| Commit message (Collapse) | Author | Age | Files | Lines |
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Update Builder and IRBuilder makeStructGet and makeStructSet functions
to require the memory order to be explicitly supplied. This is slightly
more verbose, but will reduce the chances that we forget to properly
consider synchronization when implementing new features in the future.
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GlobalStructInference optimizes gets of immutable fields of structs that
are only ever instantiated to initialize immutable globals. Due to all
the immutability, it's not possible for the optimized reads to
synchronize with any writes via the accessed memory, so we just need to
be careful to replace removed seqcst gets with seqcst fences.
As a drive-by, fix some stale comments in gsi.wast.
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Conservatively avoid introducing synchronization bugs by not optimizing
atomic struct.gets at all in GUFA. It is possible that we could be more
precise in the future.
Also remove obsolete logic dealing with the types of null values as a
drive-by. All null values now have bottom types, so the type mismatch
this code checked for is impossible.
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During function reconstruction, a walker iterates thru each instruction
of a function, incrementing a counter to find matching sequences. As a
result, the sequences of a function must be sorted by smallest start
index, otherwise reconstruction will miss outlining a repeat sequence.
I considered making a test for this commit, but the sort wasn't needed
until the tests started running on GitHub infra. I'm not sure what
specific architecture is causing the discrepancy in vector ordering, but
let's introduce the sort to be safe.
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GTO removes fields that are never read and also removes sets to those
fields. Update the pass to add a seqcst fence when removing a seqcst set
to preserve its effect on the global order of seqcst operations.
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Sequentially consistent gets that are optimized out need to have seqcst
fences inserted in their place to keep the same effect on global
ordering of sequentially consistent operations. In principle, acquire
gets could be similarly optimized with an acquire fence in their place,
but acquire fences synchronize more strongly than acquire gets, so this
may have a negative performance impact. For now, inhibit optimization of
acquire gets.
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Heap2Local replaces gets and sets of non-escaping heap allocations with
gets and sets of locals. Since the accessed data does not escape, it
cannot be used to directly synchronize with other threads, so this
optimization is generally safe even in the presence of shared structs
and atomic struct accesses. The only caveat is that sequentially
consistent accesses additionally participate in the global ordering of
sequentially consistent operations, and that effect on the global
ordering cannot be removed. Insert seqcst fences to maintain this global
synchronization when removing sequentially consistent gets and sets.
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Implement support for both sequentially consistent and acquire-release
variants of `struct.atomic.get` and `struct.atomic.set`, as proposed by
shared-everything-threads. Introduce a new `MemoryOrdering` enum for
describing different levels of atomicity (or the lack thereof). This new
enum should eventually be adopted by linear memory atomic accessors as
well to support acquire-release semantics, but for now just use it in
`StructGet` and `StructSet`.
In addition to implementing parsing and emitting for the instructions,
validate that shared-everything is enabled to use them, mark them as
having synchronization side effects, and lightly optimize them by
relaxing acquire-release accesses to non-shared structs to normal,
unordered accesses. This is valid because such accesses cannot possibly
synchronize with other threads. Also update Precompute to avoid
optimizing out synchronization points.
There are probably other passes that need to be updated to avoid
incorrectly optimizing synchronizing accesses, but identifying and
fixing them is left as future work.
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We normally like to move brs after ifs into the if, when in a loop:
(loop $loop
(if
..
(unreachable)
(code)
)
(br $loop)
)
=>
(loop $loop
(if
..
(unreachable)
(block
(code)
(br $loop) ;; moved in
)
)
)
However this may be invalid to do if the if condition is unreachable, as
then one arm may be concrete (`code` in the example could be an `i32`,
for example). As this is dead code anyhow, leave it for DCE.
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(#7138)
If we see a StructGet with no content (the type it reads from has no writes)
then we can make it unreachable. The old code literally just changed the type
to unreachable, which would later work out with refinalization - but only if
the StructGet's ref was unreachable. But it is possible for this situation to
occur without that, and if so, this hit the validation error "can't have an
unreachable node without an unreachable child".
