D97247 added the reverse mapping from unwind destination to their
source, but it had a critical bug; sources can be multiple, because
multiple BBs can have a single BB as their unwind destination.
This changes `WasmEHFuncInfo::getUnwindSrc` to `getUnwindSrcs` and makes
it return a vector rather than a single BB. It does not return the const
reference to the existing vector but creates a new vector because
`WasmEHFuncInfo` stores not `BasicBlock*` or `MachineBasicBlock*` but
`PointerUnion` of them. Also I hoped to unify those methods for
`BasicBlock` and `MachineBasicBlock` into one using templates to reduce
duplication, but failed because various usages require `BasicBlock*` to
be `const` but it's hard to make it `const` for `MachineBasicBlock`
usages.
Fixes https://github.com/emscripten-core/emscripten/issues/13514.
(More precisely, fixes
https://github.com/emscripten-core/emscripten/issues/13514#issuecomment-784708744)
Reviewed By: dschuff, tlively
Differential Revision: https://reviews.llvm.org/D97583
This CL is not big but contains changes that span multiple analyses and
passes. This description is very long because it tries to explain basics
on what each pass/analysis does and why we need this change on top of
that. Please feel free to skip parts that are not necessary for your
understanding.
---
`WasmEHFuncInfo` contains the mapping of <EH pad, the EH pad's next
unwind destination>. The value (unwind dest) here is where an exception
should end up when it is not caught by the key (EH pad). We record this
info in WasmEHPrepare to fix catch mismatches, because the CFG itself
does not have this info. A CFG only contains BBs and
predecessor-successor relationship between them, but in `WasmEHFuncInfo`
the unwind destination BB is not necessarily a successor or the key EH
pad BB. Their relationship can be intuitively explained by this C++ code
snippet:
```
try {
try {
foo();
} catch (int) { // EH pad
...
}
} catch (...) { // unwind destination
}
```
So when `foo()` throws, it goes to `catch (int)` first. But if it is not
caught by it, it ends up in the next unwind destination `catch (...)`.
This unwind destination is what you see in `catchswitch`'s
`unwind label %bb` part.
---
`WebAssemblyExceptionInfo` groups exceptions so that they can be sorted
continuously together in CFGSort, as we do for loops. What this analysis
does is very simple: it creates a single `WebAssemblyException` per EH
pad, and all BBs that are dominated by that EH pad are included in this
exception. We also identify subexception relationship in this way: if
EHPad A domiantes EHPad B, EHPad B's exception is a subexception of
EHPad A's exception.
This simple rule turns out to be incorrect in some cases. In
`WasmEHFuncInfo`, if EHPad A's unwind destination is EHPad B, it means
semantically EHPad B should not be included in EHPad A's exception,
because it does not make sense to rethrow/delegate to an inner scope.
This is what happened in CFGStackify as a result of this:
```
try
try
catch
... <- %dest_bb is among here!
end
delegate %dest_bb
```
So this patch adds a phase in `WebAssemblyExceptionInfo::recalculate` to
make sure excptions' unwind destinations are not subexceptions of
their unwind sources in `WasmEHFuncInfo`.
But this alone does not prevent `dest_bb` in the example above from
being sorted within the inner `catch`'s exception, even if its exception
is not a subexception of that `catch`'s exception anymore, because of
how CFGSort works, which will be explained below.
---
CFGSort places BBs within the same `SortRegion` (loop or exception)
continuously together so they can be demarcated with `loop`-`end_loop`
or `catch`-`end_try` in CFGStackify.
`SortRegion` is a wrapper for one of `MachineLoop` or
`WebAssemblyException`. `SortRegionInfo` already does some complicated
things because there discrepancies between those two data structures.
`WebAssemblyException` is what we control, and it is defined as an EH
pad as its header and BBs dominated by the header as its BBs (with a
newly added exception of unwind destinations explained in the previous
paragraph). But `MachineLoop` is an LLVM data structure and uses the
standard loop detection algorithm. So by the algorithm, BBs that are 1.
dominated by the loop header and 2. have a path back to its header.
Because of the second condition, many BBs that are dominated by the loop
header are not included in the loop. So BBs that contain `return` or
branches to outside of the loop are not technically included in
`MachineLoop`, but they can be sorted together with the loop with no
problem.
Maybe to relax the condition, in CFGSort, when we are in a `SortRegion`
we allow sorting of not only BBs that belong to the current innermost
region but also BBs that are by the current region header.
