[compiler] Foundation of new mutability and aliasing (alternate take)

Alternate take at a new mutability and alising model, aiming to replace `InferReferenceEffects` and `InferMutableRanges`. My initial passes at this were more complicated than necessary, and I've iterated to refine and distill this down to the core concepts. There are two effects that track information flow: `capture` and `alias`:

* Given distinct values A and B. After capture A -> B, mutate(B) does *not* modify A. This more precisely captures the semantic of the previous `Store` effect. As an example, `array.push(item)` has the effect `capture item -> array` and `mutate(array)`. The array is modified, not the item.
* Given distinct values A and B. After alias A -> B, mutate(B) *does* modify A. This is because B now refers to the same value as A.
* Given distinct values A and B, after *either* capture A -> B *or* alias A -> B, transitiveMutate(B) counts as a mutation of A.

Conceptually "capture A -> B" means that a reference to A was "captured" (or stored) within A, but there is not a directly aliasing. Whereas "alias A -> B" means literal value aliasing.

The idea is that our previous sequential fixpoint loops in InferMutableRanges can instead work by first looking at transitive mutations, then look at non-transitive mutations. And aliasing groups can be built purely based on the `alias` effect.

Lots more to do here but the structure is coming together.

[ghstack-poisoned]
This commit is contained in:
Joe Savona
2025-05-22 16:57:29 -07:00
parent f5cd556ffa
commit 80ae4e96ae
4 changed files with 1225 additions and 17 deletions
@@ -6,6 +6,7 @@
*/
import {CompilerError} from '../CompilerError';
import {AliasingSignature} from '../Inference/InferMutationAliasingEffects';
import {Effect, ValueKind, ValueReason} from './HIR';
import {
BuiltInType,
@@ -179,6 +180,8 @@ export type FunctionSignature = {
impure?: boolean;
canonicalName?: string;
aliasing?: AliasingSignature | null;
};
/*
@@ -332,6 +335,7 @@ addObject(BUILTIN_SHAPES, BuiltInArrayId, [
returnValueKind: ValueKind.Mutable,
noAlias: true,
mutableOnlyIfOperandsAreMutable: true,
aliasing: null,
}),
],
[
@@ -48,7 +48,7 @@ import {
eachTerminalOperand,
eachTerminalSuccessor,
} from '../HIR/visitors';
import {assertExhaustive, retainWhere} from '../Utils/utils';
import {assertExhaustive, retainWhere, Set_isSuperset} from '../Utils/utils';
import {
inferTerminalFunctionEffects,
inferInstructionFunctionEffects,
@@ -790,7 +790,7 @@ function inferParam(
* │ Mutable │───┘
* └──────────────────────────┘
*/
function mergeValues(a: ValueKind, b: ValueKind): ValueKind {
export function mergeValueKinds(a: ValueKind, b: ValueKind): ValueKind {
if (a === b) {
return a;
} else if (a === ValueKind.MaybeFrozen || b === ValueKind.MaybeFrozen) {
@@ -832,28 +832,16 @@ function mergeValues(a: ValueKind, b: ValueKind): ValueKind {
}
}
/**
* @returns `true` if `a` is a superset of `b`.
*/
function isSuperset<T>(a: ReadonlySet<T>, b: ReadonlySet<T>): boolean {
for (const v of b) {
if (!a.has(v)) {
return false;
}
}
return true;
}
function mergeAbstractValues(
a: AbstractValue,
b: AbstractValue,
): AbstractValue {
const kind = mergeValues(a.kind, b.kind);
const kind = mergeValueKinds(a.kind, b.kind);
if (
kind === a.kind &&
kind === b.kind &&
isSuperset(a.reason, b.reason) &&
isSuperset(a.context, b.context)
Set_isSuperset(a.reason, b.reason) &&
Set_isSuperset(a.context, b.context)
) {
return a;
}
@@ -121,6 +121,21 @@ export function Set_intersect<T>(sets: Array<ReadonlySet<T>>): Set<T> {
return result;
}
/**
* @returns `true` if `a` is a superset of `b`.
*/
export function Set_isSuperset<T>(
a: ReadonlySet<T>,
b: ReadonlySet<T>,
): boolean {
for (const v of b) {
if (!a.has(v)) {
return false;
}
}
return true;
}
export function Iterable_some<T>(
iter: Iterable<T>,
pred: (item: T) => boolean,