/**

* A control flow analyzer.

* @module flow

*//***/

import {

Type,

TypeFlags,

TypeKind

} from "./types";

import {

Local,

Function,

Element,

ElementKind,

Global

} from "./program";

import {

NativeType,

ExpressionId,

ExpressionRef,

getExpressionId,

getLocalGetIndex,

isLocalTee,

getLocalSetValue,

getGlobalGetName,

getBinaryOp,

BinaryOp,

getBinaryLeft,

getConstValueI32,

getBinaryRight,

getUnaryOp,

UnaryOp,

getExpressionType,

getConstValueI64Low,

getConstValueF32,

getConstValueF64,

getLoadBytes,

isLoadSigned,

getBlockName,

getBlockChildCount,

getBlockChild,

getIfTrue,

getIfFalse,

getSelectThen,

getSelectElse,

getCallTarget,

getLocalSetIndex,

getIfCondition,

getConstValueI64High,

getUnaryValue,

getCallOperand,

traverse

} from "./module";

import {

CommonFlags

} from "./common";

import {

DiagnosticCode

} from "./diagnostics";

import {

Node

} from "./ast";

/** Control flow flags indicating specific conditions. */

export const enum FlowFlags {

/** No specific conditions. */

NONE = 0,

// categorical

/** This flow returns. */

RETURNS = 1 << 0,

/** This flow returns a wrapped value. */

RETURNS_WRAPPED = 1 << 1,

/** This flow returns a non-null value. */

RETURNS_NONNULL = 1 << 2,

/** This flow throws. */

THROWS = 1 << 3,

/** This flow breaks. */

BREAKS = 1 << 4,

/** This flow continues. */

CONTINUES = 1 << 5,

/** This flow allocates. Constructors only. */

ALLOCATES = 1 << 6,

/** This flow calls super. Constructors only. */

CALLS_SUPER = 1 << 7,

/** This flow terminates (returns, throws or continues). */

TERMINATES = 1 << 8,

// conditional

/** This flow conditionally returns in a child flow. */

CONDITIONALLY_RETURNS = 1 << 9,

/** This flow conditionally throws in a child flow. */

CONDITIONALLY_THROWS = 1 << 10,

/** This flow conditionally terminates in a child flow. */

CONDITIONALLY_TERMINATES = 1 << 11,

/** This flow conditionally breaks in a child flow. */

CONDITIONALLY_BREAKS = 1 << 12,

/** This flow conditionally continues in a child flow. */

CONDITIONALLY_CONTINUES = 1 << 13,

/** This flow conditionally allocates in a child flow. Constructors only. */

CONDITIONALLY_ALLOCATES = 1 << 14,

// special

/** This is an inlining flow. */

INLINE_CONTEXT = 1 << 15,

/** This is a flow with explicitly disabled bounds checking. */

UNCHECKED_CONTEXT = 1 << 16,

// masks

/** Any categorical flag. */

ANY_CATEGORICAL = FlowFlags.RETURNS

| FlowFlags.RETURNS_WRAPPED

| FlowFlags.RETURNS_NONNULL

| FlowFlags.THROWS

| FlowFlags.BREAKS

| FlowFlags.CONTINUES

| FlowFlags.ALLOCATES

| FlowFlags.CALLS_SUPER

| FlowFlags.TERMINATES,

/** Any conditional flag. */

ANY_CONDITIONAL = FlowFlags.CONDITIONALLY_RETURNS

| FlowFlags.CONDITIONALLY_THROWS

| FlowFlags.CONDITIONALLY_BREAKS

| FlowFlags.CONDITIONALLY_CONTINUES

| FlowFlags.CONDITIONALLY_ALLOCATES

}

/** Flags indicating the current state of a local. */

export enum LocalFlags {

/** No specific conditions. */

NONE = 0,

/** Local is constant. */

CONSTANT = 1 << 0,

/** Local is a function parameter. */

PARAMETER = 1 << 1,

/** Local is properly wrapped. Relevant for small integers. */

WRAPPED = 1 << 2,

/** Local is non-null. */

NONNULL = 1 << 3,

/** Local is read from. */

READFROM = 1 << 4,

/** Local is written to. */

WRITTENTO = 1 << 5,

/** Local is retained. */

RETAINED = 1 << 6,

/** Local is returned. */

RETURNED = 1 << 7,

/** Local is conditionally read from. */

CONDITIONALLY_READFROM = 1 << 8,

/** Local is conditionally written to. */

CONDITIONALLY_WRITTENTO = 1 << 9,

/** Local must be conditionally retained. */

CONDITIONALLY_RETAINED = 1 << 10,

/** Local is conditionally returned. */

CONDITIONALLY_RETURNED = 1 << 11,

/** Any categorical flag. */

