#include "llvm/Function.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Instructions.h"
+#include "llvm/ParameterAttributes.h"
#include "llvm/Value.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
+#include "llvm/Target/TargetData.h"
using namespace llvm;
//===----------------------------------------------------------------------===//
AU.addRequired<DominatorTree>();
AU.addRequired<MemoryDependenceAnalysis>();
AU.addRequired<AliasAnalysis>();
+ AU.addRequired<TargetData>();
AU.addPreserved<AliasAnalysis>();
AU.addPreserved<MemoryDependenceAnalysis>();
+ AU.addPreserved<TargetData>();
}
// Helper fuctions
SmallVector<Instruction*, 4>& toErase);
bool processNonLocalLoad(LoadInst* L,
SmallVector<Instruction*, 4>& toErase);
- bool processMemCpy(MemCpyInst* M, SmallVector<Instruction*, 4>& toErase);
+ bool processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
+ SmallVector<Instruction*, 4>& toErase);
+ bool performReturnSlotOptzn(MemCpyInst* cpy, CallInst* C,
+ SmallVector<Instruction*, 4>& toErase);
Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
DenseMap<BasicBlock*, Value*> &Phis,
bool top_level = false);
PN->addIncoming(val, *PI);
}
+ AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
+ AA.copyValue(orig, PN);
// Attempt to collapse PHI nodes that are trivially redundant
Value* v = CollapsePhi(PN);
dep = MD.getDependency(L, dep);
}
}
-
+
+ if (dep != MemoryDependenceAnalysis::None &&
+ dep != MemoryDependenceAnalysis::NonLocal &&
+ isa<AllocationInst>(dep)) {
+ // Check that this load is actually from the
+ // allocation we found
+ Value* v = L->getOperand(0);
+ while (true) {
+ if (BitCastInst *BC = dyn_cast<BitCastInst>(v))
+ v = BC->getOperand(0);
+ else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v))
+ v = GEP->getOperand(0);
+ else
+ break;
+ }
+ if (v == dep) {
+ // If this load depends directly on an allocation, there isn't
+ // anything stored there; therefore, we can optimize this load
+ // to undef.
+ MD.removeInstruction(L);
+
+ L->replaceAllUsesWith(UndefValue::get(L->getType()));
+ toErase.push_back(L);
+ deletedLoad = true;
+ NumGVNLoad++;
+ }
+ }
+
if (!deletedLoad)
last = L;
return deletedLoad;
}
+/// isReturnSlotOptznProfitable - Determine if performing a return slot
+/// fusion with the slot dest is profitable
+static bool isReturnSlotOptznProfitable(Value* dest, MemCpyInst* cpy) {
+ // We currently consider it profitable if dest is otherwise dead.
+ SmallVector<User*, 8> useList(dest->use_begin(), dest->use_end());
+ while (!useList.empty()) {
+ User* UI = useList.back();
+
+ if (isa<GetElementPtrInst>(UI) || isa<BitCastInst>(UI)) {
+ useList.pop_back();
+ for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
+ I != E; ++I)
+ useList.push_back(*I);
+ } else if (UI == cpy)
+ useList.pop_back();
+ else
+ return false;
+ }
+
+ return true;
+}
+
+/// performReturnSlotOptzn - takes a memcpy and a call that it depends on,
+/// and checks for the possibility of a return slot optimization by having
+/// the call write its result directly into the callees return parameter
+/// rather than using memcpy
+bool GVN::performReturnSlotOptzn(MemCpyInst* cpy, CallInst* C,
+ SmallVector<Instruction*, 4>& toErase) {
+ // Deliberately get the source and destination with bitcasts stripped away,
+ // because we'll need to do type comparisons based on the underlying type.
+ Value* cpyDest = cpy->getDest();
+ Value* cpySrc = cpy->getSource();
+ CallSite CS = CallSite::get(C);
+
+ // Since this is a return slot optimization, we need to make sure that
+ // the value being copied is, in fact, in a return slot. We also need to
+ // check that the return slot parameter is marked noalias, so that we can
+ // be sure that changing it will not cause unexpected behavior changes due
+ // to it being accessed through a global or another parameter.
+ if (CS.arg_size() == 0 ||
+ cpySrc != CS.getArgument(0) ||
+ !CS.paramHasAttr(1, ParamAttr::NoAlias | ParamAttr::StructRet))
+ return false;
+
+ // Check that something sneaky is not happening involving casting
+ // return slot types around.
+ if (CS.getArgument(0)->getType() != cpyDest->getType())
+ return false;
+ // sret --> pointer
+ const PointerType* PT = cast<PointerType>(cpyDest->getType());
+
+ // We can only perform the transformation if the size of the memcpy
+ // is constant and equal to the size of the structure.
+ ConstantInt* cpyLength = dyn_cast<ConstantInt>(cpy->getLength());
+ if (!cpyLength)
+ return false;
+
+ TargetData& TD = getAnalysis<TargetData>();
+ if (TD.getTypeStoreSize(PT->getElementType()) != cpyLength->getZExtValue())
+ return false;
+
+ // We only perform the transformation if it will be profitable.
+ if (!isReturnSlotOptznProfitable(cpyDest, cpy))
+ return false;
+
+ // In addition to knowing that the call does not access the return slot
+ // in some unexpected manner, which we derive from the noalias attribute,
+ // we also need to know that it does not sneakily modify the destination
+ // slot in the caller. We don't have parameter attributes to go by
+ // for this one, so we just rely on AA to figure it out for us.
+ AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
+ if (AA.getModRefInfo(C, cpy->getRawDest(), cpyLength->getZExtValue()) !=
+ AliasAnalysis::NoModRef)
+ return false;
+
+ // If all the checks have passed, then we're alright to do the transformation.
