IR: Split Metadata from Value
Split `Metadata` away from the `Value` class hierarchy, as part of
PR21532. Assembly and bitcode changes are in the wings, but this is the
bulk of the change for the IR C++ API.
I have a follow-up patch prepared for `clang`. If this breaks other
sub-projects, I apologize in advance :(. Help me compile it on Darwin
I'll try to fix it. FWIW, the errors should be easy to fix, so it may
be simpler to just fix it yourself.
This breaks the build for all metadata-related code that's out-of-tree.
Rest assured the transition is mechanical and the compiler should catch
almost all of the problems.
Here's a quick guide for updating your code:
- `Metadata` is the root of a class hierarchy with three main classes:
`MDNode`, `MDString`, and `ValueAsMetadata`. It is distinct from
the `Value` class hierarchy. It is typeless -- i.e., instances do
*not* have a `Type`.
- `MDNode`'s operands are all `Metadata *` (instead of `Value *`).
- `TrackingVH<MDNode>` and `WeakVH` referring to metadata can be
replaced with `TrackingMDNodeRef` and `TrackingMDRef`, respectively.
If you're referring solely to resolved `MDNode`s -- post graph
construction -- just use `MDNode*`.
- `MDNode` (and the rest of `Metadata`) have only limited support for
`replaceAllUsesWith()`.
As long as an `MDNode` is pointing at a forward declaration -- the
result of `MDNode::getTemporary()` -- it maintains a side map of its
uses and can RAUW itself. Once the forward declarations are fully
resolved RAUW support is dropped on the ground. This means that
uniquing collisions on changing operands cause nodes to become
"distinct". (This already happened fairly commonly, whenever an
operand went to null.)
If you're constructing complex (non self-reference) `MDNode` cycles,
you need to call `MDNode::resolveCycles()` on each node (or on a
top-level node that somehow references all of the nodes). Also,
don't do that. Metadata cycles (and the RAUW machinery needed to
construct them) are expensive.
- An `MDNode` can only refer to a `Constant` through a bridge called
`ConstantAsMetadata` (one of the subclasses of `ValueAsMetadata`).
As a side effect, accessing an operand of an `MDNode` that is known
to be, e.g., `ConstantInt`, takes three steps: first, cast from
`Metadata` to `ConstantAsMetadata`; second, extract the `Constant`;
third, cast down to `ConstantInt`.
The eventual goal is to introduce `MDInt`/`MDFloat`/etc. and have
metadata schema owners transition away from using `Constant`s when
the type isn't important (and they don't care about referring to
`GlobalValue`s).
In the meantime, I've added transitional API to the `mdconst`
namespace that matches semantics with the old code, in order to
avoid adding the error-prone three-step equivalent to every call
site. If your old code was:
MDNode *N = foo();
bar(isa <ConstantInt>(N->getOperand(0)));
baz(cast <ConstantInt>(N->getOperand(1)));
bak(cast_or_null <ConstantInt>(N->getOperand(2)));
bat(dyn_cast <ConstantInt>(N->getOperand(3)));
bay(dyn_cast_or_null<ConstantInt>(N->getOperand(4)));
you can trivially match its semantics with:
MDNode *N = foo();
bar(mdconst::hasa <ConstantInt>(N->getOperand(0)));
baz(mdconst::extract <ConstantInt>(N->getOperand(1)));
bak(mdconst::extract_or_null <ConstantInt>(N->getOperand(2)));
bat(mdconst::dyn_extract <ConstantInt>(N->getOperand(3)));
bay(mdconst::dyn_extract_or_null<ConstantInt>(N->getOperand(4)));
and when you transition your metadata schema to `MDInt`:
MDNode *N = foo();
bar(isa <MDInt>(N->getOperand(0)));
baz(cast <MDInt>(N->getOperand(1)));
bak(cast_or_null <MDInt>(N->getOperand(2)));
bat(dyn_cast <MDInt>(N->getOperand(3)));
bay(dyn_cast_or_null<MDInt>(N->getOperand(4)));
- A `CallInst` -- specifically, intrinsic instructions -- can refer to
metadata through a bridge called `MetadataAsValue`. This is a
subclass of `Value` where `getType()->isMetadataTy()`.
`MetadataAsValue` is the *only* class that can legally refer to a
`LocalAsMetadata`, which is a bridged form of non-`Constant` values
like `Argument` and `Instruction`. It can also refer to any other
`Metadata` subclass.
(I'll break all your testcases in a follow-up commit, when I propagate
this change to assembly.)
llvm-svn: 223802
diff --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index 33b9ed2..d790f9e 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -44,9 +44,8 @@
}
Value::Value(Type *ty, unsigned scid)
- : VTy(checkType(ty)), UseList(nullptr), Name(nullptr), SubclassID(scid),
- HasValueHandle(0), SubclassOptionalData(0), SubclassData(0),
- NumOperands(0) {
+ : VTy(checkType(ty)), UseList(nullptr), SubclassID(scid), HasValueHandle(0),
+ SubclassOptionalData(0), SubclassData(0), NumOperands(0) {
// FIXME: Why isn't this in the subclass gunk??
