[llvm-commits] [llvm] r53606 - /llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp
Matthijs Kooijman
matthijs at stdin.nl
Tue Jul 15 06:36:10 PDT 2008
Author: matthijs
Date: Tue Jul 15 08:36:06 2008
New Revision: 53606
URL: http://llvm.org/viewvc/llvm-project?rev=53606&view=rev
Log:
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.
Modified:
llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp
Modified: llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp?rev=53606&r1=53605&r2=53606&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp Tue Jul 15 08:36:06 2008
@@ -47,12 +47,14 @@
/// 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 @@
}
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 @@
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 @@
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 @@
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 @@
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 @@
// 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 @@
}
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 @@
// 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 @@
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 @@
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 @@
// 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 @@
++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 @@
// 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 @@
++NumArgumentsEliminated;
DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart()
<< ") from " << F->getNameStart() << "\n";
- Changed = true;
}
}
@@ -714,11 +714,6 @@
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 @@
"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 @@
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);
More information about the llvm-commits
mailing list