Bitcode: Serialize (and recover) use-list order
Predict and serialize use-list order in bitcode. This makes the option
`-preserve-bc-use-list-order` work *most* of the time, but this is still
experimental.
- Builds a full value-table up front in the writer, sets up a list of
use-list orders to write out, and discards the table. This is a
simpler first step than determining the order from the various
overlapping IDs of values on-the-fly.
- The shuffles stored in the use-list order list have an unnecessarily
large memory footprint.
- `blockaddress` expressions cause functions to be materialized
out-of-order. For now I've ignored this problem, so use-list orders
will be wrong for constants used by functions that have block
addresses taken. There are a couple of ways to fix this, but I
don't have a concrete plan yet.
- When materializing functions lazily, the use-lists for constants
will not be correct. This use case is out of scope: what should the
use-list order be, if it's incomplete?
This is part of PR5680.
llvm-svn: 214125
diff --git a/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp b/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
index 1430fad..0421332 100644
--- a/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
+++ b/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
@@ -25,14 +25,207 @@
#include <algorithm>
using namespace llvm;
+namespace {
+typedef DenseMap<const Value *, std::pair<unsigned, bool>> OrderMap;
+}
+
+static void orderValue(const Value *V, OrderMap &OM) {
+ if (OM.lookup(V).first)
+ return;
+
+ if (const Constant *C = dyn_cast<Constant>(V))
+ if (C->getNumOperands() && !isa<GlobalValue>(C))
+ for (const Value *Op : C->operands())
+ if (!isa<BasicBlock>(Op))
+ orderValue(Op, OM);
+
+ // Note: we cannot cache this lookup above, since inserting into the map
+ // changes the map's size, and thus affects the ID.
+ OM[V].first = OM.size() + 1;
+}
+
+static OrderMap orderModule(const Module *M) {
+ // This needs to match the order used by ValueEnumerator::ValueEnumerator()
+ // and ValueEnumerator::incorporateFunction().
+ OrderMap OM;
+
+ for (const GlobalVariable &G : M->globals())
+ orderValue(&G, OM);
+ for (const Function &F : *M)
+ orderValue(&F, OM);
+ for (const GlobalAlias &A : M->aliases())
+ orderValue(&A, OM);
+ for (const GlobalVariable &G : M->globals())
+ if (G.hasInitializer())
+ orderValue(G.getInitializer(), OM);
+ for (const GlobalAlias &A : M->aliases())
+ orderValue(A.getAliasee(), OM);
+ for (const Function &F : *M)
+ if (F.hasPrefixData())
+ orderValue(F.getPrefixData(), OM);
+
+ for (const Function &F : *M) {
+ if (F.isDeclaration())
+ continue;
+ // Here we need to match the union of ValueEnumerator::incorporateFunction()
+ // and WriteFunction(). Basic blocks are implicitly declared before
+ // anything else (by declaring their size).
+ for (const BasicBlock &BB : F)
+ orderValue(&BB, OM);
+ for (const Argument &A : F.args())
+ orderValue(&A, OM);
+ for (const BasicBlock &BB : F)
+ for (const Instruction &I : BB)
+ for (const Value *Op : I.operands())
+ if ((isa<Constant>(*Op) && !isa<GlobalValue>(*Op)) ||
+ isa<InlineAsm>(*Op))
+ orderValue(Op, OM);
+ for (const BasicBlock &BB : F)
+ for (const Instruction &I : BB)
+ orderValue(&I, OM);
+ }
+ return OM;
+}
+
+static void predictValueUseListOrderImpl(const Value *V, const Function *F,
+ unsigned ID, const OrderMap &OM,
+ UseListOrderStack &Stack) {
+ // Predict use-list order for this one.
+ typedef std::pair<const Use *, unsigned> Entry;
+ SmallVector<Entry, 64> List;
+ for (const Use &U : V->uses())
+ // Check if this user will be serialized.
+ if (OM.lookup(U.getUser()).first)
+ List.push_back(std::make_pair(&U, List.size()));
+
+ if (List.size() < 2)
+ // We may have lost some users.
+ return;
+
+ std::sort(List.begin(), List.end(),
+ [&OM, ID](const Entry &L, const Entry &R) {
+ const Use *LU = L.first;
+ const Use *RU = R.first;
+ auto LID = OM.lookup(LU->getUser()).first;
+ auto RID = OM.lookup(RU->getUser()).first;
+ // If ID is 4, then expect: 7 6 5 1 2 3.
