maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

Make DeadArgElim keep liveness of the return value as a whole in addition to 

only the liveness of partial return values (for functions returning a struct).
This is more explicit to prevent unwanted changes in the return value. 

In particular, deadargelim now canonicalizes a function returning {i32} to
returning i32 and {} to void, if the struct returned is not used in its
entirety, but only the single element is used.

llvm-svn: 53606
This commit is contained in:
Matthijs Kooijman 2008-07-15 13:36:06 +00:00
parent d337446b8e
commit 84194b6768
1 changed files with 124 additions and 126 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

250
llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
View File

@ -47,12 +47,14 @@ namespace {
/// Struct that represents (part of) either a return value or a function
/// argument. Used so that arguments and return values can be used
/// interchangably.
/// interchangably. Idx == -1 means the entire return value, while other
/// indices mean the corresponding element in the struct return type (if
/// any).
struct RetOrArg {
RetOrArg(const Function* F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
RetOrArg(const Function* F, signed Idx, bool IsArg) : F(F), Idx(Idx),
IsArg(IsArg) {}
const Function *F;
unsigned Idx;
signed Idx;
bool IsArg;
/// Make RetOrArg comparable, so we can put it into a map.
@ -71,8 +73,10 @@ namespace {
}
std::string getDescription() const {
return std::string((IsArg ? "Argument #" : "Return value #"))
+ utostr(Idx) + " of function " + F->getName();
return std::string((!IsArg && Idx != -1 ? "partial " : ""))
+ (IsArg ? "argument #" : "return value")
+ (!IsArg && Idx == -1 ? "" : " #" + utostr(Idx))
+ " of function " + F->getName();
}
};
@ -84,11 +88,11 @@ namespace {
enum Liveness { Live, MaybeLive };
/// Convenience wrapper
RetOrArg CreateRet(const Function *F, unsigned Idx) {
RetOrArg CreateRet(const Function *F, signed Idx) {
return RetOrArg(F, Idx, false);
}
/// Convenience wrapper
RetOrArg CreateArg(const Function *F, unsigned Idx) {
RetOrArg CreateArg(const Function *F, signed Idx) {
return RetOrArg(F, Idx, true);
}
@ -129,7 +133,7 @@ namespace {
private:
Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses,
unsigned RetValNum = 0);
signed RetValNum = -1);
Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses);
void SurveyFunction(Function &F);
@ -278,18 +282,6 @@ bool DAE::DeleteDeadVarargs(Function &Fn) {
return true;
}
/// Convenience function that returns the number of return values. It returns 0
/// for void functions and 1 for functions not returning a struct. It returns
/// the number of struct elements for functions returning a struct.
static unsigned NumRetVals(const Function *F) {
if (F->getReturnType() == Type::VoidTy)
return 0;
else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType()))
return STy->getNumElements();
else
return 1;
}
/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
/// live, it adds Use to the MaybeLiveUses argument. Returns the determined
/// liveness of Use.
@ -304,16 +296,15 @@ DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
return MaybeLive;
}
/// SurveyUse - This looks at a single use of an argument or return value
/// and determines if it should be alive or not. Adds this use to MaybeLiveUses
/// if it causes the used value to become MaybeAlive.
///
/// RetValNum is the return value number to use when this use is used in a
/// return instruction. This is used in the recursion, you should always leave
/// it at 0.
/// it at -1.
DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses,
unsigned RetValNum) {
signed RetValNum) {
Value *V = *U;
if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
// The value is returned from a function. It's only live when the
@ -402,16 +393,23 @@ DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) {
// well as arguments to functions which have their "address taken".
//
void DAE::SurveyFunction(Function &F) {
unsigned RetCount = NumRetVals(&F);
const StructType *STy = dyn_cast<StructType>(F.getFunctionType()->getReturnType());
// Store the number of partial return values, which we only have if the return
// type is a struct.
unsigned PartialRetVals = (STy ? STy->getNumElements() : 0);
// Assume all return values are dead
typedef SmallVector<Liveness, 5> RetVals;
RetVals RetValLiveness(RetCount, MaybeLive);
// Allocate one slot for the entire return value (index 0) and one for each
// partial return value.
