These are identified by misc-include-cleaner. I've filtered out those
that break builds. Also, I'm staying away from llvm-config.h,
config.h, and Compiler.h, which likely cause platform- or
compiler-specific build failures.
Currently wasm adds an extra level of options that work backwards
from the standard options, and overwrites them. The ExceptionModel
field in TM->Options is the standard user configuration option for the
exception model to use. MCAsmInfo's ExceptionsType is a constant for the
default to use for the triple if not explicitly set in the TargetOptions
ExceptionModel. This was adding 2 custom flags, changing the MCAsmInfo
default, and overwriting the ExceptionModel from the custom flags.
These comments about compiling bitcode with clang are describing a
toolchain
bug or user error. TargetOptions is bad, and we should move to
eliminating it.
It is module state not captured in the IR. Ideally the exception model
should either
come implied from the triple, or a module flag and not depend on this
side state.
Currently it is the responsibility of the toolchain and/or user to
ensure the same
command line flags are used at each phase of the compilation. It is not
the backend's
responsibilty to try to second guess these options.
-wasm-enable-eh and -wasm-enable-sjlj should also be removed in favor of
the standard
exception control. I'm a bit confused by how all of these fields are
supposed to interact,
but there are a few uses in the backend that are directly looking at
these flags instead
of the already parsed ExceptionModel which need to be cleaned up.
Additionally, this was enforcing some rules about the combinations of
flags at a random
point in the IR pass pipeline configuration. This is a module property
that should
be handled at TargetMachine construction time at the latest. This
required adding flags
to a few mir and clang tests which never got this far to avoid hitting
the errors.
This change is a step towards fixing one long-standing problem with
LLVM's debug WASM codegen: excessive use of locals. One local for each
temporary value in IR (roughly speaking).
This has a lot of problems:
1) It makes it easy to hit engine limitations of 50K locals with certain
code patterns and large functions.
2) It makes for larger binaries that are slower to load and slower to
compile to native code.
3) It makes certain compilation strategies (spill all WASM locals to
stack, for example) for debug code excessively expensive and makes debug
WASM code either run very slow, or be less debuggable.
4) It slows down LLVM itself.
This change addresses these partially by running a limited version of
the stackification pass for unoptimized code, one that gets rid of the
most 'obviously' unnecessary locals.
Care needs to be taken to not impact LLVM's ability to produce high
quality debug variable locations with this pass. To that end:
1) We only allow stackification when it doesn't require moving any
instructions.
2) We disable stackification of any locals that are used in
DEBUG_VALUEs, or as a frame base.
I have verified on a moderately large example that the baseline and the
diff produce the same kinds (local/global/stack) of locations, and the
only differences are due to the shifting of instruction offsets, with
many local.[get|set]s not being present anymore.
Even with this quite conservative approach, the results are pretty good:
1) 30% reduction in raw code size, up to 10x reduction in the number of
locals for select large methods (~1000 => ~100).
2) ~10% reduction in instructions retired for an "llc -O0" run on a
moderately sized input.
## Purpose
This patch is one in a series of code-mods that annotate LLVM’s public
interface for export. This patch annotates the `llvm/Target` library.
These annotations currently have no meaningful impact on the LLVM build;
however, they are a prerequisite to support an LLVM Windows DLL (shared
library) build.
## Background
This effort is tracked in #109483. Additional context is provided in
[this
discourse](https://discourse.llvm.org/t/psa-annotating-llvm-public-interface/85307),
and documentation for `LLVM_ABI` and related annotations is found in the
LLVM repo
[here](https://github.com/llvm/llvm-project/blob/main/llvm/docs/InterfaceExportAnnotations.rst).
A sub-set of these changes were generated automatically using the
[Interface Definition Scanner (IDS)](https://github.com/compnerd/ids)
tool, followed formatting with `git clang-format`.
The bulk of this change is manual additions of `LLVM_ABI` to
`LLVMInitializeX` functions defined in .cpp files under llvm/lib/Target.
Adding `LLVM_ABI` to the function implementation is required here
because they do not `#include "llvm/Support/TargetSelect.h"`, which
contains the declarations for this functions and was already updated
with `LLVM_ABI` in a previous patch. I considered patching these files
with `#include "llvm/Support/TargetSelect.h"` instead, but since
TargetSelect.h is a large file with a bunch of preprocessor x-macro
stuff in it I was concerned it would unnecessarily impact compile times.
