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Make a few major changes to memdep and its clients:

Browse Source 
1. Merge the 'None' result into 'Normal', making loads
   and stores return their dependencies on allocations as Normal.
2. Split the 'Normal' result into 'Clobber' and 'Def' to
   distinguish between the cases when memdep knows the value is
   produced from when we just know if may be changed.
3. Move some of the logic for determining whether readonly calls
   are CSEs into memdep instead of it being in GVN.  This still
   leaves verification that the arguments are hte same to GVN to
   let it know about value equivalences in different contexts.
4. Change memdep's call/call dependency analysis to use 
   getModRefInfo(CallSite,CallSite) instead of doing something 
   very weak.  This only really matters for things like DSA, but
   someday maybe we'll have some other decent context sensitive
   analyses :)
5. This reimplements the guts of memdep to handle the new results.
6. This simplifies GVN significantly:
   a) readonly call CSE is slightly simpler
   b) I eliminated the "getDependencyFrom" chaining for load 
      elimination and load CSE doesn't have to worry about 
      volatile (they are always clobbers) anymore.
   c) GVN no longer does any 'lastLoad' caching, leaving it to 
      memdep.
7. The logic in DSE is simplified a bit and sped up.  A potentially
   unsafe case was eliminated.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60607 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2008-12-05 21:04:20 +00:00
parent 56d9b6dff3
commit b51deb929c
5 changed files with 177 additions and 185 deletions
Download Patch File Download Diff File Expand all files Collapse all files