RetVals RetValLiveness(PartialRetVals + 1, MaybeLive);
typedef SmallVector<UseVector, 5> RetUses;
// These vectors map each return value to the uses that make it MaybeLive, so
// we can add those to the Uses map if the return value really turns out to be
// MaybeLive. Initialized to a list of RetCount empty lists.
RetUses MaybeLiveRetUses(RetCount);
// MaybeLive.
// Allocate one slot for the entire return value (index 0) and one for each
// partial return value.
RetUses MaybeLiveRetUses(PartialRetVals + 1);
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
@ -428,10 +426,6 @@ void DAE::SurveyFunction(Function &F) {
}
DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n";
// Keep track of the number of live retvals, so we can skip checks once all
// of them turn out to be live.
unsigned NumLiveRetVals = 0;
const Type *STy = dyn_cast<StructType>(F.getReturnType());
// Loop all uses of the function.
for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
// If the function is PASSED IN as an argument, its address has been
@ -452,43 +446,42 @@ void DAE::SurveyFunction(Function &F) {
// If we end up here, we are looking at a direct call to our function.
// Now, check how our return value(s) is/are used in this caller. Don't
// bother checking return values if all of them are live already.
if (NumLiveRetVals != RetCount) {
if (STy) {
// Check all uses of the return value.
for (Value::use_iterator I = TheCall->use_begin(),
E = TheCall->use_end(); I != E; ++I) {
ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
if (Ext && Ext->hasIndices()) {
// This use uses a part of our return value, survey the uses of
// that part and store the results for this index only.
unsigned Idx = *Ext->idx_begin();
if (RetValLiveness[Idx] != Live) {
RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
if (RetValLiveness[Idx] == Live)
NumLiveRetVals++;
}
} else {
// Used by something else than extractvalue. Mark all return
// values as live.
for (unsigned i = 0; i != RetCount; ++i )
RetValLiveness[i] = Live;
NumLiveRetVals = RetCount;
break;
// bother checking return values if the entire value is live already.
if (RetValLiveness[0] != Live) {
// Check all uses of the return value.
for (Value::use_iterator I = TheCall->use_begin(),
E = TheCall->use_end(); I != E; ++I) {
ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
if (Ext && Ext->hasIndices()) {
// This use uses a part of our return value, survey the uses of
// that part and store the results for this index only.
unsigned Idx = *Ext->idx_begin();
// + 1 to skip the "entire retval" index (0)
Liveness &IsLive = RetValLiveness[Idx + 1];
if (IsLive != Live) {
// Don't bother checking if this retval was already live
// Survey all uses of the extractvalue
// + 1 to skip the "entire retval" index (0)
IsLive = SurveyUses(Ext, MaybeLiveRetUses[Idx + 1]);
}
} else {
// Survey this use
RetValLiveness[0] = SurveyUse(I, MaybeLiveRetUses[0]);
if (RetValLiveness[0] == Live)
break;
}
} else {
// Single return value
RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
if (RetValLiveness[0] == Live)
NumLiveRetVals = RetCount;
}
}
}
// Now we've inspected all callers, record the liveness of our return values.
for (unsigned i = 0; i != RetCount; ++i)
MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
MarkValue(CreateRet(&F, -1), RetValLiveness[0], MaybeLiveRetUses[0]);
if (RetValLiveness[0] != Live)
// If the entire retval (0) is Live, MarkValue will have marked all other retvals live
// as well, so we can skip this.
for (unsigned i = 0; i != PartialRetVals; ++i)
// + 1 to skip the "entire retval" index (0)
MarkValue(CreateRet(&F, i), RetValLiveness[i + 1], MaybeLiveRetUses[i + 1]);
DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n";
@ -539,8 +532,11 @@ void DAE::MarkLive(const Function &F) {
for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
PropagateLiveness(CreateArg(&F, i));
// Mark all return values as live.