ANY_CATEGORICAL = CONSTANT

| PARAMETER

| WRAPPED

| NONNULL

| READFROM

| WRITTENTO

| RETAINED

| RETURNED,

/** Any conditional flag. */

ANY_CONDITIONAL = RETAINED

| CONDITIONALLY_READFROM

| CONDITIONALLY_WRITTENTO

| CONDITIONALLY_RETAINED

| CONDITIONALLY_RETURNED,

/** Any written to flag. */

ANY_WRITTENTO = WRITTENTO

| CONDITIONALLY_WRITTENTO,

/** Any retained flag. */

ANY_RETAINED = RETAINED

| CONDITIONALLY_RETAINED,

/** Any returned flag. */

ANY_RETURNED = RETURNED

| CONDITIONALLY_RETURNED

}

export namespace LocalFlags {

export function join(left: LocalFlags, right: LocalFlags): LocalFlags {

return ((left & LocalFlags.ANY_CATEGORICAL) & (right & LocalFlags.ANY_CATEGORICAL))

| (left & LocalFlags.ANY_CONDITIONAL) | (right & LocalFlags.ANY_CONDITIONAL);

}

}

/** Flags indicating the current state of a field. */

export enum FieldFlags {

/** No specific conditions. */

NONE = 0,

/** Field is initialized. Relevant in constructors. */

INITIALIZED = 1 << 0,

/** Field is conditionally initialized. Relevant in constructors. */

CONDITIONALLY_INITIALIZED = 1 << 1,

/** Any categorical flag. */

ANY_CATEGORICAL = INITIALIZED,

/** Any conditional flag. */

ANY_CONDITIONAL = CONDITIONALLY_INITIALIZED

}

export namespace FieldFlags {

export function join(left: FieldFlags, right: FieldFlags): FieldFlags {

return ((left & FieldFlags.ANY_CATEGORICAL) & (right & FieldFlags.ANY_CATEGORICAL))

| (left & FieldFlags.ANY_CONDITIONAL) | (right & FieldFlags.ANY_CONDITIONAL);

}

}

/** A control flow evaluator. */

export class Flow {

/** Parent flow. */

parent: Flow | null;

/** Flow flags indicating specific conditions. */

flags: FlowFlags;

/** Function this flow belongs to. */

parentFunction: Function;

/** The label we break to when encountering a continue statement. */

continueLabel: string | null;

/** The label we break to when encountering a break statement. */

breakLabel: string | null;

/** The current return type. */

returnType: Type;

/** The current contextual type arguments. */

contextualTypeArguments: Map<string,Type> | null;

/** Scoped local variables. */

scopedLocals: Map<string,Local> | null = null;

/** Local flags. */

localFlags: LocalFlags[];

/** Field flags. Relevant in constructors. */

fieldFlags: Map<string,FieldFlags> | null = null;

/** Function being inlined, when inlining. */

inlineFunction: Function | null;

/** The label we break to when encountering a return statement, when inlining. */

inlineReturnLabel: string | null;

/** Creates the parent flow of the specified function. */

static create(parentFunction: Function): Flow {

var flow = new Flow();

flow.parent = null;

flow.flags = FlowFlags.NONE;

flow.parentFunction = parentFunction;

flow.continueLabel = null;

flow.breakLabel = null;

flow.returnType = parentFunction.signature.returnType;

flow.contextualTypeArguments = parentFunction.contextualTypeArguments;

flow.localFlags = [];

flow.inlineFunction = null;

flow.inlineReturnLabel = null;

return flow;

}

/** Creates an inline flow within `parentFunction`. */

static createInline(parentFunction: Function, inlineFunction: Function): Flow {

var flow = Flow.create(parentFunction);

flow.set(FlowFlags.INLINE_CONTEXT);

flow.inlineFunction = inlineFunction;

flow.inlineReturnLabel = inlineFunction.internalName + "|inlined." + (inlineFunction.nextInlineId++).toString(10);

flow.returnType = inlineFunction.signature.returnType;

flow.contextualTypeArguments = inlineFunction.contextualTypeArguments;

return flow;

}

private constructor() { }

/** Gets the actual function being compiled, The inlined function when inlining, otherwise the parent function. */

get actualFunction(): Function {

return this.inlineFunction || this.parentFunction;

