This commit completely rewrites Mapper::mapMetadata (the implementation
of llvm::MapMetadata) using an iterative algorithm. The guts of the new
algorithm are in MDNodeMapper::map, the entry function in a new class.
Previously, Mapper::mapMetadata performed a recursive exploration of the
graph with eager "just in case there's a reason" malloc traffic.
The new algorithm has these benefits:
- New nodes and temporaries are not created eagerly.
- Uniquing cycles are not duplicated (see new unit test).
- No recursion.
Given a node to map, it does this:
1. Use a worklist to perform a post-order traversal of the transitively
referenced unmapped nodes.
2. Track which nodes will change operands, and which will have new
addresses in the mapped scheme. Propagate the changes through the
POT until fixed point, to pick up uniquing cycles that need to
change.
3. Map all the distinct nodes without touching their operands. If
RF_MoveDistinctMetadata, they get mapped to themselves; otherwise,
they get mapped to clones.
4. Map the uniqued nodes (bottom-up), lazily creating temporaries for
forward references as needed.
5. Remap the operands of the distinct nodes.
Mehdi helped me out by profiling this with -flto=thin. On his workload
(importing/etc. for opt.cpp), MapMetadata sped up by 15%, contributed
about 50% less to persistent memory, and made about 100x fewer calls to
malloc. The speedup is less than I'd hoped. The profile mainly blames
DenseMap lookups; perhaps there's a way to reduce them (e.g., by
disallowing remapping of MDString).
It would be nice to break the strange remaining recursion on the Value
side: MapValue => materializeInitFor => RemapInstruction => MapValue. I
think we could do this by having materializeInitFor return a worklist of
things to be remapped.
llvm-svn: 265456
Remove a few old FIXMEs from the original commit of the Metadata/Value
split in r223802. These are commented out assertions to the effect that
calls between mapValue and mapMetadata never return nullptr.
(The only behaviour change is that Mapper::mapSimpleMetadata memoizes
the nullptr return.)
When I originally rewrote the mapping code, I thought we could be
stricter in the new metadata hierarchy and never return nullptr when
RF_NullMapMissingGlobalValues was off. It's still not entirely clear to
me why these assertions failed (a few months ago, I had a theory that I
forgot to write down, but that's helping no one).
Understood or not, I no longer see how these commented-out assertions
would be useful. I'm relegating them to the annals of source control
before making significant changes to ValueMapper.cpp.
llvm-svn: 265282
This adds an assertion to maintain the property from r265273. When
Mapper::mapSimpleMetadata calls Mapper::mapValue, it should not find its
way back to mapMetadataImpl. This guarantees that mapSimpleMetadata is
not involved in any recursion.
Since Mapper::mapValue calls out to arbitrary materializers, we need to
save a bit on the ValueMap to make this assertion effective.
There should be no functionality change here. This co-recursion should
already have been impossible.
llvm-svn: 265276
The main change is to delay materializing GlobalValue initializers from
Mapper::mapValue until Mapper::~Mapper. This effectively removes all
recursion from mapSimplifiedMetadata, as promised in r265270.
mapSimplifiedMetadata calls mapValue for ConstantAsMetadata nodes to
find the mapped constant, and now it shouldn't be possible for mapValue
to indirectly re-invoke mapMetadata. I'll add an assertion to that
effect in a follow-up (separated so that the assertion can easily be
reverted independently, if it comes to that).
This a step toward a broader goal: converting Mapper::mapMetadataImpl
from a recursive to an iterative algorithm.
When a BlockAddress points at a BasicBlock inside an unmaterialized
function body, we need to delay it until the function body is
materialized in Mapper::~Mapper. This commit creates a temporary
BasicBlock and returns a new BlockAddress, then RAUWs the BasicBlock
once it is known. This situation should be extremely rare since a
BlockAddress is usually used from within the function it's referencing
(and BlockAddress itself is rare).
There should be no observable functionality change.
llvm-svn: 265273
Split out a helper for mapping metadata without operands. This is any
metadata that is not an MDNode, and any MDNode where the answer is known
without looking at operands.