(This was written this way from the first version written by Dan, when
only loops existed.) But now, we have cases in exceptions when EHPad B
is the unwind destination for EHPad A, even if EHPad B is dominated by
EHPad A it should not be included in EHPad A's exception, and should not
be sorted within EHPad A.
One way to make things work, at least correctly, is change `dominates`
condition to `contains` condition for `SortRegion` when sorting BBs, but
this will change compilation results for existing non-EH code and I
can't be sure it will not degrade performance or code size. I think it
will degrade performance because it will force many BBs dominated by a
loop, which don't have the path back to the header, to be placed after
the loop and it will likely to create more branches and blocks.
So this does a little hacky check when adding BBs to `Preferred` list:
(`Preferred` list is a ready list. CFGSort maintains ready list in two
priority queues: `Preferred` and `Ready`. I'm not very sure why, but it
was written that way from the beginning. BBs are first added to
`Preferred` list and then some of them are pushed to `Ready` list, so
here we only need to guard condition for `Preferred` list.)
When adding a BB to `Preferred` list, we check if that BB is an unwind
destination of another BB. To do this, this adds the reverse mapping,
`UnwindDestToSrc`, and getter methods to `WasmEHFuncInfo`. And if the BB
is an unwind destination, it checks if the current stack of regions
(`Entries`) contains its source BB by traversing the stack backwards. If
we find its unwind source in there, we add the BB to its `Deferred`
list, to make sure that unwind destination BB is added to `Preferred`
list only after that region with the unwind source BB is sorted and
popped from the stack.
---
This does not contain a new test that crashes because of this bug, but
this fix changes the result for one of existing test case. This test
case didn't crash because it fortunately didn't contain `delegate` to
the incorrectly placed unwind destination BB.
Fixes https://github.com/emscripten-core/emscripten/issues/13514.
Reviewed By: dschuff, tlively
Differential Revision: https://reviews.llvm.org/D97247
When it was first created, CFGSort only made sure BBs in each
`MachineLoop` are sorted together. After we added exception support,
CFGSort now also sorts BBs in each `WebAssemblyException`, which
represents a `catch` block, together, and
`Region` class was introduced to be a thin wrapper for both
`MachineLoop` and `WebAssemblyException`.
But how we compute those loops and exceptions is different.
`MachineLoopInfo` is constructed using the standard loop computation
algorithm in LLVM; the definition of loop is "a set of BBs that are
dominated by a loop header and have a path back to the loop header". So
even if some BBs are semantically contained by a loop in the original
program, or in other words dominated by a loop header, if they don't
have a path back to the loop header, they are not considered a part of
the loop. For example, if a BB is dominated by a loop header but
contains `call abort()` or `rethrow`, it wouldn't have a path back to
the header, so it is not included in the loop.
But `WebAssemblyException` is wasm-specific data structure, and its
algorithm is simple: a `WebAssemblyException` consists of an EH pad and
all BBs dominated by the EH pad. So this scenario is possible: (This is
also the situation in the newly added test in cfg-stackify-eh.ll)
```
Loop L: header, A, ehpad, latch
Exception E: ehpad, latch, B
```
(B contains `abort()`, so it does not have a path back to the loop
header, so it is not included in L.)
And it is sorted in this order:
```
header
A
ehpad
latch
B
```
And when CFGStackify places `end_loop` or `end_try` markers, it
previously used `WebAssembly::getBottom()`, which returns the latest BB
in the sorted order, and placed the marker there. So in this case the
marker placements will be like this:
```
loop
header
try
A
catch
ehpad
latch
end_loop <-- misplaced!
B
end_try
```
in which nesting between the loop and the exception is not correct.
`end_loop` marker has to be placed after `B`, and also after `end_try`.
Maybe the fundamental way to solve this problem is to come up with our
own algorithm for computing loop region too, in which we include all BBs
dominated by a loop header in a loop. But this takes a lot more effort.
The only thing we need to fix is actually, `getBottom()`. If we make it
return the right BB, which means in case of a loop, the latest BB of the
loop itself and all exceptions contained in there, we are good.
This renames `Region` and `RegionInfo` to `SortRegion` and
`SortRegionInfo` and extracts them into their own file. And add
`getBottom` to `SortRegionInfo` class, from which it can access
`WebAssemblyExceptionInfo`, so that it can compute a correct bottom
block for loops.
