *FE) {
+ if (!isInEquivalenceClass(FE))
+ return;
+
+ FnTreeType::iterator Iter = FE->TreeIter;
+ FunctionEntry *Unlink = Iter->First;
+ Unlink->NumUnhandledCallees = 0;
+ while (Unlink) {
+ LLVM_DEBUG(dbgs() << " remove from tree: " << Unlink->F->getName()
+ << '\n');
+ if (!Unlink->IsMerged)
+ Deferred.emplace_back(Unlink->F);
+ Unlink->TreeIter = FnTree.end();
+ assert(Unlink->NumUnhandledCallees == 0);
+ FunctionEntry *NextEntry = Unlink->Next;
+ Unlink->Next = nullptr;
+ Unlink = NextEntry;
+ }
+ FnTree.erase(Iter);
+}
+
+// Helper for writeThunk,
+// Selects proper bitcast operation,
+// but a bit simpler then CastInst::getCastOpcode.
+Value *createCast(IRBuilder<> &Builder, Value *V, Type *DestTy) {
+ Type *SrcTy = V->getType();
+ if (SrcTy->isStructTy()) {
+ assert(DestTy->isStructTy());
+ assert(SrcTy->getStructNumElements() == DestTy->getStructNumElements());
+ Value *Result = UndefValue::get(DestTy);
+ for (unsigned int I = 0, E = SrcTy->getStructNumElements(); I < E; ++I) {
+ Value *Element =
+ createCast(Builder, Builder.CreateExtractValue(V, ArrayRef(I)),
+ DestTy->getStructElementType(I));
+
+ Result = Builder.CreateInsertValue(Result, Element, ArrayRef(I));
+ }
+ return Result;
+ }
+ assert(!DestTy->isStructTy());
+ if (CastArrayType) {
+ if (auto *SrcAT = dyn_cast<ArrayType>(SrcTy)) {
+ auto *DestAT = dyn_cast<ArrayType>(DestTy);
+ assert(DestAT);
+ assert(SrcAT->getNumElements() == DestAT->getNumElements());
+ Value *Result = UndefValue::get(DestTy);
+ for (unsigned int I = 0, E = SrcAT->getNumElements(); I < E; ++I) {
+ Value *Element =
+ createCast(Builder, Builder.CreateExtractValue(V, ArrayRef(I)),
+ DestAT->getElementType());
+
+ Result = Builder.CreateInsertValue(Result, Element, ArrayRef(I));
+ }
+ return Result;
+ }
+ assert(!DestTy->isArrayTy());
+ }
+ if (SrcTy->isIntegerTy() && DestTy->isPointerTy())
+ return Builder.CreateIntToPtr(V, DestTy);
+ else if (SrcTy->isPointerTy() && DestTy->isIntegerTy())
+ return Builder.CreatePtrToInt(V, DestTy);
+ else
+ return Builder.CreateBitCast(V, DestTy);
+}
+
+/// Replace \p Thunk with a simple tail call to \p ToFunc. Also add parameters
+/// to the call to \p ToFunc, which are defined by the FuncIdx's value in
+/// \p Params.
+void MergeFuncIgnoringConstImpl::writeThunk(Function *ToFunc, Function *Thunk,
+ const ParamInfos &Params,
+ unsigned FuncIdx) {
+ // Delete the existing content of Thunk.
+ Thunk->dropAllReferences();
+
+ BasicBlock *BB = BasicBlock::Create(Thunk->getContext(), "", Thunk);
+ IRBuilder<> Builder(BB);
+
+ SmallVector<Value *, 16> Args;
+ unsigned ParamIdx = 0;
+ FunctionType *ToFuncTy = ToFunc->getFunctionType();
+
+ // Add arguments which are passed through Thunk.
+ for (Argument &AI : Thunk->args()) {
+ Args.push_back(createCast(Builder, &AI, ToFuncTy->getParamType(ParamIdx)));
+ ++ParamIdx;
+ }
+ // Add new arguments defined by Params.
