* Disable 128-bit atomics for x86_64 generic (currently also baseline)
because they require heavy abi agreement to correctly lower.
** This is a breaking change **
* Enable 128-bit atomics for aarch64 in Sema since it just works.
Since the Zig language documentation claims support for `.Min` and
`.Max` in `@atomicRmw` with floats, allow in Sema and implement for both
the llvm and C backends.
Uses the new liveness behaviour. This also removes useless calls
to `processDeath` on branches that were just initialized. Branch
consolidation and processing deaths on branches inside `condbr`
is still a TODO, just like before.
This also skips var_args on other native backends as they do not
support this feature yet.
Backends want to avoid emitting unused instructions which do not have
side effects: to that end, they all have `Liveness.isUnused` checks for
many instructions. However, checking this in the backends avoids a lot
of potential optimizations. For instance, if a nested field is loaded,
then the first field access would still be emitted, since its result is
used by the next access (which is then unreferenced).
To elide more instructions, Liveness can track this data instead. For
operands which do not have to be lowered (i.e. are not side effecting
and are not something special like `arg), Liveness can ignore their
operand usages, and push the unused information further up, potentially
marking many more instructions as unreferenced.
In doing this, I also uncovered a bug in the LLVM backend relating to
discarding the result of `@cVaArg`, which this change fixes. A behaviour
test has been added to cover it.
Also remove an incorrect piece of logic which allowed fetching the 'len'
property on non-single-ptrs (e.g. many-ptrs) and add a corresponding
compile error test case.
Resolves: #4765
The CI now runs C backend tests in addition to compiling them. It uses
-std=c99 -pedantic -Werror in order to catch non-conformant C code.
This necessitated disabling a test case that caused a C compile error,
in addition to disabling a handful of warnings that are already being
triggered by Zig's C backend output for the behavior tests.
The upshot is that I was able to, very cleanly, integrate the C backend
tests into the build system, so that it communicates via the test runner
protocol along with all the other behavior tests.
This lets us generate the store with knowledge of the type to be stored.
Therefore, we can avoid generating garbage Air with stores through
pointers to comptime-only types which backends cannot lower.
Closes#13410Closes#15122
