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Bitcode: Serialize (and recover) use-list order

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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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214125 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith
2014-07-28 21:19:41 +00:00
parent 0aed6e729d
commit bd24fe8c7e
9 changed files with 287 additions and 103 deletions
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193
lib/Bitcode/Writer/ValueEnumerator.cpp
View File

@ -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);