To fix this, merge all code paths that handle "impossible" situations, which
simplifies things, and add this situation.
This uncovered an existing bug where we noted default values of refs, but
not non-refs (which could lead us to think that a field of a struct that only
was ever created by struct.new_default, was never created at all). Fixed as
well.
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LLVM recently split the bulk-memory-opt feature out from bulk-memory,
containing just memory.copy and memory.fill. This change follows that,
making bulk-memory-opt also enabled when all of bulk-memory is enabled.
It also introduces call-indirect-overlong following LLVM, but ignores
it, since Binaryen has always allowed the encoding (i.e. command
line flags enabling or disabling the feature are accepted but
ignored).
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This pass is now just part of Memory64Lowering.
Once this lands we can remove the `--table64-lowering` flag from
emscripten. Because I've used an alias here there will be some interim
period where emscripten will run this pass twice since it passed both
flags. However, this will only be temporary and that second run will be
a no-op since the first one will remove the feature.
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Move all state relevant to reading source maps out of WasmBinaryReader
and into a new utility, SourceMapReader. This is a prerequisite for
parallelizing the parsing of function bodies, since the source map
reader state is different at the beginning of each function.
Also take the opportunity to simplify the way we read source maps, for
example by deferring the reading of anything but the position of a debug
location until it will be used and by using `std::optional` instead of
singleton `std::set`s to store function prologue and epilogue debug
locations.
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RemoveUnusedBrs sinks blocks into If arms when those arms contain
branches to the blocks and the other arm and condition do not. Now that
we type Ifs with unreachable conditions as unreachable, it is possible
for the If arms to have a different type than the block that would be
sunk, so sinking the block would produce invalid IR. Fix the problem by
never sinking blocks into Ifs with unreachable conditions.
Fixes #7128.
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Previously the only Ifs that were typed unreachable were those in which
both arms were unreachable and those in which the condition was
unreachable that would have otherwise been typed none. This caused
problems in IRBuilder because Ifs with unreachable conditions and
value-returning arms would have concrete types, effectively hiding the
unreachable condition from the logic for dropping concretely typed
expressions preceding an unreachable expression when finishing a scope.
Relax the conditions under which an If can be typed unreachable so that
all Ifs with unreachable conditions or two unreachable arms are typed
unreachable. Propagating unreachability more eagerly this way makes
various optimizations of Ifs more powerful. It also requires new
handling for unreachable Ifs with concretely typed arms in the Printer
to ensure that printed wat remains valid.
Also update Unsubtyping, Flatten, and CodeFolding to account for the
newly unreachable Ifs.
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CodeFolding previously only worked on blocks that did not produce
values. It worked on Ifs that produced values, but only by accident; the
logic for folding matching tails was not written to support tails
producing concrete values, but it happened to work for Ifs because
subsequent ReFinalize runs fixed all the incorrect types it produced.
Improve the power of the optimization by explicitly handling tails that
produce concrete values for both blocks and ifs. Now that the core logic
handles concrete values correctly, remove the unnecessary ReFinalize
run.
Also remove the separate optimization of Ifs with identical arms; this
optimization requires ReFinalize and is already performed by
OptimizeInstructions.
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The LUB of sibling types is their common supertype, but after the
sibling types are merged, their LUB is the merged type, which is a
strict subtype of the previous LUB. This means that merging sibling
types causes `selects` to have stale types when the two select arms
previously had the two merged sibling types. To fix any potential stale
types, ReFinalize after merging sibling types.
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CodeFolding previously did not consider br_on_* instructions at all, so
it would happily merge tails even if there were br_on_* branches to the
same label with non-matching tails. Fix the bug by making any label
targeted by any instruction not explicitly handled by CodeFolding
unoptimizable. This will gracefully handle other branching instructions
like `resume` and `resume_throw` as well. Folding these branches
properly is left as future work.