for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
PropagateLiveness(CreateRet(&F, i));
const Type *RTy = F.getFunctionType()->getReturnType();
if (const StructType *STy = dyn_cast<StructType>(RTy))
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
PropagateLiveness(CreateRet(&F, i));
PropagateLiveness(CreateRet(&F, -1));
}
/// MarkLive - Mark the given return value or argument as live. Additionally,
@ -555,6 +551,16 @@ void DAE::MarkLive(const RetOrArg &RA) {
DOUT << "DAE - Marking " << RA.getDescription() << " live\n";
PropagateLiveness(RA);
if (!RA.IsArg && RA.Idx == -1) {
// Entire return value live?
const Type *RTy = RA.F->getFunctionType()->getReturnType();
if (const StructType *STy = dyn_cast<StructType>(RTy))
// And the function returns a struct?
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
// Mark all partial return values live as well then
MarkLive(CreateRet(RA.F, i));
}
}
/// PropagateLiveness - Given that RA is a live value, propagate it's liveness
@ -599,20 +605,20 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
// Find out the new return value.
const Type *RetTy = FTy->getReturnType();
const StructType *STy = dyn_cast<StructType>(RetTy);
const unsigned PartialRetVals = (STy ? STy->getNumElements() : 0);
const Type *NRetTy = NULL;
unsigned RetCount = NumRetVals(F);
// Explicitly track if anything changed, for debugging.
bool Changed = false;
// -1 means unused, other numbers are the new index
SmallVector<int, 5> NewRetIdxs(RetCount, -1);
// -1 means unused, other numbers are the new index. Initialized to -1 for
// every partial return value we have.
SmallVector<int, 5> NewRetIdxs(PartialRetVals, -1);
std::vector<const Type*> RetTypes;
if (RetTy == Type::VoidTy) {
NRetTy = Type::VoidTy;
if (LiveValues.count(CreateRet(F, -1))) {
// If the entire return value is live, leave it unchanged.
NRetTy = RetTy;
} else {
const StructType *STy = dyn_cast<StructType>(RetTy);
if (STy)
// Look at each of the original return values individually.
for (unsigned i = 0; i != RetCount; ++i) {
if (STy) {
// Look at each of the partial return values individually.
for (unsigned i = 0; i != PartialRetVals; ++i) {
RetOrArg Ret = CreateRet(F, i);
if (LiveValues.erase(Ret)) {
RetTypes.push_back(STy->getElementType(i));
@ -621,25 +627,20 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
++NumRetValsEliminated;
DOUT << "DAE - Removing return value " << i << " from "
<< F->getNameStart() << "\n";
Changed = true;
// We remove the value by not adding anything to RetTypes.
}
}
else
// We used to return a single value.
if (LiveValues.erase(CreateRet(F, 0))) {
RetTypes.push_back(RetTy);
NewRetIdxs[0] = 0;
} else {
DOUT << "DAE - Removing return value from " << F->getNameStart()
<< "\n";
++NumRetValsEliminated;
Changed = true;
}
if (RetTypes.size() > 1 || (STy && STy->getNumElements()==RetTypes.size()))
// More than one return type? Return a struct with them. Also, if we used
// to return a struct and didn't change the number of return values,
// return a struct again. This prevents changing {something} into
// something and {} into void.
} else if (RetTy != Type::VoidTy) {
// We used to return a single value, which is now dead (already checked in
// the if above)
DOUT << "DAE - Removing return value from " << F->getNameStart()
<< "\n";
++NumRetValsEliminated;
// We remove the value by not adding anything to RetTypes.
}
if (RetTypes.size() > 1)
// More than one return type? Return a struct with them.
// Make the new struct packed if we used to return a packed struct
// already.
NRetTy = StructType::get(RetTypes, STy->isPacked());
@ -648,7 +649,7 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
// return a struct with that simple value before.
