79 lines
2.2 KiB
C++
79 lines
2.2 KiB
C++
// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
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#pragma once
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#include "Luau/NotNull.h"
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#include "Luau/TypedAllocator.h"
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#include "Luau/Variant.h"
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namespace Luau
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{
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using Def = Variant<struct Undefined, struct Phi>;
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/**
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* We statically approximate a value at runtime using a symbolic value, which we call a Def.
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*
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* DataFlowGraphBuilder will allocate these defs as a stand-in for some Luau values, and bind them to places that
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* can hold a Luau value, and then observes how those defs will commute as it statically evaluate the program.
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*
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* It must also be noted that defs are a cyclic graph, so it is not safe to recursively traverse into it expecting it to terminate.
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*/
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using DefId = NotNull<const Def>;
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/**
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* A "single-object" value.
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*
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* Leaky implementation note: sometimes "multiple-object" values, but none of which were interesting enough to warrant creating a phi node instead.
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* That can happen because there's no point in creating a phi node that points to either resultant in `if math.random() > 0.5 then 5 else "hello"`.
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* This might become of utmost importance if we wanted to do some backward reasoning, e.g. if `5` is taken, then `cond` must be `truthy`.
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*/
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struct Undefined
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{
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};
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/**
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* A phi node is a union of defs.
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*
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* We need this because we're statically evaluating a program, and sometimes a place may be assigned with
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* different defs, and when that happens, we need a special data type that merges in all the defs
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* that will flow into that specific place. For example, consider this simple program:
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*
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* ```
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* x-1
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* if cond() then
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* x-2 = 5
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* else
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* x-3 = "hello"
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* end
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* x-4 : {x-2, x-3}
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* ```
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*
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* At x-4, we know for a fact statically that either `5` or `"hello"` can flow into the variable `x` after the branch, but
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* we cannot make any definitive decisions about which one, so we just take in both.
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*/
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struct Phi
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{
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std::vector<DefId> operands;
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};
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template<typename T>
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T* getMutable(DefId def)
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{
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return get_if<T>(def.get());
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}
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template<typename T>
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const T* get(DefId def)
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{
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return getMutable<T>(def);
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}
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struct DefArena
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{
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TypedAllocator<Def> allocator;
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DefId freshDef();
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};
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} // namespace Luau
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