}

/** Tests if this flow has the specified flag or flags. */

is(flag: FlowFlags): bool { return (this.flags & flag) == flag; }

/** Tests if this flow has one of the specified flags. */

isAny(flag: FlowFlags): bool { return (this.flags & flag) != 0; }

/** Sets the specified flag or flags. */

set(flag: FlowFlags): void { this.flags |= flag; }

/** Unsets the specified flag or flags. */

unset(flag: FlowFlags): void { this.flags &= ~flag; }

/** Forks this flow to a child flow. */

fork(): Flow {

var branch = new Flow();

branch.parent = this;

branch.flags = this.flags;

branch.parentFunction = this.parentFunction;

branch.continueLabel = this.continueLabel;

branch.breakLabel = this.breakLabel;

branch.returnType = this.returnType;

branch.contextualTypeArguments = this.contextualTypeArguments;

branch.localFlags = this.localFlags.slice();

branch.inlineFunction = this.inlineFunction;

branch.inlineReturnLabel = this.inlineReturnLabel;

return branch;

}

/** Gets a free temporary local of the specified type. */

getTempLocal(type: Type, except: Set<i32> | null = null): Local {

var parentFunction = this.parentFunction;

var temps: Local[] | null;

switch (type.toNativeType()) {

case NativeType.I32: { temps = parentFunction.tempI32s; break; }

case NativeType.I64: { temps = parentFunction.tempI64s; break; }

case NativeType.F32: { temps = parentFunction.tempF32s; break; }

case NativeType.F64: { temps = parentFunction.tempF64s; break; }

case NativeType.V128: { temps = parentFunction.tempV128s; break; }

default: throw new Error("concrete type expected");

}

var local: Local;

if (except) {

if (temps && temps.length) {

for (let i = 0, k = temps.length; i < k; ++i) {

if (!except.has(temps[i].index)) {

local = temps[i];

let k = temps.length - 1;

while (i < k) unchecked(temps[i] = temps[i++ + 1]);

temps.length = k;

local.type = type;

local.flags = CommonFlags.NONE;

this.unsetLocalFlag(local.index, ~0);

return local;

}

}

}

local = parentFunction.addLocal(type);

} else {

if (temps && temps.length) {

local = temps.pop()!;

local.type = type;

local.flags = CommonFlags.NONE;

} else {

local = parentFunction.addLocal(type);

}

}

this.unsetLocalFlag(local.index, ~0);

return local;

}

/** Gets a local that sticks around until this flow is exited, and then released. */

getAutoreleaseLocal(type: Type, except: Set<i32> | null = null): Local {

var local = this.getTempLocal(type, except);

local.set(CommonFlags.SCOPED);

var scopedLocals = this.scopedLocals;

if (!scopedLocals) this.scopedLocals = scopedLocals = new Map();

scopedLocals.set("~auto" + (this.parentFunction.nextAutoreleaseId++), local);

this.setLocalFlag(local.index, LocalFlags.RETAINED);

return local;

}

/** Frees the temporary local for reuse. */

freeTempLocal(local: Local): void {

if (local.is(CommonFlags.INLINED)) return;

assert(local.index >= 0);

var parentFunction = this.parentFunction;

var temps: Local[];

assert(local.type != null); // internal error

switch ((<Type>local.type).toNativeType()) {

case NativeType.I32: {

temps = parentFunction.tempI32s || (parentFunction.tempI32s = []);

break;

}

case NativeType.I64: {

temps = parentFunction.tempI64s || (parentFunction.tempI64s = []);

break;

}

case NativeType.F32: {

temps = parentFunction.tempF32s || (parentFunction.tempF32s = []);

break;

}

case NativeType.F64: {

temps = parentFunction.tempF64s || (parentFunction.tempF64s = []);

break;

}

case NativeType.V128: {

temps = parentFunction.tempV128s || (parentFunction.tempV128s = []);

break;

}

default: throw new Error("concrete type expected");

}

assert(local.index >= 0);

temps.push(local);

}

/** Gets the scoped local of the specified name. */

getScopedLocal(name: string): Local | null {

var scopedLocals = this.scopedLocals;

if (scopedLocals && scopedLocals.has(name)) return scopedLocals.get(name)!;

return null;

}

/** Adds a new scoped local of the specified name. */

addScopedLocal(name: string, type: Type, except: Set<i32> | null = null): Local {

var scopedLocal = this.getTempLocal(type, except);

var scopedLocals = this.scopedLocals;

if (!scopedLocals) this.scopedLocals = scopedLocals = new Map();

else assert(!scopedLocals.has(name));

scopedLocal.set(CommonFlags.SCOPED);

scopedLocals.set(name, scopedLocal);

return scopedLocal;

}

/** Adds a new scoped alias for the specified local. For example `super` aliased to the `this` local. */

addScopedAlias(name: string, type: Type, index: i32, reportNode: Node | null = null): Local {

if (!this.scopedLocals) this.scopedLocals = new Map();

else {

let existingLocal = this.scopedLocals.get(name);

if (existingLocal) {

if (reportNode) {

if (!existingLocal.declaration.range.source.isNative) {

this.parentFunction.program.errorRelated(

DiagnosticCode.Duplicate_identifier_0,

reportNode.range,

existingLocal.declaration.name.range,

name

);