NRetTy = RetTypes.front();
else if (RetTypes.size() == 0)
// No return types? Make it void, but only if we didn't use to return {}.
// No return types? Make it void.
NRetTy = Type::VoidTy;
}
@ -688,7 +689,6 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
++NumArgumentsEliminated;
DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart()
<< ") from " << F->getNameStart() << "\n";
Changed = true;
}
}
@ -714,11 +714,6 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
if (NFTy == FTy)
return false;
// The function type is only allowed to be different if we actually left out
// an argument or return value.
assert(Changed && "Function type changed while no arguments or return values"
"were removed!");
// Create the new function body and insert it into the module...
Function *NF = Function::Create(NFTy, F->getLinkage());
NF->copyAttributesFrom(F);
@ -803,39 +798,42 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
"void. The old return type must have"
"been a struct!");
// The original return value was a struct, update all uses (which are
// all extractvalue instructions).
// all extractvalue instructions, or uses that are unused themselves).
for (Value::use_iterator I = Call->use_begin(), E = Call->use_end();
I != E;) {
assert(isa<ExtractValueInst>(*I) && "Return value not only used by"
"extractvalue?");
ExtractValueInst *EV = cast<ExtractValueInst>(*I);
// Increment now, since we're about to throw away this use.
++I;
assert(EV->hasIndices() && "Return value used by extractvalue without"
"indices?");
unsigned Idx = *EV->idx_begin();
if (NewRetIdxs[Idx] != -1) {
if (RetTypes.size() > 1) {
// We're still returning a struct, create a new extractvalue
// instruction with the first index updated
std::vector<unsigned> NewIdxs(EV->idx_begin(), EV->idx_end());
NewIdxs[0] = NewRetIdxs[Idx];
Value *NEV = ExtractValueInst::Create(New, NewIdxs.begin(),
NewIdxs.end(), "retval",
EV);
EV->replaceAllUsesWith(NEV);
EV->eraseFromParent();
if (ExtractValueInst *EV = dyn_cast<ExtractValueInst>(*I)) {
// Increment now, since we're about to throw away this use.
++I;
assert(EV->hasIndices() && "Return value used by extractvalue without"
"indices?");
unsigned Idx = *EV->idx_begin();
if (NewRetIdxs[Idx] != -1) {
if (RetTypes.size() > 1) {
// We're still returning a struct, create a new extractvalue
// instruction with the first index updated
std::vector<unsigned> NewIdxs(EV->idx_begin(), EV->idx_end());
NewIdxs[0] = NewRetIdxs[Idx];
Value *NEV = ExtractValueInst::Create(New, NewIdxs.begin(),
NewIdxs.end(), "retval",
EV);
EV->replaceAllUsesWith(NEV);
EV->eraseFromParent();
} else {
// We are now only returning a simple value, remove the
// extractvalue.
EV->replaceAllUsesWith(New);
EV->eraseFromParent();
}
} else {
// We are now only returning a simple value, remove the
// extractvalue.
EV->replaceAllUsesWith(New);
// Value unused, replace uses by null for now, they will get removed
// later on.
EV->replaceAllUsesWith(Constant::getNullValue(EV->getType()));
EV->eraseFromParent();
}
} else {
// Value unused, replace uses by null for now, they will get removed
// later on.
EV->replaceAllUsesWith(Constant::getNullValue(EV->getType()));
EV->eraseFromParent();
// Not an extractvalue, so this use will become dead soon. Just
// replace it with null.
I.getUse().set(Constant::getNullValue(I.getUse().get()->getType()));
}
}
New->takeName(Call);
@ -888,7 +886,7 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
Value *OldRet = RI->getOperand(0);
// Start out building up our return value from undef
RetVal = llvm::UndefValue::get(NRetTy);
for (unsigned i = 0; i != RetCount; ++i)
for (unsigned i = 0; i != PartialRetVals; ++i)
if (NewRetIdxs[i] != -1) {
ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
"oldret", RI);