+ CS.setArgument(0, cpyDest);
+
+ // Drop any cached information about the call, because we may have changed
+ // its dependence information by changing its parameter.
+ MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
+ MD.dropInstruction(C);
+
+ // Remove the memcpy
+ MD.removeInstruction(cpy);
+ toErase.push_back(cpy);
+
+ return true;
+}
+
/// processMemCpy - perform simplication of memcpy's. If we have memcpy A which
/// copies X to Y, and memcpy B which copies Y to Z, then we can rewrite B to be
/// a memcpy from X to Z (or potentially a memmove, depending on circumstances).
/// This allows later passes to remove the first memcpy altogether.
-bool GVN::processMemCpy(MemCpyInst* M,
+bool GVN::processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
SmallVector<Instruction*, 4>& toErase) {
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-
- // First, we have to check that the dependency is another memcpy
- Instruction* dep = MD.getDependency(M);
- if (dep == MemoryDependenceAnalysis::None ||
- dep == MemoryDependenceAnalysis::NonLocal ||
- !isa<MemCpyInst>(dep))
- return false;
-
// We can only transforms memcpy's where the dest of one is the source of the
// other
- MemCpyInst* MDep = cast<MemCpyInst>(dep);
if (M->getSource() != MDep->getDest())
return false;
// Second, the length of the memcpy's must be the same, or the preceeding one
// must be larger than the following one.
- Value* DepLength = MDep->getLength();
- uint64_t CpySize = ~0UL;
- uint64_t DepSize = ~0UL;
- if (isa<ConstantInt>(DepLength)) {
- if (isa<ConstantInt>(M->getLength())) {
- if (cast<ConstantInt>(DepLength)->getLimitedValue() <
- cast<ConstantInt>(M->getLength())->getLimitedValue()) {
- return false;
- } else {
- CpySize = cast<ConstantInt>(M->getLength())->getLimitedValue();
- DepSize = cast<ConstantInt>(DepLength)->getLimitedValue();
- }
- } else {
- return false;
- }
- } else {
+ ConstantInt* C1 = dyn_cast<ConstantInt>(MDep->getLength());
+ ConstantInt* C2 = dyn_cast<ConstantInt>(M->getLength());
+ if (!C1 || !C2)
+ return false;
+
+ uint64_t CpySize = C1->getValue().getZExtValue();
+ uint64_t DepSize = C2->getValue().getZExtValue();
+
+ if (DepSize < CpySize)
return false;
- }
// Finally, we have to make sure that the dest of the second does not
// alias the source of the first
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) !=
- AliasAnalysis::NoAlias) {
- // If they don't, we can still make the transformation by first turning M
- // into a memmove rather than a memcpy.
- bool is32bit = M->getIntrinsicID() == Intrinsic::memcpy_i32;
- Function* MemMoveFun = Intrinsic::getDeclaration(
+ AliasAnalysis::NoAlias)
+ return false;
+ else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) !=
+ AliasAnalysis::NoAlias)
+ return false;
+ else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize)
+ != AliasAnalysis::NoAlias)
+ return false;
+
+ // If all checks passed, then we can transform these memcpy's
+ Function* MemCpyFun = Intrinsic::getDeclaration(
M->getParent()->getParent()->getParent(),
- is32bit ? Intrinsic::memmove_i32 :
- Intrinsic::memmove_i64);
-
- std::vector<Value*> args;
- args.push_back(M->getRawDest());
- args.push_back(MDep->getRawSource());
- args.push_back(M->getLength());
- args.push_back(M->getAlignment());
-
- new CallInst(MemMoveFun, args.begin(), args.end(), "", M);
+ M->getIntrinsicID());
- MD.removeInstruction(M);
+ std::vector<Value*> args;
+ args.push_back(M->getRawDest());
+ args.push_back(MDep->getRawSource());
+ args.push_back(M->getLength());
+ args.push_back(M->getAlignment());
+
+ CallInst* C = new CallInst(MemCpyFun, args.begin(), args.end(), "", M);
+
+ MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
+ if (MD.getDependency(C) == MDep) {
+ MD.dropInstruction(M);
toErase.push_back(M);
-
return true;
+ } else {
+ MD.removeInstruction(C);
+ toErase.push_back(C);
+ return false;
}
-
- // If all checks passed, then we can transform these memcpy's
- M->setSource(MDep->getRawSource());
-
- // Reset dependence information for the memcpy
- MD.removeInstruction(M);
-
- return true;
}
/// processInstruction - When calculating availability, handle an instruction
if (LoadInst* L = dyn_cast<LoadInst>(I)) {
return processLoad(L, lastSeenLoad, toErase);
} else if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) {
- return processMemCpy(M, toErase);
+ MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
+
+ // The are two possible optimizations we can do for memcpy:
+ // a) memcpy-memcpy xform which exposes redundance for DSE
+ // b) call-memcpy xform for sret return slot optimization
+ Instruction* dep = MD.getDependency(M);
+ if (dep == MemoryDependenceAnalysis::None ||
+ dep == MemoryDependenceAnalysis::NonLocal)
+ return false;
+ if (MemCpyInst *MemCpy = dyn_cast<MemCpyInst>(dep))
+ return processMemCpy(M, MemCpy, toErase);
+ if (CallInst* C = dyn_cast<CallInst>(dep))
+ return performReturnSlotOptzn(M, C, toErase);
+ return false;
}
unsigned num = VN.lookup_or_add(I);
++BI;
for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
- E = toErase.end(); I != E; ++I)
+ E = toErase.end(); I != E; ++I) {
(*I)->eraseFromParent();
+ }
toErase.clear();
}
projects / oota-llvm.git / blobdiff