Also rename the test file from code-folding_enable-threads.wast to just
code-folding.wast and enable all features instead of just threads. The
old name was left over from when the test was originally ported to lit,
and the new feature is necessary because the new test uses GC
instructions.
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Replacing an if with a select may have refined the type. Without this fix,
the sharper stale type checks complain.
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I forgot that there is a validation rule that the output type for
br_on_cast and br_on_cast_fail must be a subtype of the input type. We
were previously printing bottom input types in cases where the cast
operand was unreachable, but that's only valid if the cast type is the
same bottom type. Instead print the most precise valid input type, which
is the cast type itself.
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Since Load expressions use their `type` field to encode the type of the
loaded value, unreachable loads need to come up with some other valid
type to print. Previously we always chose i32 as that type, but that's
not valid when the load was originally a v128 load with an alignment of
8, since 8 is greater than the maximum valid alignment of 4 for an i32.
Fix the problem by taking alignment into account when choosing a type
for the unreachable load.
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br_on_cast and br_on_cast_fail have two type annotations: one for their
input type and one for their cast type. In cases where their operands
were unreachable, we were previously printing "unreachable" for the
input type annotation. This is not valid wat because "unreachable" is
not a reference type.
To fix the problem, print the bottom type of the cast type's hierarchy
as the input type for br_on_cast and br_on_cast_fail when the operand is
unreachable. This ensures that the instructions have the most precise
possible output type according to Wasm typing rules, so it maximizes the
number of contexts in which the printed instructions are valid.
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We previously allowed valid expressions to have stale types as long as
those stale types were supertypes of the most precise possible types for
the expressions. Allowing stale types like this could mask bugs where we
failed to propagate precise type information, though.
Make validation stricter by requiring all expressions except for control
flow structures to have the most precise possible types. Control flow
structures are exempt because many passes that can refine types wrap the
refined expressions in blocks with the old type to avoid the need for
refinalization. This pattern would be broken and we would need to
refinalize more frequently without this exception for control flow
structures.
Now that all non-control flow expressions must have precise types,
remove functionality relating to building select instructions with
non-precise types. Since finalization of selects now always calculates a
LUB rather than using a provided type, remove the type parameter from
BinaryenSelect in the C and JS APIs.
Now that stale types are no longer valid, fix a bug in TypeSSA where it
failed to refinalize module-level code. This bug previously would not
have caused problems on its own, but the stale types could cause
problems for later runs of Unsubtyping. Now the stale types would cause
TypeSSA output to fail validation.
Also fix a bug where Builder::replaceWithIdenticalType was in fact
replacing with refined types.
Fixes #7087.
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Before, we would simply not export a function that had an e.g. anyref
param. As a result, the modules were effectively "closed", which was
good for testing full closed-world mode, but not for testing degrees of
open world. To improve that, this PR allows the fuzzer to export such
functions, and an "enclose world" pass is added that "closes" the wasm
(makes it more compatible with closed-world) that is run 50% of the
time, giving us coverage of both styles.
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This pass lowers nontrapping FP to int instructions to implement LLVM's
conversion behavior.
This means that they are not fully complete lowerings according to the
wasm spec, but have the same
undefined behavior that LLM does. This keeps the pass simpler and
preserves existing behavior when
compiling without nontrapping-ft.
This will be used in emscripten, so that we can build libraries with
nontrapping-fp and lower them away after link if desired.
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Since IRBuilder already knows what labels are used by branches, it is
easy for it to pass that information when finalizing blocks. This avoids
finalization having to walk the blocks looking for branches, speeding up
a future version of the binary parser that uses IRBuilder by 10%.
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Since the resulting code has the same undefined behavior as LLVM, make
the pass name reflect that.