Through some weird twists, this function is co-recursive:
mapSimpleMetadata
=> MapValue
=> materializeInitFor
=> linkFunctionBody
=> RemapInstructions
=> MapMetadata
=> mapSimpleMetadata
I plan to break the recursion in a follow-up.
llvm-svn: 265270
Instead of checking live during MapMetadata whether a subprogram is
needed, seed the ValueMap with `nullptr` up-front.
There is a small hypothetical functionality change. Previously, calling
MapMetadataOp on a node whose "scope:" chain led to an unneeded
subprogram would return nullptr. However, if that were ever called,
then the subprogram would be needed; a situation that the IRMover is
supposed to avoid a priori!
Besides cleaning up the code a little, this restores a nice property:
MapMetadataOp returns the same as MapMetadata.
llvm-svn: 265229
Support seeding a ValueMap with nullptr for Metadata entries, a
situation I didn't consider in the Metadata/Value split.
I added a ValueMapper::getMappedMD accessor that returns an
Optional<Metadata*> with the mapped (possibly null) metadata. IRMover
needs to use this to avoid modifying the map when it's checking for
unneeded subprograms. I updated a call from bugpoint since I find the
new code clearer.
llvm-svn: 265228
Since we have moved to a model where functions are imported in bulk from
each source module after making summary-based importing decisions, there
is no longer a need to link metadata as a postpass, and all users have
been removed.
This essentially reverts r255909 and follow-on fixes.
llvm-svn: 264763
Address review feedback from r255909.
Move body of resolveCycles(bool AllowTemps) to
resolveRecursivelyImpl(bool AllowTemps). Revert resolveCycles back
to asserting on temps, and add new resolveNonTemporaries interface
to invoke the new implementation with AllowTemps=true. Document
the differences between these interfaces, specifically the effect
on RAUW support and uniquing. Call appropriate interface from
ValueMapper.
llvm-svn: 257389
As suggested in review for r255909, rename MDMaterialized to AllowTemps,
and identify the name of the boolean flag being set in calls to
saveMetadataList.
llvm-svn: 256653
Summary:
Third patch split out from http://reviews.llvm.org/D14752.
Only map in needed DISubroutine metadata (imported or otherwise linked
in functions and other DISubroutine referenced by inlined instructions).
This is supported for ThinLTO, LTO and llvm-link --only-needed, with
associated tests for each one.
Depends on D14838.
Reviewers: dexonsmith, joker.eph
Subscribers: davidxl, llvm-commits, joker.eph
Differential Revision: http://reviews.llvm.org/D14843
llvm-svn: 256003
Summary:
Second patch split out from http://reviews.llvm.org/D14752.
Maps metadata as a post-pass from each module when importing complete,
suturing up final metadata to the temporary metadata left on the
imported instructions.
This entails saving the mapping from bitcode value id to temporary
metadata in the importing pass, and from bitcode value id to final
metadata during the metadata linking postpass.
Depends on D14825.
Reviewers: dexonsmith, joker.eph
Subscribers: davidxl, llvm-commits, joker.eph
Differential Revision: http://reviews.llvm.org/D14838
llvm-svn: 255909
The difference is that now we don't error on out-of-comdat access to
internal global values. We copy them instead. This seems to match the
expectation of COFF linkers (see pr25686).
Original message:
Start deciding earlier what to link.
A traditional linker is roughly split in symbol resolution and
"copying
stuff".
The two tasks are badly mixed in lib/Linker.
This starts splitting them apart.
With this patch there are no direct call to linkGlobalValueBody or
linkGlobalValueProto. Everything is linked via WapValue.
This also includes a few fixes:
* A GV goes undefined if the comdat is dropped (comdat11.ll).
* We error if an internal GV goes undefined (comdat13.ll).
* We don't link an unused comdat.
The first two match the behavior of an ELF linker. The second one is
equivalent to running globaldce on the input.
llvm-svn: 254418
A traditional linker is roughly split in symbol resolution and "copying
stuff".
The two tasks are badly mixed in lib/Linker.
This starts splitting them apart.
With this patch there are no direct call to linkGlobalValueBody or
linkGlobalValueProto. Everything is linked via WapValue.
This also includes a few fixes:
* A GV goes undefined if the comdat is dropped (comdat11.ll).
* We error if an internal GV goes undefined (comdat13.ll).