} else {

this.parentFunction.program.error(

DiagnosticCode.Duplicate_identifier_0,

reportNode.range, name

);

}

}

return existingLocal;

}

}

assert(index < this.parentFunction.localsByIndex.length);

var scopedAlias = new Local(name, index, type, this.parentFunction);

// not flagged as SCOPED as it must not be free'd when the flow is finalized

this.scopedLocals.set(name, scopedAlias);

return scopedAlias;

}

/** Tests if this flow has any scoped locals that must be free'd. */

get hasScopedLocals(): bool {

if (this.scopedLocals) {

for (let scopedLocal of this.scopedLocals.values()) {

if (scopedLocal.is(CommonFlags.SCOPED)) { // otherwise an alias

return true;

}

}

}

return false;

}

/** Frees this flow's scoped variables and returns its parent flow. */

freeScopedLocals(): void {

if (this.scopedLocals) {

for (let scopedLocal of this.scopedLocals.values()) {

if (scopedLocal.is(CommonFlags.SCOPED)) { // otherwise an alias

this.freeTempLocal(scopedLocal);

}

}

this.scopedLocals = null;

}

}

/** Looks up the local of the specified name in the current scope. */

lookupLocal(name: string): Local | null {

var current: Flow | null = this;

var scope: Map<String,Local> | null;

do if ((scope = current.scopedLocals) && (scope.has(name))) return scope.get(name)!;

while (current = current.parent);

return this.parentFunction.localsByName.get(name)!;

}

/** Looks up the element with the specified name relative to the scope of this flow. */

lookup(name: string): Element | null {

var element = this.lookupLocal(name);

if (element) return element;

return this.actualFunction.lookup(name);

}

/** Tests if the local at the specified index has the specified flag or flags. */

isLocalFlag(index: i32, flag: LocalFlags, defaultIfInlined: bool = true): bool {

if (index < 0) return defaultIfInlined;

var localFlags = this.localFlags;

return index < localFlags.length && (unchecked(this.localFlags[index]) & flag) == flag;

}

/** Tests if the local at the specified index has any of the specified flags. */

isAnyLocalFlag(index: i32, flag: LocalFlags, defaultIfInlined: bool = true): bool {

if (index < 0) return defaultIfInlined;

var localFlags = this.localFlags;

return index < localFlags.length && (unchecked(this.localFlags[index]) & flag) != 0;

}

/** Sets the specified flag or flags on the local at the specified index. */

setLocalFlag(index: i32, flag: LocalFlags): void {

if (index < 0) return;

var localFlags = this.localFlags;

var flags = index < localFlags.length ? unchecked(localFlags[index]) : 0;

this.localFlags[index] = flags | flag;

}

/** Unsets the specified flag or flags on the local at the specified index. */

unsetLocalFlag(index: i32, flag: LocalFlags): void {

if (index < 0) return;

var localFlags = this.localFlags;

var flags = index < localFlags.length ? unchecked(localFlags[index]) : 0;

this.localFlags[index] = flags & ~flag;

}

/** Pushes a new break label to the stack, for example when entering a loop that one can `break` from. */

pushBreakLabel(): string {

var parentFunction = this.parentFunction;

var id = parentFunction.nextBreakId++;

var stack = parentFunction.breakStack;

if (!stack) parentFunction.breakStack = [ id ];

else stack.push(id);

return parentFunction.breakLabel = id.toString(10);

}

/** Pops the most recent break label from the stack. */

popBreakLabel(): void {

var parentFunction = this.parentFunction;

var stack = assert(parentFunction.breakStack);

var length = assert(stack.length);

stack.pop();

if (length > 1) {

parentFunction.breakLabel = stack[length - 2].toString(10);

} else {

parentFunction.breakLabel = null;

parentFunction.breakStack = null;

}

}

/** Inherits flags and local wrap states from the specified flow (e.g. blocks). */

inherit(other: Flow): void {

this.flags |= other.flags & (FlowFlags.ANY_CATEGORICAL | FlowFlags.ANY_CONDITIONAL);

this.localFlags = other.localFlags; // no need to slice because other flow is finished

}

/** Inherits categorical flags as conditional flags from the specified flow (e.g. then without else). */

inheritConditional(other: Flow): void {

this.set(other.flags & FlowFlags.ANY_CONDITIONAL);

if (other.is(FlowFlags.RETURNS)) {

this.set(FlowFlags.CONDITIONALLY_RETURNS);