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IRBuilder contains a pointer to the current function that is used to
create scratch locals, look up the operand types for returns, etc. This
pointer is nullable because IRBuilder can also be used in non-function
contexts such as global initializers. Visiting the start of a function
sets the function pointer, and after this change visiting the end of a
function resets the pointer to null. This avoids potential problems
where code outside a function would be able to incorrectly use scratch
locals and returns if the IRBuilder had previously been used to build a
function.
This change requires some adjustments to Outlining, which visits code
out of order, so ends up visiting code from inside a function after
visiting the end of the function. To support this use case, add a
`setFunction` method to IRBuilder that lets the user explicitly control
its function context. Also remove the optional function pointer
parameter to the IRBuilder constructor since it is less flexible and not
used.
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When IRBuilder builds an empty non-block scope such as a function body,
an if arm, a try block, etc, it needs to produce some expression to
represent the empty contents. Previously it produced a nop, but change
it to produce an empty block instead. The binary writer and printer have
special logic to elide empty blocks, so this produces smaller output.
Update J2CLOpts to recognize functions containing empty blocks as
trivial to avoid regressing one of its tests.
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(#7072)
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There were previously two separate code paths for printing function
signatures, one for imported functions and one for declared functions.
The only intended difference was that parameter names were printed for
declared functions but not for imported functions.
Reduce duplication by consolidating the code paths, and add support for
printing names for imported function parameters that have them. Also fix
a bug where empty names were printed as `$` rather than the correct
`$""`.
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This pass lowers away memory.copy and memory.fill operations. It
generates a function that implements the each of the instructions and
replaces the instructions with calls to those functions.
It does not handle other bulk memory operations (e.g. passive segments
and table operations) because they are not used by emscripten to enable
targeting old browsers that don't support bulk memory.
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This PR fixes this situation:
(block $out
(local.set $x (struct.new X Y Z))
(struct.set $X 0 (local.get $x) (..br $out..)) ;; X' here has a br
)
(local.get $x)
=>
(block $out
(local.set $x (struct.new (..br $out..) Y Z))
)
(local.get $x)
We want to fold the struct.set into the struct.new, but the br is
a problem: if it executes then we skip the struct.set, and the last
local.get in fact reads the struct before the write. And, if we did this
optimization, we'd end up with the br on the struct.new, so it
would skip that instruction and even the local.set.
To fix this, we use the new API from #7039, which lets us query,
"is it ok to move the local.set to where the struct.set is?"
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I believe the history here is that
1. We added a PickLoadSigns pass. It checks if a load from memory is stored in
a local that is only every used in a signed or an unsigned manner. If it is, we can
adjust the sign of the load (load8_u/s) to do the sign/unsign during the load.
2. The pass finds each LocalGet and looks either 2 or 3 parents above it. For
a sign operation, we need to look up 3, since the operation is x << K >> K. For
an unsigned, we need only 2, since we have x & M. We hardcoded those
numbers 2 and 3.
3. We added the SignExt feature, which adds i32.extend8_s. This does a sign
extend with a single instruction, not two nested ones, so now we can sign-
extend at depth 2, unlike before. Properties::getSignExtValue was updated
for this, but not the pass PickLoadSigns.
The bug that is fixed here is that we looked at depth 3 for a sign-extend, and
we blindly accepted it if we found one. So we ended up accepting
(i32.extend8_s (ANYTHING (x))), which is a sign-extend of something, but
not of x, which is bad.
We were also missing an optimization opportunity, as we didn't look for
depth 2 sign extends.
This bug is quite old, from when Properties got SignExt support, in #3910.
But the blame isn't there - to notice this then, we'd have had to check each
caller of getSignExtValue throughout the codebase, which isn't reasonable.
The fault is mine, from the first write-up of PickLoadSigns in 2017: the code
should have been fully general, handling 2/3 and checking the output when
it does so (adding == curr, that the sign/zero-extended value is the one we
expect). That is what this PR does.
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See https://github.com/WebAssembly/memory64/pull/92
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When we combine a load/store offset with a const, we must not
overflow, as the semantics of offsets do not wrap.