* We don't link an unused comdat.
The first two match the behavior of an ELF linker. The second one is
equivalent to running globaldce on the input.
llvm-svn: 254336
Now the ValueMapper has two callbacks. The first one maps the
declaration. The ValueMapper records the mapping and then materializes
the body/initializer.
llvm-svn: 254209
Summary:
The patch to move metadata linking after global value linking didn't
correctly map unmaterialized global values to null as desired. They
were in fact mapped to the source copy. It largely worked by accident
since most module linker clients destroyed the source module which
caused the source GVs to be replaced by null, but caused a failure with
LTO linking on Windows:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20151109/312869.html
The problem is that a null return value from materializeValueFor is
handled by mapping the value to self. This is the desired behavior when
materializeValueFor is passed a non-GlobalValue. The problem is how to
distinguish that case from the case where we really do want to map to
null.
This patch addresses this by passing in a new flag to the value mapper
indicating that unmapped global values should be mapped to null. Other
Value types are handled as before.
Note that the documented behavior of asserting on unmapped values when
the flag RF_IgnoreMissingValues isn't set is currently disabled with
FIXME notes due to bootstrap failures. I modified these disabled asserts
so when they are eventually enabled again it won't assert for the
unmapped values when the new RF_NullMapMissingGlobalValues flag is set.
I also considered using a callback into the value materializer, but a
flag seemed cleaner given that there are already existing flags.
I also considered modifying materializeValueFor to return the input
value when we want to map to source and then treat a null return
to mean map to null. However, there are other value materializer
subclasses that implement materializeValueFor, and they would all need
to be audited and the return values possibly changed, which seemed
error-prone.
Reviewers: dexonsmith, joker.eph
Subscribers: pcc, llvm-commits
Differential Revision: http://reviews.llvm.org/D14682
llvm-svn: 253170
Gets a bit tricky in the ValueMapper, of course - not sure if we should
just expose a list of explicit types for each Value so that the
ValueMapper can be neutral to these special cases (it's OK for things
like load, where the explicit type is the result type - but when that's
not the case, it means plumbing through another "special" type... )
llvm-svn: 245728
As a follow-up to r244181, resolve uniquing cycles underneath distinct
nodes on the fly. This prevents uniquing cycles in early operands from
affecting later operands. It also removes an iteration through distinct
nodes' operands.
No real functional change here, just more prompt resolution of temporary
nodes.
llvm-svn: 244302
Rotate the algorithm for remapping distinct nodes in order to simplify
how uniquing cycles get resolved. This removes some of the recursion,
and, most importantly, exposes all uniquing cycles at the top-level.
Besides being a little more efficient -- temporary MDNodes won't live as
long -- the clearer logic should help protect against bugs like those
fixed in r243961 and r243976.
What are uniquing cycles? Why do they present challenges when remapping
metadata?
!0 = !{!1}
!1 = !{!0}
!0 and !1 form a simple uniquing cycle. When remapping from one
metadata graph to another, every uniquing cycle gets "duplicated"
through a dance:
!0-temp = !{!1?} ; map(!0): clone !0, VM[!0] = !0-temp
!1-temp = !{!0?} ; ..map(!1): clone !1, VM[!1] = !1-temp
!1-temp = !{!0-temp} ; ..map(!1): remap !1's operands
!2 = !{!0-temp} ; ..map(!1): uniquify: !1-temp => !2
!0-temp = !{!2} ; map(!0): remap !0's operands
!3 = !{!2} ; map(!0): uniquify: !0-temp => !3
; Result
!2 = !{!3}
!3 = !{!2}
(In the two "uniquify" steps above, the operands of !X-temp are compared
to the operands of !X. If they're the same, then !X-temp gets RAUW'ed
to !X; if they're different, then !X-temp is promoted to a new unique
node. The latter case always hits in for uniquing cycles, so we
duplicate all the nodes involved.)
Why is this a problem? Uniquable Metadata nodes that have temporary
node as transitive operands keep RAUW support until the temporary nodes
get finalized. With non-cycles, this happens automatically: when a
uniquable node's count of unresolved operands drops to zero, it
immediately sheds its own RAUW support (possibly triggering the same in
any node that references it). However, uniquing cycles create a
reference cycle, and uniqued nodes that transitively reference a
uniquing cycle are "stuck" in an unresolved state until someone calls
`MDNode::resolveCycles()` on a node in the unresolved subgraph.
