See: https://devblogs.microsoft.com/directx/directx-adopting-spir-v
Since we never hooked up the (experimental) DirectX LLVM backend, we've never
actually supported targeting DXIL in Zig. With Microsoft moving away from DXIL,
that seems very unlikely to change.
This commit introduces a new AIR instruction, `repeat`, which causes
control flow to move back to the start of a given AIR loop. `loop`
instructions will no longer automatically perform this operation after
control flow reaches the end of the body.
The motivation for making this change now was really just consistency
with the upcoming implementation of #8220: it wouldn't make sense to
have this feature work significantly differently. However, there were
already some TODOs kicking around which wanted this feature. It's useful
for two key reasons:
* It allows loops over AIR instruction bodies to loop precisely until
they reach a `noreturn` instruction. This allows for tail calling a
few things, and avoiding a range check on each iteration of a hot
path, plus gives a nice assertion that validates AIR structure a
little. This is a very minor benefit, which this commit does apply to
the LLVM and C backends.
* It should allow for more compact ZIR and AIR to be emitted by having
AstGen emit `repeat` instructions more often rather than having
`continue` statements `break` to a `block` which is *followed* by a
`repeat`. This is done in status quo because `repeat` instructions
only ever cause the direct parent block to repeat. Now that AIR is
more flexible, this flexibility can be pretty trivially extended to
ZIR, and we can then emit better ZIR. This commit does not implement
this.
Support for this feature is currently regressed on all self-hosted
native backends, including x86_64. This support will be added where
necessary before this branch is merged.
This commit modifies the representation of the AIR `switch_br`
instruction to represent ranges in cases. Previously, Sema emitted
different AIR in the case of a range, where the `else` branch of the
`switch_br` contained a simple `cond_br` for each such case which did a
simple range check (`x > a and x < b`). Not only does this add
complexity to Sema, which we would like to minimize, but it also gets in
the way of the implementation of #8220. That proposal turns certain
`switch` statements into a looping construct, and for optimization
purposes, we want to lower this to AIR fairly directly (i.e. without
involving a `loop` instruction). That means we would ideally like a
single instruction to represent the entire `switch` statement, so that
we can dispatch back to it with a different operand as in #8220. This is
not really possible to do correctly under the status quo system.
This commit implements lowering of this new `switch_br` usage in the
LLVM and C backends. The C backend just turns any case containing ranges
entirely into conditionals, as before. The LLVM backend is a little
smarter, and puts scalar items into the `switch` instruction, only using
conditionals for the range cases (which direct to the same bb). All
remaining self-hosted backends are temporarily regressed in the presence
of switch range cases. This functionality will be restored for at least
the x86_64 backend before merge.
Passing it by value means that bringup on new architectures is harder for no
real benefit. Passing it by pointer allows to get the compiler running without
needing to figure out the C calling convention details first. This manifested in
practice on LoongArch, for example.
because it marks the linker section, preventing garbage collection.
Also, name the members because that is required by this intrinsic.
Also, enable the StackDepth option in the sancov pass as a workaround
for https://github.com/llvm/llvm-project/pull/106464, otherwise, LLVM
enables TracePCGuard even though we explicitly disable it.
This matches what LLVM's sancov pass does and is required so that
optimization passes do not delete the instrumentation.
However, this is currently triggering an error: "members of
llvm.compiler.used must be named" so the next commit will add names to
those globals.
It's useful to have TraceCmp based on the results of LLVM optimizations,
while the code coverage bits were emitted by Zig manually, allowing more
careful correlation to points of interest in the source code.
This re-enables the sancov pass in `-ffuzz` mode, but only TraceCmp.
Notably, IndirectCalls is off, which needs to be implemented manually in
the LLVM backend, and StackDepth remains off, because it is not used by
libfuzzer or AFL either.
If stack depth is re-introduced, it can be done with better performance
characteristics by being function call graph aware, and only lowered in
call graph cycles, where its heuristic properties come in useful.
Fixes the fuzzing regression.
instead of relying on the LLVM sancov pass. The LLVM pass is still
executed if trace_pc_guard is requested, disabled otherwise. The LLVM
backend emits the instrumentation directly.
It uses `__sancov_pcs1` symbol name instead of `__sancov_pcs` because
each element is 1 usize instead of 2.
AIR: add CoveragePoint to branch hints which indicates whether those
branches are interesting for code coverage purposes.
Update libfuzzer to use the new instrumentation. It's simplified since
we no longer need the constructor and the pcs are now in a continguous
list.
This is a regression in the fuzzing functionality because the
instrumentation for comparisons is no longer emitted, resulting in worse
fuzzer inputs generated. A future commit will add that instrumentation
back.
