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dad20b2ae2
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.)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223802 91177308-0d34-0410-b5e6-96231b3b80d8
100 lines
3.2 KiB
C++
100 lines
3.2 KiB
C++
//===- llvm/IR/MetadataTracking.h - Metadata tracking ---------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Low-level functions to enable tracking of metadata that could RAUW.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_IR_METADATATRACKING_H
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#define LLVM_IR_METADATATRACKING_H
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#include "llvm/ADT/PointerUnion.h"
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#include "llvm/Support/Casting.h"
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#include <type_traits>
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namespace llvm {
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class Metadata;
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class MetadataAsValue;
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/// \brief API for tracking metadata references through RAUW and deletion.
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///
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/// Shared API for updating \a Metadata pointers in subclasses that support
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/// RAUW.
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///
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/// This API is not meant to be used directly. See \a TrackingMDRef for a
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/// user-friendly tracking reference.
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class MetadataTracking {
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public:
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/// \brief Track the reference to metadata.
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///
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/// Register \c MD with \c *MD, if the subclass supports tracking. If \c *MD
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/// gets RAUW'ed, \c MD will be updated to the new address. If \c *MD gets
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/// deleted, \c MD will be set to \c nullptr.
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///
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/// If tracking isn't supported, \c *MD will not change.
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///
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/// \return true iff tracking is supported by \c MD.
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static bool track(Metadata *&MD) {
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return track(&MD, *MD, static_cast<Metadata *>(nullptr));
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}
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/// \brief Track the reference to metadata for \a Metadata.
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///
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/// As \a track(Metadata*&), but with support for calling back to \c Owner to
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/// tell it that its operand changed. This could trigger \c Owner being
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/// re-uniqued.
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static bool track(void *Ref, Metadata &MD, Metadata &Owner) {
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return track(Ref, MD, &Owner);
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}
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/// \brief Track the reference to metadata for \a MetadataAsValue.
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///
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/// As \a track(Metadata*&), but with support for calling back to \c Owner to
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/// tell it that its operand changed. This could trigger \c Owner being
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/// re-uniqued.
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static bool track(void *Ref, Metadata &MD, MetadataAsValue &Owner) {
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return track(Ref, MD, &Owner);
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}
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/// \brief Stop tracking a reference to metadata.
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///
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/// Stops \c *MD from tracking \c MD.
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static void untrack(Metadata *&MD) { untrack(&MD, *MD); }
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static void untrack(void *Ref, Metadata &MD);
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/// \brief Move tracking from one reference to another.
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///
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/// Semantically equivalent to \c untrack(MD) followed by \c track(New),
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/// except that ownership callbacks are maintained.
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///
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/// Note: it is an error if \c *MD does not equal \c New.
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///
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/// \return true iff tracking is supported by \c MD.
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static bool retrack(Metadata *&MD, Metadata *&New) {
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return retrack(&MD, *MD, &New);
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}
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static bool retrack(void *Ref, Metadata &MD, void *New);
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/// \brief Check whether metadata is replaceable.
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static bool isReplaceable(const Metadata &MD);
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typedef PointerUnion<MetadataAsValue *, Metadata *> OwnerTy;
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private:
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/// \brief Track a reference to metadata for an owner.
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///
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/// Generalized version of tracking.
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static bool track(void *Ref, Metadata &MD, OwnerTy Owner);
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};
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} // end namespace llvm
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#endif
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