Distinct nodes should help here (and mostly do): since they aren't
uniqued anywhere, they are guaranteed not to be RAUW'ed. They
effectively form a barrier between uniqued nodes, breaking some uniquing
cycles, and shielding uniqued nodes from uniquing cycles.
Unfortunately, with this barrier in place, the unresolved subgraph(s)
can be disjoint from the top-level node. The mapping algorithm needs to
find at least one representative from each disjoint subgraph. But which
nodes are *stuck*, and which will get resolved automatically? And which
nodes are in the unresolved subgraph? The old logic was conservative.
This commit rotates the logic for distinct nodes, so that we have access
to unresolved nodes at the top-level call to `llvm::MapMetadata()`.
Each time we return to the top-level, we know that all temporaries have
been RAUW'ed away. Here, it's safe (and necessary) to call
`resolveCycles()` immediately on unresolved operands.
This should also perform better than the old algorithm. The recursion
stack is shorter, temporary nodes don't live as long, and there are
fewer tracking references to unresolved nodes. As the debug info graph
introduces more 'distinct' nodes, remapping should incrementally get
cheaper and cheaper.
Aside from possible performance improvements (and reduced cruft in the
`LLVMContext`), there should be no functionality change here.
llvm-svn: 244181
Rename `remap()` to `remapOperands()`, and restrict its contract to
remapping operands. Previously, it also called `mapToMetadata()`, but
this logic is hard to reason about externally. In particular, this
refactors `mapUniquedNode()` to avoid redundant mapping calls, taking
advantage of the RAUWs that are already in place.
llvm-svn: 244168
r243883 and r243961 made a use-after-free far more likely:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/6041/steps/check-llvm%20asan/logs/stdio
Unresolved nodes get inserted into the `Cycles` array. If they later
get resolved through RAUW, we need to update the reference. It's
interesting that this never hit before (maybe an asan-ified clang
bootstrap with `-flto -g` would have hit it, but I admit I haven't tried
anything quite that crazy).
llvm-svn: 243976
r243883 started moving 'distinct' nodes instead of duplicated them in
lib/Linker. This had the side-effect of sometimes not cloning uniqued
nodes that reference them. I missed a corner case:
!named = !{!0}
!0 = !{!1}
!1 = distinct !{!0}
!0 is the entry point for "remapping", and a temporary clone (say,
!0-temp) is created and mapped in case we need to model a uniquing
cycle.
Recursive descent into !1. !1 is distinct, so we leave it alone,
but update its operand to !0-temp.
Pop back out to !0. Its only operand, !1, hasn't changed, so we don't
need to use !0-temp. !0-temp goes out of scope, and we're finished
remapping, but we're left with:
!named = !{!0}
!0 = !{!1}
!1 = distinct !{null} ; uh oh...
Previously, if !0 and !0-temp ended up with identical operands, then
!0-temp couldn't have been referenced at all. Now that distinct nodes
don't get duplicated, that assumption is invalid. We need to
!0-temp->replaceAllUsesWith(!0) before freeing !0-temp.
I found this while running an internal `-flto -g` bootstrap. Strangely,
there was no case of this in the open source bootstrap I'd done before
commit...
llvm-svn: 243961
Instead of cloning distinct `MDNode`s when linking in a module, just
move them over. The module linker destroys the source module, so the
old node would otherwise just be leaked on the context. Create the new
node in place. This also reduces the number of cloned uniqued nodes
(since it's less likely their operands have changed).
This mapping strategy is only correct when we're discarding the source,
so the linker turns it on via a ValueMapper flag, `RF_MoveDistinctMDs`.
There's nothing observable in terms of `llvm-link` output here: the
linked module should be semantically identical.