Reviewed By: dschuff
Differential Revision: https://reviews.llvm.org/D84724
Previously, it tried to infer the correct destination block from the
successor list, but this is a rather tricky propspect, given the
existence of successors that occur mid-block, such as invoke, and
potentially in the future, callbr/INLINEASM_BR. (INLINEASM_BR, in
particular would be problematic, because its successor blocks are not
distinct from "normal" successors, as EHPads are.)
Instead, require the caller to pass in the expected fallthrough
successor explicitly. In most callers, the correct block is
immediately clear. But, in MachineBlockPlacement, we do need to record
the original ordering, before starting to reorder blocks.
Unfortunately, the goal of decoupling the behavior of end-of-block
jumps from the successor list has not been fully accomplished in this
patch, as there is currently no other way to determine whether a block
is intended to fall-through, or end as unreachable. Further work is
needed there.
Differential Revision: https://reviews.llvm.org/D79605
Summary:
The previous code for determining the innermost region in CFGSort was
not correct. We determine subregion relationship by domination of their
headers, i.e., if region A's header dominates region B's header, B is a
subregion of A. Previously we assumed that if a BB belongs to both a
loop and an exception, the region with fewer number of BBs is the
innermost one. This may not be true, because while WebAssemblyException
contains BBs in all its subregions (loops or exceptions), MachineLoop
may not, because MachineLoop does not contain BBs that don't have a path
to its header even if they are dominated by its header.
Loop header <---|
| |
Exception header |
| \ |
A B |
| \ |
| C |
| |
Loop latch |
| |
-------------|
For example, in this CFG, the loop does not contain B and C, because
they don't have a path back to the loops header. But for CFGSort we
consider the exception here belongs to the loop and the exception should
be a subregion of the loop and scheduled together.
So here we should use `WE->contains(ML->getHeader())` (but not
`ML->contains(WE->getHeader())`, for the stated region above).
This also fixes some comments and deletes `Regions` vector in
`RegionInfo` class, which was not used anywere.
Reviewers: dschuff
Subscribers: sbc100, jgravelle-google, hiraditya, sunfish, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D77181
These names have been changed from CamelCase to camelCase, but there were
many places (comments mostly) that still used the old names.
This change is NFC.
Summary:
In CFGSort, we try to make EH pads have higher priorities as soon as
they are ready to be sorted, to prevent creation of unwind destination
mismatches in CFGStackify. We did that by making priority queues'
comparison function prefer EH pads, but it was possible for an EH pad
to be popped from `Preferred` queue and then not sorted immediately and
enter `Ready` queue instead in a certain condition. This patch makes
sure that special condition does not consider EH pads as its candidates.
Reviewers: dschuff
Subscribers: sbc100, jgravelle-google, hiraditya, sunfish, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68229
llvm-svn: 373302
Now that we've moved to C++14, we no longer need the llvm::make_unique
implementation from STLExtras.h. This patch is a mechanical replacement
of (hopefully) all the llvm::make_unique instances across the monorepo.
llvm-svn: 369013
Summary:
`WebAssembly::analyzeBranch` now does not analyze anything if the
function is CFG stackified. We were previously doing similar things by
checking if a branch's operand is whether an integer or an MBB, but this
failed to bail out when a BB did not have any terminators.
Consider this case:
```
bb0:
try $label0
call @foo // unwinds to %ehpad
bb1:
...
br $label0 // jumps to %cont. can be deleted
ehpad:
catch
...
cont:
end_try
```
Here `br $label0` will be deleted in CFGStackify's
`removeUnnecessaryInstrs` function, because we jump to the %cont block
even without the branch. But in this case, MachineVerifier fails to
verify this, because `ehpad` is not a successor of `bb1` even if `bb1`
does not have any terminators. MachineVerifier incorrectly thinks `bb1`
falls through to the next block.
This pass now consistently rejects all analysis after CFGStackify
whether a BB has terminators or not, also making the MachineVerifier
work. (MachineVerifier does not try to verify relationships between BBs
if `analyzeBranch` fails, the behavior we want after CFGStackify.)
This also adds a new option `-wasm-disable-ehpad-sort` for testing. This
option helps create the sorted order we want to test, and without the
fix in this patch, the tests in cfg-stackify-eh.ll fail at
MachineVerifier with `-wasm-disable-ehpad-sort`.
Reviewers: dschuff
Subscribers: sunfish, sbc100, jgravelle-google, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D59740
llvm-svn: 357015
Class `RegionInfo` was `SortUnitInfo` before, so the variables were
named `SUI`. Now the class name is `RegionInfo`, so this renames `SUI`
to `RI`, matching the class name.
llvm-svn: 356861
Summary:
This patch fixes clang-tidy warnings on wasm-only files.