}

if (other.is(FlowFlags.THROWS)) {

this.set(FlowFlags.CONDITIONALLY_THROWS);

}

if (other.is(FlowFlags.BREAKS) && other.breakLabel == this.breakLabel) {

this.set(FlowFlags.CONDITIONALLY_BREAKS);

}

if (other.is(FlowFlags.CONTINUES) && other.continueLabel == this.continueLabel) {

this.set(FlowFlags.CONDITIONALLY_CONTINUES);

}

if (other.is(FlowFlags.ALLOCATES)) {

this.set(FlowFlags.CONDITIONALLY_ALLOCATES);

}

var localFlags = other.localFlags;

for (let i = 0, k = localFlags.length; i < k; ++i) {

let flags = localFlags[i];

this.setLocalFlag(i, flags & LocalFlags.ANY_CONDITIONAL);

if (flags & LocalFlags.RETAINED) this.setLocalFlag(i, LocalFlags.CONDITIONALLY_RETAINED);

if (flags & LocalFlags.READFROM) this.setLocalFlag(i, LocalFlags.CONDITIONALLY_READFROM);

if (flags & LocalFlags.WRITTENTO) this.setLocalFlag(i, LocalFlags.CONDITIONALLY_WRITTENTO);

if (flags & LocalFlags.RETURNED) this.setLocalFlag(i, LocalFlags.CONDITIONALLY_RETURNED);

}

}

/** Inherits mutual flags and local wrap states from the specified flows (e.g. then with else). */

inheritMutual(left: Flow, right: Flow): void {

// categorical flags set in both arms

this.set(left.flags & right.flags & FlowFlags.ANY_CATEGORICAL);

// conditional flags set in any arm

this.set(left.flags & FlowFlags.ANY_CONDITIONAL);

this.set(right.flags & FlowFlags.ANY_CONDITIONAL);

// categorical flags in either arm as conditional

this.inheritConditional(left);

this.inheritConditional(right);

// categorical local flags set in both arms / conditional local flags set in at least one arm

var leftLocalFlags = left.localFlags;

var numLeftLocalFlags = leftLocalFlags.length;

var rightLocalFlags = right.localFlags;

var numRightLocalFlags = rightLocalFlags.length;

var combinedFlags = new Array<LocalFlags>(max<i32>(numLeftLocalFlags, numRightLocalFlags));

for (let i = 0; i < numLeftLocalFlags; ++i) {

combinedFlags[i] = LocalFlags.join(

unchecked(leftLocalFlags[i]),

i < numRightLocalFlags

? unchecked(rightLocalFlags[i])

: 0

);

}

for (let i = numLeftLocalFlags; i < numRightLocalFlags; ++i) {

combinedFlags[i] = LocalFlags.join(

0,

unchecked(rightLocalFlags[i])

);

}

this.localFlags = combinedFlags;

}

/** Unifies local flags between this and the other flow. */

unifyLocalFlags(other: Flow): void {

var numThisLocalFlags = this.localFlags.length;

var numOtherLocalFlags = other.localFlags.length;

for (let i = 0, k = min<i32>(numThisLocalFlags, numOtherLocalFlags); i < k; ++i) {

if (this.isLocalFlag(i, LocalFlags.WRAPPED) != other.isLocalFlag(i, LocalFlags.WRAPPED)) {

this.unsetLocalFlag(i, LocalFlags.WRAPPED); // assume not wrapped

}

if (this.isLocalFlag(i, LocalFlags.NONNULL) != other.isLocalFlag(i, LocalFlags.NONNULL)) {

this.unsetLocalFlag(i, LocalFlags.NONNULL); // assume possibly null

}

assert(

// having different retain states would be a problem because the compiler

// either can't release a retained local or would release a non-retained local

this.isAnyLocalFlag(i, LocalFlags.ANY_RETAINED) == other.isAnyLocalFlag(i, LocalFlags.ANY_RETAINED)

);

}

}

/** Checks if an expression of the specified type is known to be non-null, even if the type might be nullable. */

isNonnull(expr: ExpressionRef, type: Type): bool {

if (!type.is(TypeFlags.NULLABLE)) return true;

// below, only teeLocal/getLocal are relevant because these are the only expressions that

// depend on a dynamic nullable state (flag = LocalFlags.NONNULL), while everything else

// has already been handled by the nullable type check above.

switch (getExpressionId(expr)) {

case ExpressionId.LocalSet: {

if (!isLocalTee(expr)) break;

let local = this.parentFunction.localsByIndex[getLocalSetIndex(expr)];

return !local.type.is(TypeFlags.NULLABLE) || this.isLocalFlag(local.index, LocalFlags.NONNULL, false);