// Note, we cannot call isa<CallInst> before the CallInst has been
// constructed.
@@ -63,6 +62,8 @@
// Notify all ValueHandles (if present) that this value is going away.
if (HasValueHandle)
ValueHandleBase::ValueIsDeleted(this);
+ if (isUsedByMetadata())
+ ValueAsMetadata::handleDeletion(this);
#ifndef NDEBUG // Only in -g mode...
// Check to make sure that there are no uses of this value that are still
@@ -82,13 +83,19 @@
// If this value is named, destroy the name. This should not be in a symtab
// at this point.
- if (Name && SubclassID != MDStringVal)
- Name->Destroy();
+ destroyValueName();
// There should be no uses of this object anymore, remove it.
LeakDetector::removeGarbageObject(this);
}
+void Value::destroyValueName() {
+ ValueName *Name = getValueName();
+ if (Name)
+ Name->Destroy();
+ setValueName(nullptr);
+}
+
bool Value::hasNUses(unsigned N) const {
const_use_iterator UI = use_begin(), E = use_end();
@@ -146,9 +153,7 @@
} else if (Argument *A = dyn_cast<Argument>(V)) {
if (Function *P = A->getParent())
ST = &P->getValueSymbolTable();
- } else if (isa<MDString>(V))
- return true;
- else {
+ } else {
assert(isa<Constant>(V) && "Unknown value type!");
return true; // no name is setable for this.
}
@@ -159,14 +164,12 @@
// Make sure the empty string is still a C string. For historical reasons,
// some clients want to call .data() on the result and expect it to be null
// terminated.
- if (!Name) return StringRef("", 0);
- return Name->getKey();
+ if (!getValueName())
+ return StringRef("", 0);
+ return getValueName()->getKey();
}
void Value::setName(const Twine &NewName) {
- assert(SubclassID != MDStringVal &&
- "Cannot set the name of MDString with this method!");
-
// Fast path for common IRBuilder case of setName("") when there is no name.
if (NewName.isTriviallyEmpty() && !hasName())
return;
@@ -193,20 +196,17 @@
if (!ST) { // No symbol table to update? Just do the change.
if (NameRef.empty()) {
// Free the name for this value.
- Name->Destroy();
- Name = nullptr;
+ destroyValueName();
return;
}
- if (Name)
- Name->Destroy();
-
// NOTE: Could optimize for the case the name is shrinking to not deallocate
// then reallocated.
+ destroyValueName();
// Create the new name.
- Name = ValueName::Create(NameRef);
- Name->setValue(this);
+ setValueName(ValueName::Create(NameRef));
+ getValueName()->setValue(this);
return;
}
@@ -214,21 +214,18 @@
// then reallocated.
if (hasName()) {
// Remove old name.
- ST->removeValueName(Name);
- Name->Destroy();
- Name = nullptr;
+ ST->removeValueName(getValueName());
+ destroyValueName();
if (NameRef.empty())
return;
}
// Name is changing to something new.
- Name = ST->createValueName(NameRef, this);
+ setValueName(ST->createValueName(NameRef, this));
}
void Value::takeName(Value *V) {
- assert(SubclassID != MDStringVal && "Cannot take the name of an MDString!");
-
ValueSymbolTable *ST = nullptr;
// If this value has a name, drop it.
if (hasName()) {
@@ -242,9 +239,8 @@
// Remove old name.
if (ST)
- ST->removeValueName(Name);
- Name->Destroy();
- Name = nullptr;
+ ST->removeValueName(getValueName());
+ destroyValueName();
}
// Now we know that this has no name.
@@ -270,9 +266,9 @@
// This works even if both values have no symtab yet.
if (ST == VST) {
// Take the name!
- Name = V->Name;
- V->Name = nullptr;
- Name->setValue(this);
+ setValueName(V->getValueName());
+ V->setValueName(nullptr);
+ getValueName()->setValue(this);
return;
}
@@ -280,10 +276,10 @@
// then reinsert it into ST.
if (VST)
- VST->removeValueName(V->Name);
- Name = V->Name;
- V->Name = nullptr;
- Name->setValue(this);
+ VST->removeValueName(V->getValueName());
+ setValueName(V->getValueName());
+ V->setValueName(nullptr);
+ getValueName()->setValue(this);
if (ST)
ST->reinsertValue(this);
@@ -334,6 +330,8 @@
// Notify all ValueHandles (if present) that this value is going away.
if (HasValueHandle)
ValueHandleBase::ValueIsRAUWd(this, New);
+ if (isUsedByMetadata())
+ ValueAsMetadata::handleRAUW(this, New);
while (!use_empty()) {
Use &U = *UseList;