In addition, a number of unit tests under llvm/unittests/Target required
additional dependencies to make them build correctly against the LLVM
DLL on Windows using MSVC.
## Validation
Local builds and tests to validate cross-platform compatibility. This
included llvm, clang, and lldb on the following configurations:
- Windows with MSVC
- Windows with Clang
- Linux with GCC
- Linux with Clang
- Darwin with Clang
Register assembly printer passes in the pass registry.
This makes it possible to use `llc -start-before=<target>-asm-printer ...` in tests.
Adds a `char &ID` parameter to the AssemblyPrinter constructor to allow
targets to use the `INITIALIZE_PASS` macros and register the pass in the
pass registry. This currently has a default parameter so it won't break
any targets that have not been updated.
The "using" decl seems to be unused since it was first introduced in:
commit a8e1135baa9074f7c088c8e1999561f88699b56e
Author: Heejin Ahn <aheejin@gmail.com>
Date: Thu Jan 9 22:36:10 2025 -0800
Replace "concept based polymorphism" with simpler PImpl idiom.
This pursues two goals:
* Enforce static type checking. Previously, target implementations hid
base class methods and type checking was impossible. Now that they
override the methods, the compiler will complain on mismatched
signatures.
* Make the code easier to navigate. Previously, if you asked your
favorite LSP server to show a method (e.g. `getInstructionCost()`), it
would show you methods from `TTI`, `TTI::Concept`, `TTI::Model`,
`TTIImplBase`, and target overrides. Now it is two less :)
There are three commits to hopefully simplify the review.
The first commit removes `TTI::Model`. This is done by deriving
`TargetTransformInfoImplBase` from `TTI::Concept`. This is possible
because they implement the same set of interfaces with identical
signatures.
The first commit makes `TargetTransformImplBase` polymorphic, which
means all derived classes should `override` its methods. This is done in
second commit to make the first one smaller. It appeared infeasible to
extract this into a separate PR because the first commit landed
separately would result in tons of `-Woverloaded-virtual` warnings (and
break `-Werror` builds).
The third commit eliminates `TTI::Concept` by merging it with the only
derived class `TargetTransformImplBase`. This commit could be extracted
into a separate PR, but it touches the same lines in
`TargetTransformInfoImpl.h` (removes `override` added by the second
commit and adds `virtual`), so I thought it may make sense to land these
two commits together.
Pull Request: https://github.com/llvm/llvm-project/pull/136674
This replaces the existing `-wasm-enable-exnref` with
`-wasm-use-legacy-eh` option, in an effort to make the new standardized
exnref proposal the 'default' state and the legacy proposal needs to be
separately enabled an option. But given that most users haven't switched
to the new proposal and major web browsers haven't turned it on by
default, this `-wasm-use-legacy-eh` is turned on by default, so nothing
will change for now for the functionality perspective.
This also removes the restriction that `-wasm-enable-exnref` be only
used with `-wasm-enable-eh` because this option is enabled by default.
This option does not have any effect when `-wasm-enable-eh` is not used.
Clang [defaults to aligning `__int128_t` to 16 bytes], while LLVM
`datalayout` strings [default to aligning `i128` to 8 bytes]. Wasm is
currently using the defaults for both, so it's inconsistent. Fix this by
adding `-i128:128` to Wasm's `datalayout` string so that it aligns
`i128` to 16 bytes too.
This is similar to
[llvm/llvm-project@dbad963](dbad963a69)
for SPARC.
This fixesrust-lang/rust#133991; see that issue for further discussion.
[defaults to aligning `__int128_t` to 16 bytes]:
f8b4182f07/clang/lib/Basic/TargetInfo.cpp (L77)
[default to aligning `i128` to 8 bytes]:
https://llvm.org/docs/LangRef.html#langref-datalayout
Following discussions in #110443, and the following earlier discussions
in https://lists.llvm.org/pipermail/llvm-dev/2017-October/117907.html,
https://reviews.llvm.org/D38482, https://reviews.llvm.org/D38489, this
PR attempts to overhaul the `TargetMachine` and `LLVMTargetMachine`
interface classes. More specifically:
1. Makes `TargetMachine` the only class implemented under
`TargetMachine.h` in the `Target` library.