+ for (const ParamInfo &PI : Params) {
+ assert(ParamIdx < ToFuncTy->getNumParams());
+ Constant *param = getFunctionValue(PI, FuncIdx);
+ Args.push_back(
+ createCast(Builder, param, ToFuncTy->getParamType(ParamIdx)));
+ ++ParamIdx;
+ }
+
+ CallInst *CI = Builder.CreateCall(ToFunc, Args);
+ bool isSwiftTailCall = ToFunc->getCallingConv() == CallingConv::SwiftTail &&
+ Thunk->getCallingConv() == CallingConv::SwiftTail;
+ CI->setTailCallKind(isSwiftTailCall ? CallInst::TCK_MustTail
+ : CallInst::TCK_Tail);
+ CI->setCallingConv(ToFunc->getCallingConv());
+ CI->setAttributes(ToFunc->getAttributes());
+ if (Thunk->getReturnType()->isVoidTy()) {
+ Builder.CreateRetVoid();
+ } else {
+ Builder.CreateRet(createCast(Builder, CI, Thunk->getReturnType()));
+ }
+
+ LLVM_DEBUG(dbgs() << " writeThunk: " << Thunk->getName() << '\n');
+ ++NumThunksWrittenIgnoringConst;
+}
+
+static AttributeList
+fixUpTypesInByValAndStructRetAttributes(FunctionType *fnType,
+ AttributeList attrList) {
+ // supportsTypedPointers always returns false now.
+ return attrList;
+}
+
+/// Replace direct callers of Old with New. Also add parameters to the call to
+/// \p New, which are defined by the FuncIdx's value in \p Params.
+bool MergeFuncIgnoringConstImpl::replaceDirectCallers(Function *Old,
+ Function *New,
+ const ParamInfos &Params,
+ unsigned FuncIdx) {
+ bool AllReplaced = true;
+
+ SmallVector<CallInst *, 8> Callers;
+
+ for (Use &U : Old->uses()) {
+ auto *I = dyn_cast<Instruction>(U.getUser());
+ if (!I) {
+ AllReplaced = false;
+ continue;
+ }
+ FunctionEntry *FE = getEntry(I->getFunction());
+ if (FE)
+ removeEquivalenceClassFromTree(FE);
+
+ auto *CI = dyn_cast<CallInst>(I);
+ if (!CI || CI->getCalledOperand() != Old) {
+ AllReplaced = false;
+ continue;
+ }
+ Callers.push_back(CI);
+ }
+ if (!AllReplaced)
+ return false;
+
+ // When AlwaysCallThunk is true, return false so a thunk will be emitted, also
+ // do not replace callsites.
+ if (AlwaysCallThunk)
+ return false;
+
+ for (CallInst *CI : Callers) {
+ auto &Context = New->getContext();
+ auto NewPAL = New->getAttributes();
+
+ SmallVector<Type *, 8> OldParamTypes;
+ SmallVector<Value *, 16> NewArgs;
+ SmallVector<AttributeSet, 8> NewArgAttrs;
+ IRBuilder<> Builder(CI);
+
+ FunctionType *NewFuncTy = New->getFunctionType();
+ (void)NewFuncTy;
+ unsigned ParamIdx = 0;
+
+ // Add the existing parameters.
+ for (Value *OldArg : CI->args()) {
+ NewArgAttrs.push_back(NewPAL.getParamAttrs(ParamIdx));
+ NewArgs.push_back(OldArg);
+ OldParamTypes.push_back(OldArg->getType());
+ ++ParamIdx;
+ }
+ // Add the new parameters.
+ for (const ParamInfo &PI : Params) {
+ assert(ParamIdx < NewFuncTy->getNumParams());
+ Constant *ArgValue = getFunctionValue(PI, FuncIdx);
+ assert(ArgValue != Old && "should not try to replace all callers of self "
+ "referencing functions");
+ NewArgs.push_back(ArgValue);
+ OldParamTypes.push_back(ArgValue->getType());
+ ++ParamIdx;
+ }
+
+ auto *FType = FunctionType::get(Old->getFunctionType()->getReturnType(),
+ OldParamTypes, false);
+ auto *FPtrType = PointerType::get(
+ FType, cast<PointerType>(New->getType())->getAddressSpace());
+
+ Value *Callee = ConstantExpr::getBitCast(New, FPtrType);
----------------
nikic wrote:
Unnecessary bitcast
https://github.com/llvm/llvm-project/pull/71584
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