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CFP is less precise than GUFA, in particular, when it flows around types then
it does not consider what field it is flowing them to, and its core data
structure is "if a struct.get is done on this type's field, what can be read?".
To see the issue this PR fixes, assume we have
A
/ \
B C
Then if we see struct.set $C, we know that can be read by a struct.get $A
(we can store a reference to a C in such a local/param/etc.), so we propagate
the value of that set to A. And, in general, anything in A can appear in B
(say, if we see a copy, a struct.set of struct.get that operates on types A,
then one of the sides might be a B), so we propagate from A to B. But
now we have propagated something from C to B, which might be of an
incompatible type.
This cannot cause runtime issues, as it just means we are propagating more
than we should, and will end up with less-useful results. But it can break
validation if no other value is possible but one with an incompatible type,
as we'd replace a struct.get $B with a value that only makes sense for C.
(The qualifier "no other value is possible" was added in the previous
sentence because if another one is possible then we'd end up with too
many values to infer anything, and not optimize at all, avoiding any error.)
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This fixes a regression from #7019. That PR fixed an error on situations with
mixed public and private types, but it made us stop optimizing in valid cases,
including cases with entirely private types.
The specific regression was that we checked if we had an entry in the
map of "can become immutable", and we thought that was enough. But
we may have a private child type with a public parent, and still be able to
optimize in the child if the field is not present in the parent. We also did
not have exhaustive checking of all the states canBecomeImmutable can be,
so add those + testing.
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This is NFC on 64-bit systems but noticeable on 32.
Also remove the 32-bit path in hash_combine. That isn't necessary for this fix,
but it makes the code simpler and also makes debugging between systems
simpler. It might also avoid problems in future cases, if we are lucky. The only
cost is perhaps a slight slowdown on 32-bit systems, which seems worth it.
Fixes #7046
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unrefine the output (#7036)
Paradoxically, when a BrOn's castType is refined, its own type (the type it flows out)
can get un-refined: making the castType non-nullable means nulls no longer
flow on the branch, so they may flow out directly, making the BrOn nullable.
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TypeMerging works by representing the type definition graph as a
partitioned DFA and then refining the partitions to find mergeable
types. #7023 was due to a bug where the DFA included edges from public
types to their children, but did not necessarily include corresponding
states for those children.
One way to fix the bug would have been to traverse the type graph,
finding all reachable public types and creating DFA states for them, but
that might be expensive in cases where there are large graphs of public
types.
Instead, fix the problem by removing the edges from public types to
their children entirely. Types reachable from public types are also
public and therefore are not eligible to be merged, so these edges were
never necessary for correctness.
Fixes #7023.
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We only checked for the case of the immediate super being public while we
are private, but it might be a grandsuper instead. That is, any ancestor that
is public will prevent GTO from removing a field (since we can only add
fields on top of our ancestors). Also, the ancestors might not all have the
field, which would add more complexity to that particular assertion, so just
remove it, and add comprehensive tests.
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These were added to avoid common problems with closed world mode, but
in practice they are causing more harm than good, forcing users to work
around them. In the meantime (until #6965), remove this validation to unblock
current toolchain makers.
Fix GlobalTypeOptimization and AbstractTypeRefining on issues that this
uncovers: without this validation, it is possible to run them on more wasm
files than before, hence these were not previously detected. They are
bundled in this PR because their tests cannot validate before this PR.
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Similar to #7017 . As with that PR, this reduces some optimizations that were
valid, as we tried to do something complex here and refine types in a public
rec group when it seemed safe to do so, but our analysis was incomplete.
The testcase here shows how another operation can end up causing a
dependency that breaks things, if another type that uses one that we
modify is public. To be safe, ignore all public types. In the future perhaps we
can find a good way to handle "almost-private" types in public rec groups,
in closed world.
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Similar to #7017 and #7018
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TypeUpdater which it uses internally already does so, but we must also
ignore such types earlier, and make no other modifications to them.
Helps #7015
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