2. `TargetMachine` contains target-specific interface functions that
relate to IR/CodeGen/MC constructs, whereas before (at least on paper)
it was supposed to have only IR/MC constructs. Any Target that doesn't
want to use the independent code generator simply does not implement
them, and returns either `false` or `nullptr`.
3. Renames `LLVMTargetMachine` to `CodeGenCommonTMImpl`. This renaming
aims to make the purpose of `LLVMTargetMachine` clearer. Its interface
was moved under the CodeGen library, to further emphasis its usage in
Targets that use CodeGen directly.
4. Makes `TargetMachine` the only interface used across LLVM and its
projects. With these changes, `CodeGenCommonTMImpl` is simply a set of
shared function implementations of `TargetMachine`, and CodeGen users
don't need to static cast to `LLVMTargetMachine` every time they need a
CodeGen-specific feature of the `TargetMachine`.
5. More importantly, does not change any requirements regarding library
linking.
cc @arsenm @aeubanks
This fixes a problem introduced in #80094. That PR copied negative
features from the TargetMachine to the end of the feature string. This
is not correct, because even if we have a baseline TM of say `-simd128`,
but a function with `+simd128`, the coalesced feature string should have
`+simd128`, not `-simd128`.
To address the original motivation of that PR, we should instead
explicitly materialize the negative features in the target feature
string, so that explicitly disabled default features are honored.
Unfortunately, there doesn't seem to be any way to actually test this
using llc, because `-mattr` appends the specified features to the end of
the `"target-features"` attribute. I've tested this locally by making it
prepend the features instead.
This patch is part of a set of patches that add an `-fextend-lifetimes`
flag to clang, which extends the lifetimes of local variables and
parameters for improved debuggability. In addition to that flag, the
patch series adds a pragma to selectively disable `-fextend-lifetimes`,
and an `-fextend-this-ptr` flag which functions as `-fextend-lifetimes`
for this pointers only. All changes and tests in these patches were
written by Wolfgang Pieb (@wolfy1961), while Stephen Tozer (@SLTozer)
has handled review and merging. The extend lifetimes flag is intended to
eventually be set on by `-Og`, as discussed in the RFC
here:
https://discourse.llvm.org/t/rfc-redefine-og-o1-and-add-a-new-level-of-og/72850
This patch implements a new intrinsic instruction in LLVM,
`llvm.fake.use` in IR and `FAKE_USE` in MIR, that takes a single operand
and has no effect other than "using" its operand, to ensure that its
operand remains live until after the fake use. This patch does not emit
fake uses anywhere; the next patch in this sequence causes them to be
emitted from the clang frontend, such that for each variable (or this) a
fake.use operand is inserted at the end of that variable's scope, using
that variable's value. This patch covers everything post-frontend, which
is largely just the basic plumbing for a new intrinsic/instruction,
along with a few steps to preserve the fake uses through optimizations
(such as moving them ahead of a tail call or translating them through
SROA).
Co-authored-by: Stephen Tozer <stephen.tozer@sony.com>
- Fix build with `EXPENSIVE_CHECKS`
- Remove unused `PassName::ID` to resolve warning
- Mark `~SelectionDAGISel` virtual so AArch64 backend can work properly
This reverts commit de37c06f01772e02465ccc9f538894c76d89a7a1 to
de37c06f01772e02465ccc9f538894c76d89a7a1
It still breaks EXPENSIVE_CHECKS build. Sorry.
Port selection dag isel to new pass manager.
Only `AMDGPU` and `X86` support new pass version. `-verify-machineinstrs` in new pass manager belongs to verify instrumentation, it is enabled by default.
This adds tests for EH/SjLj option errors and swaps the error checking
order for unimportant cosmetic reasons (I think checking EH/SjLj
conflicts is more important than the model checking)
`llvm.trap` will be convert as unreachable which is terminator.
Instruction after terminator will cause validation failed.
This PR introduces a pass to clean instruction after terminator.
Fixes: https://github.com/llvm/llvm-project/issues/68770
Reapply: #90207
`llvm.trap` will be convert as `unreachable` which is terminator.
Instruction after terminator will cause validation failed.
This PR introduces a pass to clean instruction after terminator.
Fixes: #68770.
