[NFC] Simplify Array2Struct type replacement#7539
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The logic for joining nullability into a PossibleContents cone value did not previously preserve the exactness of the type in the cone value, causing assertion failures.
Exact references are known to point to exactly their heap type and not one of its subtypes. GUFA already analyzed exactness via the more general "cone" types that include an allowed subtyping depth. Exact types are equivalent to cone types of depth zero. Let GUFA take advantage of exactness information by normalizing cone depths to 0 whenever the cone type is exact.
Array2Struct has to update the types of every expression that interacts with and produces a reference to the optimized array type. It previously did this by separately checking whether a nullable or non-nullable reference to the array was a subtype of the expression's type. Simplify this logic by doing only a single check that considers only the heap types of the references. Also remove some unnecessary variables in which various reference types were cached since it is extremely cheap to materialize a reference type now. These simplifications will also make it easier to update the pass to handle exact reference types once `array.new` instructions are typed as exact.
kripken
approved these changes
Apr 22, 2025
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Array2Struct has to update the types of every expression that interacts
with and produces a reference to the optimized array type. It previously
did this by separately checking whether a nullable or non-nullable
reference to the array was a subtype of the expression's type. Simplify
this logic by doing only a single check that considers only the heap
types of the references.
Also remove some unnecessary variables in which various reference types
were cached since it is extremely cheap to materialize a reference type
now.
These simplifications will also make it easier to update the pass to
handle exact reference types once
array.newinstructions are typed asexact.