}

case ExpressionId.LocalGet: {

let local = this.parentFunction.localsByIndex[getLocalGetIndex(expr)];

return !local.type.is(TypeFlags.NULLABLE) || this.isLocalFlag(local.index, LocalFlags.NONNULL, false);

}

}

return false;

}

/** Updates local states to reflect that this branch is only taken when `expr` is true-ish. */

inheritNonnullIfTrue(expr: ExpressionRef): void {

// A: `expr` is true-ish -> Q: how did that happen?

switch (getExpressionId(expr)) {

case ExpressionId.LocalSet: {

if (!isLocalTee(expr)) break;

let local = this.parentFunction.localsByIndex[getLocalSetIndex(expr)];

this.setLocalFlag(local.index, LocalFlags.NONNULL);

this.inheritNonnullIfTrue(getLocalSetValue(expr)); // must have been true-ish as well

break;

}

case ExpressionId.LocalGet: {

let local = this.parentFunction.localsByIndex[getLocalGetIndex(expr)];

this.setLocalFlag(local.index, LocalFlags.NONNULL);

break;

}

case ExpressionId.If: {

let ifFalse = getIfFalse(expr);

if (!ifFalse) break;

if (getExpressionId(ifFalse) == ExpressionId.Const) {

// Logical AND: (if (condition ifTrue 0))

// the only way this had become true is if condition and ifTrue are true

if (

(getExpressionType(ifFalse) == NativeType.I32 && getConstValueI32(ifFalse) == 0) ||

(getExpressionType(ifFalse) == NativeType.I64 && getConstValueI64Low(ifFalse) == 0 && getConstValueI64High(ifFalse) == 0)

) {

this.inheritNonnullIfTrue(getIfCondition(expr));

this.inheritNonnullIfTrue(getIfTrue(expr));

}

}

break;

}

case ExpressionId.Unary: {

switch (getUnaryOp(expr)) {

case UnaryOp.EqzI32:

case UnaryOp.EqzI64: {

this.inheritNonnullIfFalse(getUnaryValue(expr)); // !value -> value must have been false

break;

}

}

break;

}

case ExpressionId.Binary: {

switch (getBinaryOp(expr)) {

case BinaryOp.EqI32: {

let left = getBinaryLeft(expr);

let right = getBinaryRight(expr);

if (getExpressionId(left) == ExpressionId.Const && getConstValueI32(left) != 0) {

this.inheritNonnullIfTrue(right); // TRUE == right -> right must have been true

} else if (getExpressionId(right) == ExpressionId.Const && getConstValueI32(right) != 0) {

this.inheritNonnullIfTrue(left); // left == TRUE -> left must have been true

}

break;

}

case BinaryOp.EqI64: {

let left = getBinaryLeft(expr);

let right = getBinaryRight(expr);

if (getExpressionId(left) == ExpressionId.Const && (getConstValueI64Low(left) != 0 || getConstValueI64High(left) != 0)) {

this.inheritNonnullIfTrue(right); // TRUE == right -> right must have been true

} else if (getExpressionId(right) == ExpressionId.Const && (getConstValueI64Low(right) != 0 && getConstValueI64High(right) != 0)) {

this.inheritNonnullIfTrue(left); // left == TRUE -> left must have been true

}

break;

}

case BinaryOp.NeI32: {

let left = getBinaryLeft(expr);

let right = getBinaryRight(expr);

if (getExpressionId(left) == ExpressionId.Const && getConstValueI32(left) == 0) {

this.inheritNonnullIfTrue(right); // FALSE != right -> right must have been true

} else if (getExpressionId(right) == ExpressionId.Const && getConstValueI32(right) == 0) {

this.inheritNonnullIfTrue(left); // left != FALSE -> left must have been true

}

break;

}

case BinaryOp.NeI64: {

let left = getBinaryLeft(expr);

let right = getBinaryRight(expr);

if (getExpressionId(left) == ExpressionId.Const && getConstValueI64Low(left) == 0 && getConstValueI64High(left) == 0) {

this.inheritNonnullIfTrue(right); // FALSE != right -> right must have been true

} else if (getExpressionId(right) == ExpressionId.Const && getConstValueI64Low(right) == 0 && getConstValueI64High(right) == 0) {

this.inheritNonnullIfTrue(left); // left != FALSE -> left must have been true

}

break;

}

}

break;

}

case ExpressionId.Call: {

let name = getCallTarget(expr);

let program = this.parentFunction.program;

switch (name) {

case program.retainInstance.internalName: {

this.inheritNonnullIfTrue(getCallOperand(expr, 0));

break;

}

}

break;