175
lib/Transforms/Scalar/GVN.cpp
View File

@ -461,30 +461,19 @@ uint32_t ValueTable::lookup_or_add(Value* V) {
MemDepResult local_dep = MD->getDependency(C);
if (local_dep.isNone()) {
if (!local_dep.isDef() && !local_dep.isNonLocal()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
if (Instruction *LocalDepInst = local_dep.getInst()) {
if (!isa<CallInst>(LocalDepInst)) {
if (local_dep.isDef()) {
CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
if (local_cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
CallInst* local_cdep = cast<CallInst>(LocalDepInst);
if (local_cdep->getCalledFunction() != C->getCalledFunction() ||
local_cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
if (!C->getCalledFunction()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
for (unsigned i = 1; i < C->getNumOperands(); ++i) {
uint32_t c_vn = lookup_or_add(C->getOperand(i));
uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
@ -498,10 +487,12 @@ uint32_t ValueTable::lookup_or_add(Value* V) {
valueNumbering.insert(std::make_pair(V, v));
return v;
}
// Non-local case.
const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
MD->getNonLocalDependency(C);
// FIXME: call/call dependencies for readonly calls should return def, not
// clobber! Move the checking logic to MemDep!
CallInst* cdep = 0;
// Check to see if we have a single dominating call instruction that is
@ -514,7 +505,7 @@ uint32_t ValueTable::lookup_or_add(Value* V) {
// We don't handle non-depedencies. If we already have a call, reject
// instruction dependencies.
if (I->second.isNone() || cdep != 0) {
if (I->second.isClobber() || cdep != 0) {
cdep = 0;
break;
}
@ -535,12 +526,7 @@ uint32_t ValueTable::lookup_or_add(Value* V) {
return nextValueNumber++;
}
if (cdep->getCalledFunction() != C->getCalledFunction() ||
cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
if (!C->getCalledFunction()) {
if (cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
@ -736,10 +722,8 @@ namespace {
// Helper fuctions
// FIXME: eliminate or document these better
bool processLoad(LoadInst* L,
DenseMap<Value*, LoadInst*> &lastLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processInstruction(Instruction* I,
DenseMap<Value*, LoadInst*>& lastSeenLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processNonLocalLoad(LoadInst* L,
SmallVectorImpl<Instruction*> &toErase);
@ -979,7 +963,15 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
continue;
}
if (DepInfo.isNone()) {
if (DepInfo.isClobber()) {
UnavailableBlocks.push_back(DepBB);
continue;
}
Instruction *DepInst = DepInfo.getInst();
// Loading the allocation -> undef.
if (isa<AllocationInst>(DepInst)) {
ValuesPerBlock.push_back(std::make_pair(DepBB,
UndefValue::get(LI->getType())));
continue;
@ -996,13 +988,6 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
continue;
}
if (S->getPointerOperand() != LI->getPointerOperand() &&
VN.getAliasAnalysis()->alias(S->getPointerOperand(), 1,
LI->getPointerOperand(), 1)
!= AliasAnalysis::MustAlias) {
UnavailableBlocks.push_back(DepBB);
continue;
}
ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
} else if (LoadInst* LD = dyn_cast<LoadInst>(DepInfo.getInst())) {
@ -1010,14 +995,6 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
UnavailableBlocks.push_back(DepBB);
continue;
}
if (LD->getPointerOperand() != LI->getPointerOperand() &&
VN.getAliasAnalysis()->alias(LD->getPointerOperand(), 1,
LI->getPointerOperand(), 1)
!= AliasAnalysis::MustAlias) {
UnavailableBlocks.push_back(DepBB);
continue;
}
ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
} else {
UnavailableBlocks.push_back(DepBB);
@ -1156,84 +1133,64 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
/// processLoad - Attempt to eliminate a load, first by eliminating it
/// locally, and then attempting non-local elimination if that fails.
bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad,
SmallVectorImpl<Instruction*> &toErase) {
if (L->isVolatile()) {
lastLoad[L->getPointerOperand()] = L;
bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
if (L->isVolatile())
return false;
}
Value* pointer = L->getPointerOperand();
LoadInst*& last = lastLoad[pointer];
// ... to a pointer that has been loaded from before...
bool removedNonLocal = false;
MemDepResult dep = MD->getDependency(L);
if (dep.isNonLocal() &&
L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
removedNonLocal = processNonLocalLoad(L, toErase);
if (!removedNonLocal)
last = L;
return removedNonLocal;
}
bool deletedLoad = false;
// Walk up the dependency chain until we either find
// a dependency we can use, or we can't walk any further
while (Instruction *DepInst = dep.getInst()) {
// ... that depends on a store ...
if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
if (S->getPointerOperand() == pointer) {
// Remove it!
L->replaceAllUsesWith(S->getOperand(0));
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
}
// Whether we removed it or not, we can't
// go any further
break;
} else if (!isa<LoadInst>(DepInst)) {
// Only want to handle loads below.
break;
} else if (!last) {
// If we don't depend on a store, and we haven't
// been loaded before, bail.
break;
} else if (DepInst == last) {
// Remove it!
L->replaceAllUsesWith(last);
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
break;
} else {
dep = MD->getDependencyFrom(L, DepInst, DepInst->getParent());
}
// If the value isn't available, don't do anything!
if (dep.isClobber())
return false;
// If it is defined in another block, try harder.
if (dep.isNonLocal()) {
if (L->getParent() == &L->getParent()->getParent()->getEntryBlock())
return false;
return processNonLocalLoad(L, toErase);
}
Instruction *DepInst = dep.getInst();
if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
// Only forward substitute stores to loads of the same type.
// FIXME: Could do better!
if (DepSI->getPointerOperand()->getType() != pointer->getType())
return false;
// Remove it!
L->replaceAllUsesWith(DepSI->getOperand(0));
toErase.push_back(L);
NumGVNLoad++;
return true;
}
if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
// Only forward substitute stores to loads of the same type.
// FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
if (DepLI->getType() != L->getType())
return false;
// Remove it!
L->replaceAllUsesWith(DepLI);
toErase.push_back(L);
NumGVNLoad++;
return true;
}
// If this load really doesn't depend on anything, then we must be loading an
// undef value. This can happen when loading for a fresh allocation with no
// intervening stores, for example.
if (dep.isNone()) {
// If this load depends directly on an allocation, there isn't
// anything stored there; therefore, we can optimize this load
// to undef.
if (isa<AllocationInst>(DepInst)) {
L->replaceAllUsesWith(UndefValue::get(L->getType()));
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
return true;
}
if (!deletedLoad)
last = L;
return deletedLoad;
return false;
}
Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
@ -1257,10 +1214,9 @@ Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
/// processInstruction - When calculating availability, handle an instruction
/// by inserting it into the appropriate sets
bool GVN::processInstruction(Instruction *I,
DenseMap<Value*, LoadInst*> &lastSeenLoad,
SmallVectorImpl<Instruction*> &toErase) {
if (LoadInst* L = dyn_cast<LoadInst>(I)) {
bool changed = processLoad(L, lastSeenLoad, toErase);
bool changed = processLoad(L, toErase);
if (!changed) {
unsigned num = VN.lookup_or_add(L);
@ -1362,7 +1318,6 @@ bool GVN::runOnFunction(Function& F) {
bool GVN::processBlock(DomTreeNode* DTN) {
BasicBlock* BB = DTN->getBlock();
SmallVector<Instruction*, 8> toErase;
DenseMap<Value*, LoadInst*> lastSeenLoad;
bool changed_function = false;
if (DTN->getIDom())
@ -1373,7 +1328,7 @@ bool GVN::processBlock(DomTreeNode* DTN) {
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE;) {
changed_function |= processInstruction(BI, lastSeenLoad, toErase);
changed_function |= processInstruction(BI, toErase);
if (toErase.empty()) {
++BI;
continue;