The list of checks used is:
`-*,clang-diagnostic-*,llvm-*,misc-*,-misc-unused-parameters,readability-identifier-naming,modernize-*`
(LLVM's default .clang-tidy list is the same except it does not have
`modernize-*`. But I've seen in multiple CLs in LLVM the modernize style
was recommended and code was fixed based on the style, so I added it as
well.)
The common fixes are:
- Variable names start with an uppercase letter
- Function names start with a lowercase letter
- Use `auto` when you use casts so the type is evident
- Use inline initialization for class member variables
- Use `= default` for empty constructors / destructors
- Use `using` in place of `typedef`
Reviewers: sbc100, tlively, aardappel
Subscribers: dschuff, sunfish, jgravelle-google, yurydelendik, kripken, MatzeB, mgorny, rupprecht, llvm-commits
Differential Revision: https://reviews.llvm.org/D57500
llvm-svn: 353075
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
Summary:
gcc does not like
const Region *Region;
It wants a different name for the variable.
Is there a better convention for what name to use in such a case?
Reviewers: sbc100, aheejin
Subscribers: aheejin, jgravelle-google, dschuff, llvm-commits
Differential Revision: https://reviews.llvm.org/D50472
Patch by Alon Zakai (kripken)
llvm-svn: 339398
Summary:
This patch extends CFGSort pass to support exception handling. Once it
places a loop header, it does not place blocks that are not dominated by
the loop header until all the loop blocks are sorted. This patch extends
the same algorithm to exception 'catch' part, using the information
calculated by WebAssemblyExceptionInfo class.
Reviewers: dschuff, sunfish
Subscribers: sbc100, jgravelle-google, llvm-commits
Differential Revision: https://reviews.llvm.org/D46500
llvm-svn: 339172
Summary:
Added more utility functions that will be used in EH-related passes Also
changed `LoopBottom` function to `getBottom` and uses templates to be
able to handle other classes as well, which will be used in CFGSort
later.
Reviewers: dschuff
Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits
Differential Revision: https://reviews.llvm.org/D48262
llvm-svn: 335006
The DEBUG() macro is very generic so it might clash with other projects.
The renaming was done as follows:
- git grep -l 'DEBUG' | xargs sed -i 's/\bDEBUG\s\?(/LLVM_DEBUG(/g'
- git diff -U0 master | ../clang/tools/clang-format/clang-format-diff.py -i -p1 -style LLVM
- Manual change to APInt
- Manually chage DOCS as regex doesn't match it.
In the transition period the DEBUG() macro is still present and aliased
to the LLVM_DEBUG() one.
Differential Revision: https://reviews.llvm.org/D43624
llvm-svn: 332240
We've been running doxygen with the autobrief option for a couple of
years now. This makes the \brief markers into our comments
redundant. Since they are a visual distraction and we don't want to
encourage more \brief markers in new code either, this patch removes
them all.
Patch produced by
for i in $(git grep -l '\\brief'); do perl -pi -e 's/\\brief //g' $i & done
Differential Revision: https://reviews.llvm.org/D46290
llvm-svn: 331272
Summary:
This exposes WebAssembly passes for use on the command line (as
arguments to -print-before and the like).
Reviewers: dschuff, sunfish
Subscribers: MatzeB, jfb, sbc100, llvm-commits, aheejin
Differential Revision: https://reviews.llvm.org/D45103
llvm-svn: 328901
I did this a long time ago with a janky python script, but now
clang-format has built-in support for this. I fed clang-format every
line with a #include and let it re-sort things according to the precise
LLVM rules for include ordering baked into clang-format these days.
I've reverted a number of files where the results of sorting includes
isn't healthy. Either places where we have legacy code relying on
particular include ordering (where possible, I'll fix these separately)
or where we have particular formatting around #include lines that
I didn't want to disturb in this patch.
This patch is *entirely* mechanical. If you get merge conflicts or
anything, just ignore the changes in this patch and run clang-format
over your #include lines in the files.
Sorry for any noise here, but it is important to keep these things
stable. I was seeing an increasing number of patches with irrelevant
re-ordering of #include lines because clang-format was used. This patch
at least isolates that churn, makes it easy to skip when resolving
conflicts, and gets us to a clean baseline (again).
llvm-svn: 304787
Heejin Ahn