I'll be adding more 'distinct' nodes to the debug info metadata graph in
order to break uniquing cycles, so the benefits of this will partly come
in future commits. However, we should get some gains immediately, since
we have a fair number of 'distinct' `DILocation`s being linked in.
llvm-svn: 243883
This is a minor optimization to only check for unresolved operands
inside `mapDistinctNode()` if the operands have actually changed. This
shouldn't really cause any change in behaviour. I didn't actually see a
slowdown in a profile, I was just poking around nearby and saw the
opportunity.
llvm-svn: 243866
Alternatively, this type could be derived on-demand whenever
getResultElementType is called - if someone thinks that's the better
choice (simple time/space tradeoff), I'm happy to give it a go.
llvm-svn: 238716
(reverted in r235533)
Original commit message:
"Calls to llvm::Value::mutateType are becoming extra-sensitive now that
instructions have extra type information that will not be derived from
operands or result type (alloca, gep, load, call/invoke, etc... ). The
special-handling for mutateType will get more complicated as this work
continues - it might be worth making mutateType virtual & pushing the
complexity down into the classes that need special handling. But with
only two significant uses of mutateType (vectorization and linking) this
seems OK for now.
Totally open to ideas/suggestions/improvements, of course.
With this, and a bunch of exceptions, we can roundtrip an indirect call
site through bitcode and IR. (a direct call site is actually trickier...
I haven't figured out how to deal with the IR deserializer's lazy
construction of Function/GlobalVariable decl's based on the type of the
entity which means looking through the "pointer to T" type referring to
the global)"
The remapping done in ValueMapper for LTO was insufficient as the types
weren't correctly mapped (though I was using the post-mapped operands,
some of those operands might not have been mapped yet so the type
wouldn't be post-mapped yet). Instead use the pre-mapped type and
explicitly map all the types.
llvm-svn: 235651
This reverts commit r235458.
It looks like this might be breaking something LTO-ish. Looking into it
& will recommit with a fix/test case/etc once I've got more to go on.
llvm-svn: 235533
Calls to llvm::Value::mutateType are becoming extra-sensitive now that
instructions have extra type information that will not be derived from
operands or result type (alloca, gep, load, call/invoke, etc... ). The
special-handling for mutateType will get more complicated as this work
continues - it might be worth making mutateType virtual & pushing the
complexity down into the classes that need special handling. But with
only two significant uses of mutateType (vectorization and linking) this
seems OK for now.
Totally open to ideas/suggestions/improvements, of course.
With this, and a bunch of exceptions, we can roundtrip an indirect call
site through bitcode and IR. (a direct call site is actually trickier...
I haven't figured out how to deal with the IR deserializer's lazy
construction of Function/GlobalVariable decl's based on the type of the
entity which means looking through the "pointer to T" type referring to
the global)
llvm-svn: 235458
Allow unresolved nodes through the `MapMetadata()` if
`RF_NoModuleLevelChanges`, since there's no remapping to do anyway.
This fixes PR22929. I'll add a clang test as a follow-up.
llvm-svn: 232449
Track unresolved nodes under distinct `MDNode`s during `MapMetadata()`,
and resolve them at the end. Previously, these cycles wouldn't get
resolved.
llvm-svn: 228180
Now that the clone methods used by `MapMetadata()` don't do any
remapping (and return a temporary), they make more sense as member
functions on `MDNode` (and subclasses).
llvm-svn: 226541
As part of PR22235, introduce `DwarfNode` and `GenericDwarfNode`. The
former is a metadata node with a DWARF tag. The latter matches our
current (generic) schema of a header with string (and stringified
integer) data and an arbitrary number of operands.
This doesn't move it into place yet; that change will require a large
number of testcase updates.
llvm-svn: 226529
As pointed out in r226501, the distinction between `MDNode` and
`UniquableMDNode` is confusing. When we need subclasses of `MDNode`
that don't use all its functionality it might make sense to break it
apart again, but until then this makes the code clearer.
llvm-svn: 226520
Take advantage of the new ability of temporary nodes to mutate to
distinct and uniqued nodes to greatly simplify the `MapMetadata()`
helper functions.
llvm-svn: 226511
Change `MDTuple::getTemporary()` and `MDLocation::getTemporary()` to
return (effectively) `std::unique_ptr<T, MDNode::deleteTemporary>`, and
clean up call sites. (For now, `DIBuilder` call sites just call
`release()` immediately.)
There's an accompanying change in each of clang and polly to use the new
API.
llvm-svn: 226504