Currently we check `Subtarget->hasReferenceTypes()` to decide whether to
run `RefTypeMem2Local` pass:
6133878227/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp (L491-L495)
This works fine when `-mattr=+reference-types` is given in the command
line (of `llc` or of `wasm-ld` in case of LTO). This also works fine if
the backend is called by Clang, because Clang's feature set will be
passed to the backend when creating a `TargetMachine`:
ac791888bb/clang/lib/CodeGen/BackendUtil.cpp (L549-L550)ac791888bb/clang/lib/CodeGen/BackendUtil.cpp (L561-L562)
But if the backend compilation is called by `llc`, a `TargetMachine` is
created here:
bf1ad1d267/llvm/tools/llc/llc.cpp (L554-L555)
And if the backend is called by `wasm-ld`'s LTO, a `TargetMachine` is
created here:
ac791888bb/llvm/lib/LTO/LTOBackend.cpp (L513)
At this point, in the both places, the created `TargetMachine` only has
access to target features given by the command line with `-mattr=` and
doesn't have access to bitcode functions' `target-features` attribute.
We later gather the target features used by functions and store that
info in the `TargetMachine` in `CoalesceFeaturesAndStripAtomics`,
ac791888bb/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp (L202-L206)
but this runs in the pass pipeline driven by the pass manager, so this
has not run by the time we check `Subtarget->hasReferenceTypes()` in
`WebAssemblyPassConfig::addISelPrepare`. So currently `RefTypeMem2Local`
would not run on those functions with
`"target-features"="+reference-types"` attributes if the backend is
called by `llc` or `wasm-ld`.
So this makes `RefTypeMem2Local` pass run unconditionally, and checks
`target-featurs` function attribute to decide whether to run the pass on
each function. This allows the pass to run with `wasm-ld` + LTO and
`llc`, even if `-mattr=+reference-types` is not explicitly given in the
command line again, as long as `+reference-types` is in the function's
`target-features` attribute.
This also covers the case we give the target features by the command
line like `llc -mattr=+reference-types` and not in the bitcode
function's attribute, because attributes given in the command line will
be stored in the function's attributes anyway:
bd28889732/llvm/lib/CodeGen/CommandFlags.cpp (L673-L674)bd28889732/llvm/lib/CodeGen/CommandFlags.cpp (L732-L733)
With this PR,
- `lto0.test_externref_emjs`
- `thinlto0.test_externref_emjs`,
- `lto0.test_externref_emjs_dynlink`,
- `thinlto0.test_externref_emjs_dynlnk`
pass. These currently fail but don't get checked in the CI. I think they
used to pass but started to fail after #83196, because we used to run
mem2reg even with `-O0` before that.
(`ltoN` (N > 0) tests are not affected because they run mem2reg anyway
so they don't need `RefTypeMem2Local`)
Multivalue feature of WebAssembly has been standardized for several
years now. I think it makes sense to be able to enable it in the feature
section by default for our clang/llvm-produced binaries so that the
multivalue feature can be used as necessary when necessary within our
toolchain and also when running other optimizers (e.g. wasm-opt) after
the LLVM code generation.
But some WebAssembly toolchains, such as Emscripten, do not provide both
mulvalue-returning and not-multivalue-returning versions of libraries.
Also allowing the uses of multivalue in the features section does not
necessarily mean we generate them whenever we can to the fullest, which
is a different code generation / optimization option.
So this makes the lowering of multivalue returns conditional on the use
of 'experimental-mv' target ABI. This ABI is turned off by default and
turned on by passing `-Xclang -target-abi -Xclang experimental-mv` to
`clang`, or `-target-abi experimental-mv` to `clang -cc1` or `llc`.
But the purpose of this PR is not tying the multivalue lowering to this
specific 'experimental-mv'. 'experimental-mv' is just one multivalue ABI
we currently have, and it is still experimental, meaning it is not very
well optimized or tuned for performance. (e.g. it does not have the
limitation of the max number of multivalue-lowered values, which can be
detrimental to performance.) We may change the name of this ABI, or
improve it, or add a new multivalue ABI in the future. Also I heard that
WASI is planning to add their multivalue ABI soon. So the plan is,
whenever any one of multivalue ABIs is enabled, we enable the lowering
of multivalue returns in the backend. We currently have only
'experimental-mv' in the repo so we only check for that in this PR.
Related past discussions:
#82714https://github.com/WebAssembly/tool-conventions/pull/223#issuecomment-2008298652
Remove `llvm.threadlocal.address` intrinsic usage when disabling TLS.