The compiler actually doesn't need any functional changes for this: Sema
does reification based on the tag indices of `std.builtin.Type` already!
So, no zig1.wasm update is necessary.
This change is necessary to disallow name clashes between fields and
decls on a type, which is a prerequisite of #9938.
Implements the accepted proposal to introduce `@branchHint`. This
builtin is permitted as the first statement of a block if that block is
the direct body of any of the following:
* a function (*not* a `test`)
* either branch of an `if`
* the RHS of a `catch` or `orelse`
* a `switch` prong
* an `or` or `and` expression
It lowers to the ZIR instruction `extended(branch_hint(...))`. When Sema
encounters this instruction, it sets `sema.branch_hint` appropriately,
and `zirCondBr` etc are expected to reset this value as necessary. The
state is on `Sema` rather than `Block` to make it automatically
propagate up non-conditional blocks without special handling. If
`@panic` is reached, the branch hint is set to `.cold` if none was
already set; similarly, error branches get a hint of `.unlikely` if no
hint is explicitly provided. If a condition is comptime-known, `cold`
hints from the taken branch are allowed to propagate up, but other hints
are discarded. This is because a `likely`/`unlikely` hint just indicates
the direction this branch is likely to go, which is redundant
information when the branch is known at comptime; but `cold` hints
indicate that control flow is unlikely to ever reach this branch,
meaning if the branch is always taken from its parent, then the parent
is also unlikely to ever be reached.
This branch information is stored in AIR `cond_br` and `switch_br`. In
addition, `try` and `try_ptr` instructions have variants `try_cold` and
`try_ptr_cold` which indicate that the error case is cold (rather than
just unlikely); this is reachable through e.g. `errdefer unreachable` or
`errdefer @panic("")`.
A new API `unwrapSwitch` is introduced to `Air` to make it more
convenient to access `switch_br` instructions. In time, I plan to update
all AIR instructions to be accessed via an `unwrap` method which returns
a convenient tagged union a la `InternPool.indexToKey`.
The LLVM backend lowers branch hints for conditional branches and
switches as follows:
* If any branch is marked `unpredictable`, the instruction is marked
`!unpredictable`.
* Any branch which is marked as `cold` gets a
`llvm.assume(i1 true) [ "cold"() ]` call to mark the code path cold.
* If any branch is marked `likely` or `unlikely`, branch weight metadata
is attached with `!prof`. Likely branches get a weight of 2000, and
unlikely branches a weight of 1. In `switch` statements, un-annotated
branches get a weight of 1000 as a "middle ground" hint, since there
could be likely *and* unlikely *and* un-annotated branches.
For functions, a `cold` hint corresponds to the `cold` function
attribute, and other hints are currently ignored -- as far as I can tell
LLVM doesn't really have a way to lower them. (Ideally, we would want
the branch hint given in the function to propagate to call sites.)
The compiler and standard library do not yet use this new builtin.
Resolves: #21148
My main gripes with this design were that it was incorrectly namespaced, the naming was inconsistent and a bit wrong (`fooAlign` vs `fooAlignment`).
This commit moves all the logic from `PerThread.zig` to use the zcu + tid system that the previous couple commits introduce.
I've organized and merged the functions to be a bit more specific to their own purpose.
- `fieldAlignment` takes a struct or union type, an index, and a Zcu (or the Sema version which takes a Pt), and gives you the alignment of the field at the index.
- `structFieldAlignment` takes the field type itself, and provides the logic to handle special cases, such as externs.
A design goal I had in mind was to avoid using the word 'struct' in the function name, when it worked for things that aren't structs, such as unions.
This replaces the constant `Zir.Inst.Ref` tags (and the analagous tags
in `Air.Inst.Ref`, `InternPool.Index`) referring to types in
`std.builtin` with a ZIR instruction `extended(builtin_type(...))` which
instructs Sema to fetch such a type, effectively as if it were a
shorthand for the ZIR for `@import("std").builtin.xyz`.
Previously, this was achieved through constant tags in `Ref`. The
analagous `InternPool` indices began as `simple_type` values, and were
later rewritten to the correct type information. This system was kind of
brittle, and more importantly, isn't compatible with incremental
compilation of std, since incremental compilation relies on the ability
to recreate types at different indices when they change. Replacing the
old system with this instruction slightly increases the size of ZIR, but
it simplifies logic and allows incremental compilation to work correctly
on the standard library.
This shouldn't have a significant impact on ZIR size or compiler
performance, but I will take measurements in the PR to confirm this.
This commit makes more progress towards incremental compilation, fixing
some crashes in the frontend. Notably, it fixes the regressions introduced
by #20964. It also cleans up the "outdated file root" mechanism, by
virtue of deleting it: we now detect outdated file roots just after
updating ZIR refs, and re-scan their namespaces.
