+//===- SplitModule.cpp - Split a module into partitions -------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the function llvm::SplitModule, which splits a module
+// into multiple linkable partitions. It can be used to implement parallel code
+// generation for link-time optimization.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/SplitModule.h"
+#include "llvm/ADT/Hashing.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GlobalAlias.h"
+#include "llvm/IR/GlobalObject.h"
+#include "llvm/IR/GlobalValue.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/MD5.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/Cloning.h"
+
+using namespace llvm;
+
+static void externalize(GlobalValue *GV) {
+ if (GV->hasLocalLinkage()) {
+ GV->setLinkage(GlobalValue::ExternalLinkage);
+ GV->setVisibility(GlobalValue::HiddenVisibility);
+ }
+
+ // Unnamed entities must be named consistently between modules. setName will
+ // give a distinct name to each such entity.
+ if (!GV->hasName())
+ GV->setName("__llvmsplit_unnamed");
+}
+
+// Returns whether GV should be in partition (0-based) I of N.
+static bool isInPartition(const GlobalValue *GV, unsigned I, unsigned N) {
+ if (auto GA = dyn_cast<GlobalAlias>(GV))
+ if (const GlobalObject *Base = GA->getBaseObject())
+ GV = Base;
+
+ StringRef Name;
+ if (const Comdat *C = GV->getComdat())
+ Name = C->getName();
+ else
+ Name = GV->getName();
+
+ // Partition by MD5 hash. We only need a few bits for evenness as the number
+ // of partitions will generally be in the 1-2 figure range; the low 16 bits
+ // are enough.
+ MD5 H;
+ MD5::MD5Result R;
+ H.update(Name);
+ H.final(R);
+ return (R[0] | (R[1] << 8)) % N == I;
+}
+
+void llvm::SplitModule(
+ std::unique_ptr<Module> M, unsigned N,
+ std::function<void(std::unique_ptr<Module> MPart)> ModuleCallback) {
+ for (Function &F : *M)
+ externalize(&F);
+ for (GlobalVariable &GV : M->globals())
+ externalize(&GV);
+ for (GlobalAlias &GA : M->aliases())
+ externalize(&GA);
+
+ // FIXME: We should be able to reuse M as the last partition instead of
+ // cloning it.
+ for (unsigned I = 0; I != N; ++I) {
+ ValueToValueMapTy VMap;
+ std::unique_ptr<Module> MPart(
+ CloneModule(M.get(), VMap, [=](const GlobalValue *GV) {
+ return isInPartition(GV, I, N);
+ }));
+ if (I != 0)
+ MPart->setModuleInlineAsm("");
+ ModuleCallback(std::move(MPart));
+ }
+}
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