This fixes errors revealed by the stricter IR verification introduced in
PR #87841.
When reference-types feature is enabled, forcing mem2reg unconditionally
even in `-O0` has some problems described in #81575. This uses
RefTypeMem2Local pass added in #81965 instead. This also removes
`IsForced` parameter added in
890146b192
given that we don't need it anymore.
This may still hurt debug info related to reference type variables a
little during the backend transformation given that they are not stored
in memory anymore, but reference type variables are presumably rare and
it would be still a lot less damage than forcing mem2reg on the whole
program. Also this fixes the EH problem described in #81575.
Fixes#81575.
This reverts commit 6e6bf9f81756ba6655b4eea8dc45469a47f89b39.
It turned out the multivalue feature had active outside users and it
could cause some disruptions to them, so I'd like to investigate more
about the workarounds before doing this.
This adds `WebAssemblyRefTypeMem2Local` pass, which changes the address
spaces of reference type `alloca`s to `addrspace(1)`. This in turn
changes the address spaces of all `load` and `store` instructions that
use the `alloca`s.
`addrspace(1)` is `WASM_ADDRESS_SPACE_VAR`, and loads and stores to this
address space become `local.get`s and `local.set`s, thanks to the Wasm
local IR support added in
82f92e35c6.
In a follow-up PR, I am planning to replace the usage of mem2reg pass
with this to solve the reference type `alloca` problems described in
#81575.
We plan to enable multivalue in the features section soon (#80923) for
other reasons, such as the feature having been standardized for many
years and other features being developed (e.g. EH) depending on it. This
is separate from enabling Clang experimental multivalue ABI (`-Xclang
-target-abi -Xclang experimental-mv`), but it turned out we generate
some multivalue code in the backend as well if it is enabled in the
features section.
Given that our backend multivalue generation still has not been much
used nor tested, and enabling the feature in the features section can be
a separate decision from how much multialue (including none) we decide
to generate for now, I'd like to temporarily disable the actual
generation of multivalue in our backend. To do that, this adds an
internal flag `-wasm-emit-multivalue` that defaults to false. All our
existing multivalue tests can use this to test multivalue code. This
flag can be removed later when we are confident the multivalue
generation is well tested.
In `CoalesceFeaturesAndStripAtomics`, feature string is converted to FeatureBitset and back to feature string. It will lose information about explicit diasbled features.
Currently for any wasm target, llvm will make a pass that removes
irreducible control flow. (See
[here](https://llvm.org/doxygen/WebAssemblyFixIrreducibleControlFlow_8cpp.html)).
This can result in O(NumBlocks * NumNestedLoops * NumIrreducibleLoops +
NumLoops * NumLoops) build time, which has resulted in exceedingly long
build times when testing. This PR introduces a hidden flag to skip this
pass, which brings some of our build times down from 30 minutes to ~6
seconds.
In the WebAssembly back end, the TrapUnreachable option is currently
load-bearing for correctness, inserting wasm `unreachable` instructions
where needed to create valid wasm. There is another option,
NoTrapAfterNoreturn, that removes some of those traps and causes
incorrect wasm to be emitted.
This turns off `NoTrapAfterNoreturn` for the Wasm backend and adds new
tests.
This will make it easy for callers to see issues with and fix up calls
to createTargetMachine after a future change to the params of
TargetMachine.
This matches other nearby enums.
For downstream users, this should be a fairly straightforward
replacement,
e.g. s/CodeGenOpt::Aggressive/CodeGenOptLevel::Aggressive
or s/CGFT_/CodeGenFileType::
Move WebAssemblyUtilities from Utils to the CodeGen library. It
primarily deals in MIR layer types, so it really lives in the CodeGen
library.
Move a variety of other things around to try create better separation.
See issue #64166 for more info on layering.
Move llvm/include/CodeGen/WasmAddressSpaces.h back to
llvm/lib/Target/WebAssembly/Utils.
Differential Revision: https://reviews.llvm.org/D156472
This patch introduces a new type __externref_t that denotes a WebAssembly opaque
reference type. It also implements builtin __builtin_wasm_ref_null_extern(),
that returns a null value of __externref_t. This lays the ground work
for further builtins and reference types.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D122215
This patch introduces a new type __externref_t that denotes a WebAssembly opaque
reference type. It also implements builtin __builtin_wasm_ref_null_extern(),
that returns a null value of __externref_t. This lays the ground work
for further builtins and reference types.
