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Change Type::isAbstract to have better comments, a more correct name

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(PromoteAbstractToConcrete), and to use a set to avoid recomputation.
In particular, this set eliminates the potentially exponential cases
from this little recursive algorithm.

On a particularly nasty testcase, llvm-dis on the .bc file went from 34
minutes (which is when I killed it, it still hadn't finished) to 0.57s.
Remember kids, exponential algorithms are bad.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16772 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-10-06 16:36:46 +00:00
parent df00115aa4
commit b5c16705fd
1 changed files with 19 additions and 12 deletions
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31
lib/VMCore/Type.cpp
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@ -443,19 +443,26 @@ void DerivedType::dropAllTypeUses() {
}
}
// isTypeAbstract - This is a recursive function that walks a type hierarchy
// calculating whether or not a type is abstract. Worst case it will have to do
// a lot of traversing if you have some whacko opaque types, but in most cases,
// it will do some simple stuff when it hits non-abstract types that aren't
// recursive.
// PromoteAbstractToConcrete - This is a recursive function that walks a type
// graph calculating whether or not a type is abstract.
//
bool Type::isTypeAbstract() {
// This method returns true if the type is found to still be abstract.
//
bool Type::PromoteAbstractToConcrete(void *Ptr) {
if (!isAbstract()) // Base case for the recursion
return false; // Primitive = leaf type
if (isa<OpaqueType>(this)) // Base case for the recursion
return true; // This whole type is abstract!
/// KnownAbstractTypes - This set contains all of the types that we know for
/// sure are abstract. Once we discover that a type really is abstract, we
/// remember this so we don't have to do potentially exponential amounts of
/// checking in some cases.
std::set<Type*> &KnownAbstractTypes = *(std::set<Type*>*)Ptr;
if (KnownAbstractTypes.count(this))
return true; // We already know this type is abstract!
// We have to guard against recursion. To do this, we temporarily mark this
// type as concrete, so that if we get back to here recursively we will think
// it's not abstract, and thus not scan it again.
@ -465,15 +472,14 @@ bool Type::isTypeAbstract() {
// one!
for (Type::subtype_iterator I = subtype_begin(), E = subtype_end();
I != E; ++I)
if (const_cast<Type*>(I->get())->isTypeAbstract()) {
if (const_cast<Type*>(I->get())->PromoteAbstractToConcrete(Ptr)) {
KnownAbstractTypes.insert(this);
setAbstract(true); // Restore the abstract bit.
return true; // This type is abstract if subtype is abstract!
}
// Restore the abstract bit.
setAbstract(true);
// Nothing looks abstract here...
// Nothing looks abstract here.
setAbstract(false);
return false;
}
@ -725,7 +731,8 @@ public:
// If the type is currently thought to be abstract, rescan all of our
// subtypes to see if the type has just become concrete!
if (Ty->isAbstract()) {
Ty->setAbstract(Ty->isTypeAbstract());
std::set<Type*> KnownAbstractTypes;
Ty->PromoteAbstractToConcrete(&KnownAbstractTypes);
// If the type just became concrete, notify all users!
if (!Ty->isAbstract())