+ if (LID < RID) {
+ if (RID < ID)
+ return true;
+ return false;
+ }
+ if (RID < LID) {
+ if (LID < ID)
+ return false;
+ return true;
+ }
+ // LID and RID are equal, so we have different operands of the same user.
+ // Assume operands are added in order for all instructions.
+ if (LU->getOperandNo() < RU->getOperandNo())
+ return LID < ID;
+ return ID < LID;
+ });
+
+ if (std::is_sorted(
+ List.begin(), List.end(),
+ [](const Entry &L, const Entry &R) { return L.second < R.second; }))
+ // Order is already correct.
+ return;
+
+ // Store the shuffle.
+ UseListOrder O;
+ O.V = V;
+ O.F = F;
+ for (auto &I : List)
+ O.Shuffle.push_back(I.second);
+ Stack.push_back(O);
+}
+
+static void predictValueUseListOrder(const Value *V, const Function *F,
+ OrderMap &OM, UseListOrderStack &Stack) {
+ auto &IDPair = OM[V];
+ assert(IDPair.first && "Unmapped value");
+ if (IDPair.second)
+ // Already predicted.
+ return;
+
+ // Do the actual prediction.
+ IDPair.second = true;
+ if (!V->use_empty() && std::next(V->use_begin()) != V->use_end())
+ predictValueUseListOrderImpl(V, F, IDPair.first, OM, Stack);
+
+ // Recursive descent into constants.
+ if (const Constant *C = dyn_cast<Constant>(V))
+ if (C->getNumOperands() && !isa<GlobalValue>(C))
+ for (const Value *Op : C->operands())
+ if (isa<Constant>(Op) && !isa<GlobalValue>(Op))
+ predictValueUseListOrder(Op, F, OM, Stack);
+}
+
+static UseListOrderStack predictUseListOrder(const Module *M) {
+ OrderMap OM = orderModule(M);
+
+ // Use-list orders need to be serialized after all the users have been added
+ // to a value, or else the shuffles will be incomplete. Store them per
+ // function in a stack.
+ //
+ // Aside from function order, the order of values doesn't matter much here.
+ UseListOrderStack Stack;
+
+ // We want to visit the functions backward now so we can list function-local
+ // constants in the last Function they're used in. Module-level constants
+ // have already been visited above.
+ for (auto I = M->rbegin(), E = M->rend(); I != E; ++I) {
+ const Function &F = *I;
+ if (F.isDeclaration())
+ continue;
+ for (const BasicBlock &BB : F)
+ predictValueUseListOrder(&BB, &F, OM, Stack);
+ for (const Argument &A : F.args())
+ predictValueUseListOrder(&A, &F, OM, Stack);
+ for (const BasicBlock &BB : F)
+ for (const Instruction &I : BB)
+ for (const Value *Op : I.operands())
+ if ((isa<Constant>(*Op) && !isa<GlobalValue>(*Op)) ||
+ isa<InlineAsm>(*Op))
+ predictValueUseListOrder(Op, &F, OM, Stack);
+ for (const BasicBlock &BB : F)
+ for (const Instruction &I : BB)
+ predictValueUseListOrder(&I, &F, OM, Stack);
+ }
+
+ // Visit globals last, since the module-level use-list block will be seen
+ // before the function bodies are processed.
+ for (const GlobalVariable &G : M->globals())
+ predictValueUseListOrder(&G, nullptr, OM, Stack);
+ for (const Function &F : *M)
+ predictValueUseListOrder(&F, nullptr, OM, Stack);
+ for (const GlobalAlias &A : M->aliases())
+ predictValueUseListOrder(&A, nullptr, OM, Stack);
+ for (const GlobalVariable &G : M->globals())
+ if (G.hasInitializer())
+ predictValueUseListOrder(G.getInitializer(), nullptr, OM, Stack);
+ for (const GlobalAlias &A : M->aliases())
+ predictValueUseListOrder(A.getAliasee(), nullptr, OM, Stack);
+ for (const Function &F : *M)
+ if (F.hasPrefixData())
+ predictValueUseListOrder(F.getPrefixData(), nullptr, OM, Stack);
+
+ return Stack;
+}
+
static bool isIntOrIntVectorValue(const std::pair<const Value*, unsigned> &V) {
return V.first->getType()->isIntOrIntVectorTy();
}
/// ValueEnumerator - Enumerate module-level information.
ValueEnumerator::ValueEnumerator(const Module *M) {
+ if (shouldPreserveBitcodeUseListOrder())
+ UseListOrders = predictUseListOrder(M);
+
// Enumerate the global variables.
for (Module::const_global_iterator I = M->global_begin(),
+
E = M->global_end(); I != E; ++I)
EnumerateValue(I);