NullPropagationTransform rewrote `c != null ? c.AccessChain : default` to
`c?.AccessChain ?? default` whenever the access-chain result was a non-nullable
value type. For a by-ref-like type (a ref struct such as Span<T>) that form does
not compile: a ref struct cannot be wrapped in Nullable<T> (CS8978). Exclude
by-ref-like return types from the null-coalescing rewrite.
Assisted-by: Copilot:claude-opus-4.8:GitHub Copilot CLI
A stackalloc whose result is a pointer is only valid C# as the initializer of a
pointer-typed local. The inliner moved a single-use pointer stackalloc into its
use, producing e.g. 'K.V(stackalloc int[3] { 1, 2, v })' or '*stackalloc ...';
in an expression position the stackalloc is typed as Span<T>, which does not
convert to a pointer, so the output did not compile. Keep such a stackalloc as a
separate local. Moving it into a local store (its declaration) and into the
Span<T>/ReadOnlySpan<T> constructor stay allowed, since those are the positions
where the pointer or span form is exactly what is wanted.
Found while exploring stackalloc-initializer coverage.
Assisted-by: Claude:claude-opus-4-8:Claude Code
HandleSequentialLocAllocInitializer formed a stackalloc initializer whenever the
explicit stores were contiguous from offset 0, even if they did not cover the
whole buffer. A 'stackalloc byte[16]' reinterpreted as int and written through
three of its four elements decompiled to 'stackalloc int[4] { 1, v, 3 }', whose
initializer has fewer elements than the declared length and does not compile.
Require every element to be written (from the constant data blob or an explicit
store) before forming the initializer; otherwise the buffer stays a plain
stackalloc with individual stores.
Found while exploring stackalloc-initializer coverage.
Assisted-by: Claude:claude-opus-4-8:Claude Code
A constant-size stackalloc initializer stores its constant elements through a
data blob (cpblk from a <PrivateImplementationDetails> field). ReadElement
decoded every element by width, so a 4-byte float was read as Int32 and an
8-byte double as Int64. The resulting constant carried the raw bit pattern
(1f decoded as 1.0653532E+09f) and its stack type no longer matched the store,
tripping StObj.CheckInvariant. Dispatch on the element's type code so Single and
Double are read as floating-point, matching the heap-array decoder.
Found while exploring stackalloc-initializer coverage around the element-type
hint fix; floating-point element types had no test case.
Assisted-by: Claude:claude-opus-4-8:Claude Code
Runtime async is a compiler feature that emits ordinary async/await (a
C# 5 construct), so reconstructing it should not require selecting C# 15.
The dedicated RuntimeAsync setting was also redundant: AsyncAwaitDecompiler
already runs the runtime-async transforms only when AsyncAwait is enabled.
Fold the behavior into the AsyncAwait setting and drop the separate toggle.
Assisted-by: Claude:claude-opus-4-8:Claude Code
Convert `call System.Runtime.CompilerServices.AsyncHelpers.Await(value)`
to the IL Await instruction whenever DecompilerSettings.RuntimeAsync is
enabled. The state-machine async pipeline (AsyncAwaitDecompiler) already
produces the IL Await for downstream transforms (UsingTransform's
MatchDisposeBlock pattern-matches on it via UnwrapAwait); doing the
conversion in EarlyExpressionTransforms gives the runtime-async output
the same canonical shape before any consumer runs.
CopyPropagation will replace `ref StructWithStringField reference = ref array[0];` with:
```
var x = array;
var y = 0;
```
and then every use of `reference` is replaced with `x[y]`.
This lets us avoid rough locals while preserving the semantics in every case except that we re-order when a NullReferenceException/IndexOutOfRangeException occurs.
This way we avoid having to extract later, as we will never inline if the `isinst` argument if this could result in it being unrepresentable in C#.
This commit also refactors inlining restrictions to avoid requiring special cases in ILInlining itself.
But when making this change, I discovered that this broke our pattern-matching tests, and that the weird IL with double `isinst` is indeed generated by the C# compiler for `if (genericParam is StringComparison.Ordinal)` style code. So instead we also allow `isinst` with a `box(expr-without-side-effects)` argument to be represented with the `expr is T ? (T)expr : null` emulation.
Sebastien Lebreton
Siegfried Pammer
Nikita
ds5678
Peter Crabtree
Daniel Grunwald