Previously, when lowering AIR instructions `wrap_errunion_payload`,
`wrap_errunion_err`, and `wrap_optional`, the LLVM backend would create
an alloca instruction to store the result, but did not set the alignment
on it. This caused UB which went undetected for a long time until we
started enabling the stack protector.
Closes#12594
Unblocks #12508
Inspires #12634
Tests passed locally:
* test-behavior
* test-cases
All tests have been manually verified which are now passing. This means that any remaining
TODO is an actual to-be-fixed or to-be-implemented test case.
* Sema: resolve type fully when emitting an alloc AIR instruction to
avoid tripping assertion for checking struct field alignment.
* LLVM backend: keep a reference to the LLVM target data alive during
lowering so that we can ask LLVM what it thinks the ABI alignment
and size of LLVM types are. We need this in order to lower tuples and
structs so that we can put in extra padding bytes when Zig disagrees
with LLVM about the size or alignment of something.
* LLVM backend: make the LLVM struct type packed that contains the most
aligned union field and the padding. This prevents the struct from
being too big according to LLVM. In the future, we may want to
consider instead emitting unions in a "flat" manner; putting the tag,
most aligned union field, and padding all in the same struct field
space.
* LLVM backend: make structs with 2 or fewer fields return isByRef=false.
This results in more efficient codegen. This required lowering of
bitcast to sometimes store the struct into an alloca, ptrcast, and
then load because LLVM does not allow bitcasting structs.
* enable more passing behavior tests.
The mechanism behind initializing a union's tag is a bit complicated,
depending on whether the union is initialized at runtime,
forced comptime, or implicit comptime.
`coerce_result_ptr` now does not force a block to be a runtime context;
instead of adding runtime instructions directly, it forwards analysis to
the respective functions for initializing optionals and error unions.
`validateUnionInit` now has logic to still emit a runtime
`set_union_tag` instruction even if the union pointer is comptime-known,
for the case of a pointer that is not comptime mutable, such as a
variable or the result of `@intToPtr`.
`validateStructInit` looks for a completely different pattern now; it
now handles the possibility of the corresponding AIR instruction for
the `field_ptr` to be missing or the corresponding `store` to be missing.
See the new comment added to the function for more details. An
equivalent change should probably be made to `validateArrayInit`.
`analyzeOptionalPayloadPtr` and `analyzeErrUnionPayloadPtr` functions now
emit a `optional_payload_ptr_set` or `errunion_payload_ptr_set`
instruction respectively if `initializing` is true and the pointer value
is not comptime-mutable.
`storePtr2` now tries the comptime pointer store before checking if the
element type has one possible value because the comptime pointer store
can have side effects of setting a union tag, setting an optional payload
non-null, or setting an error union to be non-error.
The LLVM backend `lowerParentPtr` function is improved to take into
account the differences in how the LLVM values are lowered depending on
the Zig type. It now handles unions correctly as well as additionally
handling optionals and error unions.
In the LLVM backend, the instructions `optional_payload_ptr_set` and
`errunion_payload_ptr_set` check liveness analysis and only do the side
effects in the case the result of the instruction is unused.
A few wasm and C backend test cases regressed, but they are due to TODOs
in lowering of constants, so this is progress.
Previously, when a coercion needed to be inserted into a break
instruction, the `br` AIR instruction would be rewritten so that the
block operand was a sub-block that did the coercion. The problem is that
the sub-block itself was never added to the parent block, resulting in
the `br` instruction operand being a bad reference.
Now, the `br` AIR instruction that needs to have coercion instructions
added is replaced with the sub-block itself with type `noreturn`, and
then the sub-block has the coercion instructions and a new `br`
instruction that breaks from the original block.
LLVM backend needed to be fixed to lower `noreturn` blocks without
emitting an unused LLVM basic block.
New AIR instruction: `optional_payload_ptr_set`
It's like `optional_payload_ptr` except it sets the non-null bit.
When storing to the payload via a result location that is an optional,
`optional_payload_ptr_set` is now emitted. There is a new algorithm in
`zirCoerceResultPtr` which stores a dummy value through the result
pointer into a temporary block, and then pops off the AIR instructions
from the temporary block in order to determine how to transform the
result location pointer in case any in-between coercions need to happen.
Fixes a couple of behavior tests regarding optionals.
* Sema: implement peer type resolution for optionals and null.
* Rename `Module.optionalType` to `Type.optional`.
* LLVM backend: re-use anonymous values. This is especially useful when
isByRef()=true because it means re-using the same generated LLVM globals.
* LLVM backend: rework the implementation of is_null and is_non_null
AIR instructions. Generate slightly better LLVM code, and also fix
the behavior for optionals whose payload type is 0-bit.
* LLVM backend: improve `cmp` AIR instruction lowering to support
pointer-like optionals.
* `Value`: implement support for equality-checking optionals.
* LLVM backend: The `alloc` AIR instruction as well as pointer
constants which point to a 0-bit element type now call a common
codepath to produce a `*const llvm.Value` which is a non-zero pointer
with a bogus-but-properly-aligned address.
* LLVM backend: improve the lowering of optional types.
* Type: `hasCodeGenBits()` now returns `true` for pointers even when
it returns `false` for their element types.
Effectively, #6706 is now implemented in stage2 but not stage1.
Conflicts:
* doc/langref.html.in
* lib/std/enums.zig
* lib/std/fmt.zig
* lib/std/hash/auto_hash.zig
* lib/std/math.zig
* lib/std/mem.zig
* lib/std/meta.zig
* test/behavior/alignof.zig
* test/behavior/bitcast.zig
* test/behavior/bugs/1421.zig
* test/behavior/cast.zig
* test/behavior/ptrcast.zig
* test/behavior/type_info.zig
* test/behavior/vector.zig
Master branch added `try` to a bunch of testing function calls, and some
lines also had changed how to refer to the native architecture and other
`@import("builtin")` stuff.