Differential Revision: https://reviews.llvm.org/D122215
Currently default simd alignment is specified by Clang specific TargetInfo
class. This class cannot be reused for LLVM Flang. If we move the default
alignment field into TargetMachine class then we can create TargetMachine
objects and query them to find SIMD alignment.
Scope of changes:
1) Added information about maximal allowed SIMD alignment to TargetMachine
classes.
2) Removed getSimdDefaultAlign function from Clang TargetInfo class.
3) Refactored createTargetMachine function.
Reviewed By: jsjodin
Differential Revision: https://reviews.llvm.org/D138496
This adds the missing handling for defs for target index operands, as is
already done for registers.
There are two kinds of target indices: local indices and stack operands.
- Locals are something similar to registers in Wasm-land. For local
indices, we can check for local-defining instructions (`local.set` or
`local.tee`).
- Wasm is a stack machine, so we have values in certain Wasm value stack
location, which change when Wasm instructions produce or consume
values. So basically any value-producing instrucion, i.e., instruction
with defs, can change values in the Wasm stack. But I think we don't
need to worry about this here, because `WebAssemblyDebugFixup`, which
runs right before this analysis, makes sure to insert terminating
`DBG_VALUE $noreg` instructions whenever a stack value gets popped.
After `WebAssemblyDebugFixup`, there shouldn't be any `DBG_VALUE`s for
stack operands that don't have a terminating `DBG_VALUE $noreg` within
the same BB.
So this CL only works on `DBG_VALUE`s for locals. When we encounter a
`local.set` or `local.tee` instructions, we delete `DBG_VALUE`s for
those target index locations from the open range set, so they will not
be availble in `OutLocs`. For example,
```
bb.0:
successors: %bb.1
DBG_VALUE target-index(wasm-local) + 2, $noreg, "var", ...
...
local.set 2 ...
bb.1:
; predecessors: %bb.0
; We shouldn't add `DBG_VALUE target (wasm-local) + 2 here because
; it was killed by 'local.set' in bb.0
```
After disabling register coalescing at -O1, the average PC ranges
covered for Emscripten core benchmarks is currently 20.6% in the LLVM
tot. After applying D138943 and this CL, the coverage goes up to 57%.
This also enables LiveDebugValues analysis in the Wasm pipeline by
default.
Reviewed By: dschuff, jmorse
Differential Revision: https://reviews.llvm.org/D140373
Follow up to the series:
1. https://reviews.llvm.org/D140161
2. https://reviews.llvm.org/D140349
3. https://reviews.llvm.org/D140331
4. https://reviews.llvm.org/D140323
Completes the work from the previous two for remaining targets.
This creates the following named passes that can be run via
`llc -{start|stop}-{before|after}`:
- arc-isel
- arm-isel
- avr-isel
- bpf-isel
- csky-isel
- hexagon-isel
- lanai-isel
- loongarch-isel
- m68k-isel
- msp430-isel
- mips-isel
- nvptx-isel
- ppc-codegen
- riscv-isel
- sparc-isel
- systemz-isel
- ve-isel
- wasm-isel
- xcore-isel
A nice way to write tests for SelectionDAGISel might be to use a RUN:
line like:
llc -mtriple=<triple> -start-before=<arch>-isel -stop-after=finalize-isel -o -
Fixes: https://github.com/llvm/llvm-project/issues/59538
Reviewed By: asb, zixuan-wu
Differential Revision: https://reviews.llvm.org/D140364
This fixes what I consider to be an API flaw I've tripped over
multiple times. The point this is constructed isn't well defined, so
depending on where this is first called, you can conclude different
information based on the MachineFunction. For example, the AMDGPU
implementation inspected the MachineFrameInfo on construction for the
stack objects and if the frame has calls. This kind of worked in
SelectionDAG which visited all allocas up front, but broke in
GlobalISel which hasn't visited any of the IR when arguments are
lowered.
I've run into similar problems before with the MIR parser and trying
to make use of other MachineFunction fields, so I think it's best to
just categorically disallow dependency on the MachineFunction state in
the constructor and to always construct this at the same time as the
MachineFunction itself.
A missing feature I still could use is a way to access an custom
analysis pass on the IR here.