}

}

}

/** Updates local states to reflect that this branch is only taken when `expr` is false-ish. */

inheritNonnullIfFalse(expr: ExpressionRef): void {

// A: `expr` is false-ish -> Q: how did that happen?

switch (getExpressionId(expr)) {

case ExpressionId.Unary: {

switch (getUnaryOp(expr)) {

case UnaryOp.EqzI32:

case UnaryOp.EqzI64: {

this.inheritNonnullIfTrue(getUnaryValue(expr)); // !value -> value must have been true

break;

}

}

break;

}

case ExpressionId.If: {

let ifTrue = getIfTrue(expr);

if (getExpressionId(ifTrue) == ExpressionId.Const) {

let ifFalse = getIfFalse(expr);

if (!ifFalse) break;

// Logical OR: (if (condition 1 ifFalse))

// the only way this had become false is if condition and ifFalse are false

if (

(getExpressionType(ifTrue) == NativeType.I32 && getConstValueI32(ifTrue) != 0) ||

(getExpressionType(ifTrue) == NativeType.I64 && (getConstValueI64Low(ifTrue) != 0 || getConstValueI64High(ifTrue) != 0))

) {

this.inheritNonnullIfFalse(getIfCondition(expr));

this.inheritNonnullIfFalse(getIfFalse(expr));

}

}

break;

}

case ExpressionId.Binary: {

switch (getBinaryOp(expr)) {

// remember: we want to know how the _entire_ expression became FALSE (!)

case BinaryOp.EqI32: {

let left = getBinaryLeft(expr);

let right = getBinaryRight(expr);

if (getExpressionId(left) == ExpressionId.Const && getConstValueI32(left) == 0) {

this.inheritNonnullIfTrue(right); // FALSE == right -> right must have been true

} else if (getExpressionId(right) == ExpressionId.Const && getConstValueI32(right) == 0) {

this.inheritNonnullIfTrue(left); // left == FALSE -> left must have been true

}

break;

}

case BinaryOp.EqI64: {

let left = getBinaryLeft(expr);

let right = getBinaryRight(expr);

if (getExpressionId(left) == ExpressionId.Const && getConstValueI64Low(left) == 0 && getConstValueI64High(left) == 0) {

this.inheritNonnullIfTrue(right); // FALSE == right -> right must have been true

} else if (getExpressionId(right) == ExpressionId.Const && getConstValueI64Low(right) == 0 && getConstValueI64High(right) == 0) {

this.inheritNonnullIfTrue(left); // left == FALSE -> left must have been true

}

break;

}

case BinaryOp.NeI32: {

let left = getBinaryLeft(expr);

let right = getBinaryRight(expr);

if (getExpressionId(left) == ExpressionId.Const && getConstValueI32(left) != 0) {

this.inheritNonnullIfTrue(right); // TRUE != right -> right must have been true

} else if (getExpressionId(right) == ExpressionId.Const && getConstValueI32(right) != 0) {

this.inheritNonnullIfTrue(left); // left != TRUE -> left must have been true

}

break;

}

case BinaryOp.NeI64: {

let left = getBinaryLeft(expr);

let right = getBinaryRight(expr);

if (getExpressionId(left) == ExpressionId.Const && (getConstValueI64Low(left) != 0 || getConstValueI64High(left) != 0)) {

this.inheritNonnullIfTrue(right); // TRUE != right -> right must have been true for this to become false

} else if (getExpressionId(right) == ExpressionId.Const && (getConstValueI64Low(right) != 0 || getConstValueI64High(right) != 0)) {

this.inheritNonnullIfTrue(left); // left != TRUE -> left must have been true for this to become false

}

break;

}

}

break;

}

}

}

/**

* Tests if an expression can possibly overflow in the context of this flow. Assumes that the

* expression might already have overflown and returns `false` only if the operation neglects

* any possible combination of garbage bits being present.

*/

canOverflow(expr: ExpressionRef, type: Type): bool {

// TODO: the following catches most common and a few uncommon cases, but there are additional

// opportunities here, obviously.

assert(type != Type.void);

// types other than i8, u8, i16, u16 and bool do not overflow

if (!type.is(TypeFlags.SHORT | TypeFlags.INTEGER)) return false;

var operand: ExpressionRef;

switch (getExpressionId(expr)) {

// overflows if the local isn't wrapped or the conversion does

case ExpressionId.LocalGet: {

let local = this.parentFunction.localsByIndex[getLocalGetIndex(expr)];

return !this.isLocalFlag(local.index, LocalFlags.WRAPPED, true)

|| canConversionOverflow(local.type, type);

}

// overflows if the value does

case ExpressionId.LocalSet: { // tee

assert(isLocalTee(expr));

return this.canOverflow(getLocalSetValue(expr), type);

}

// overflows if the conversion does (globals are wrapped on set)

case ExpressionId.GlobalGet: {

// TODO: this is inefficient because it has to read a string

let global = assert(this.parentFunction.program.elementsByName.get(assert(getGlobalGetName(expr)))!);

assert(global.kind == ElementKind.GLOBAL);

return canConversionOverflow(assert((<Global>global).type), type);

}

case ExpressionId.Binary: {

switch (getBinaryOp(expr)) {

// comparisons do not overflow (result is 0 or 1)

case BinaryOp.EqI32:

case BinaryOp.EqI64:

case BinaryOp.EqF32:

case BinaryOp.EqF64:

case BinaryOp.NeI32:

case BinaryOp.NeI64:

case BinaryOp.NeF32:

case BinaryOp.NeF64:

case BinaryOp.LtI32:

case BinaryOp.LtU32:

case BinaryOp.LtI64:

case BinaryOp.LtU64:

case BinaryOp.LtF32:

case BinaryOp.LtF64:

case BinaryOp.LeI32:

case BinaryOp.LeU32:

case BinaryOp.LeI64:

case BinaryOp.LeU64:

case BinaryOp.LeF32:

case BinaryOp.LeF64:

case BinaryOp.GtI32:

case BinaryOp.GtU32:

case BinaryOp.GtI64:

case BinaryOp.GtU64:

case BinaryOp.GtF32:

case BinaryOp.GtF64:

case BinaryOp.GeI32:

case BinaryOp.GeU32:

case BinaryOp.GeI64:

case BinaryOp.GeU64:

case BinaryOp.GeF32:

case BinaryOp.GeF64: return false;

// result won't overflow if one side is 0 or if one side is 1 and the other wrapped

case BinaryOp.MulI32: {

return !(

(

getExpressionId(operand = getBinaryLeft(expr)) == ExpressionId.Const &&

(

getConstValueI32(operand) == 0 ||

(

getConstValueI32(operand) == 1 &&

!this.canOverflow(getBinaryRight(expr), type)

)

)

) || (

getExpressionId(operand = getBinaryRight(expr)) == ExpressionId.Const &&

(

getConstValueI32(operand) == 0 ||

(

getConstValueI32(operand) == 1 &&

!this.canOverflow(getBinaryLeft(expr), type)

)

)

)

);

}

// result won't overflow if one side is a constant less than this type's mask or one side

// is wrapped

case BinaryOp.AndI32: {

// note that computeSmallIntegerMask returns the mask minus the MSB for signed types

// because signed value garbage bits must be guaranteed to be equal to the MSB.

return !(

(

(

getExpressionId(operand = getBinaryLeft(expr)) == ExpressionId.Const &&

getConstValueI32(operand) <= type.computeSmallIntegerMask(Type.i32)

) || !this.canOverflow(operand, type)

) || (

(

getExpressionId(operand = getBinaryRight(expr)) == ExpressionId.Const &&

getConstValueI32(operand) <= type.computeSmallIntegerMask(Type.i32)

) || !this.canOverflow(operand, type)

)

);

}

// overflows if the shift doesn't clear potential garbage bits

case BinaryOp.ShlI32: {

let shift = 32 - type.size;

return getExpressionId(operand = getBinaryRight(expr)) != ExpressionId.Const

|| getConstValueI32(operand) < shift;

}

// overflows if the value does and the shift doesn't clear potential garbage bits

case BinaryOp.ShrI32: {

let shift = 32 - type.size;

return this.canOverflow(getBinaryLeft(expr), type) && (

getExpressionId(operand = getBinaryRight(expr)) != ExpressionId.Const ||

getConstValueI32(operand) < shift

);

}

// overflows if the shift does not clear potential garbage bits. if an unsigned value is

// wrapped, it can't overflow.

case BinaryOp.ShrU32: {

let shift = 32 - type.size;

return type.is(TypeFlags.SIGNED)

? !(

getExpressionId(operand = getBinaryRight(expr)) == ExpressionId.Const &&

getConstValueI32(operand) > shift // must clear MSB

)

: this.canOverflow(getBinaryLeft(expr), type) && !(

getExpressionId(operand = getBinaryRight(expr)) == ExpressionId.Const &&

getConstValueI32(operand) >= shift // can leave MSB

);

}

// overflows if any side does

case BinaryOp.DivU32:

case BinaryOp.RemI32:

case BinaryOp.RemU32: {

return this.canOverflow(getBinaryLeft(expr), type)

|| this.canOverflow(getBinaryRight(expr), type);

}

}

break;

}

case ExpressionId.Unary: {