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diff --git a/chapter28b/README.md b/chapter28b/README.md index 0a7baa68..008f34d2 100644 --- a/chapter28b/README.md +++ b/chapter28b/README.md @@ -5,8 +5,10 @@ English | [日本語](README.ja.md) [Previous: Chapter 28a](../chapter28a/README.md) The previous chapter compiled every discovered source file together. This -chapter lets a library and other code compile separately, and have full type -information. The client needs the library's *object* file, but not its source. +chapter lets a program and the libraries it uses compile separately, with +full type information. To compile a program that uses a library, we need the +library's *object* file, but not its source. + In spirit this is similar to Java's *class* file, with its full execution and type semantics stored in the file; we happen to be using an ELF file for the same reason. The ahead-of-time compiled code is *also* available for the @@ -14,11 +16,11 @@ linking step. An ordinary native object contains machine code, data, symbols, and relocations. Simple adds a `.simple` section with types and the ideal IR. -Importing `.simple` lets the client check types and optimize calls into the +Importing `.simple` lets the compiler check types and optimize calls into the library. Calls that remain out of line use the library's machine code at native link time. -## A library and a client +## A program that uses a library The runnable example has two separate source roots: @@ -76,7 +78,7 @@ java -ea -cp "build/classes/main:build/classes/test:lib/*" \ src/test/smp/separate/library/Counters.smp ``` -Then compile and evaluate the client using that object: +Then compile and evaluate the program using that object: ```sh java -ea -cp "build/classes/main:build/classes/test:lib/*" \ @@ -88,22 +90,27 @@ java -ea -cp "build/classes/main:build/classes/test:lib/*" \ ## What crosses the separate compilation boundary -The optimized IR owned by the object is compactly encoded in the `.simple` -section and fully reconstructed when read back in. The saved state includes -canonical declarations as well as optimized flow types. E.g. `int x=7` has -declared type `int` and initial value `7`. Struct field types (both declared -and optimized), function argument types (both declared and optimized), numeric -modes, store widths, and source locations also survive serialization. - -Each loaded `.simple` section restores its units into the shared `CompUnit` -tree, mirroring the original code layout. A dependency shared by several -objects uses the same `CompUnit`. Loaded aliases and function indices are -renumbered to avoid collisions; all the dense indices end up in the same -namespace. `GlobalBits` has the mapping from the imported file indices to the -local compilation indices; this remapping extends everywhere through the loaded -code, including recursive types that span several files. Importing skips -parsing the original source, but it still analysed and type checked with its -new callers. +Each source compilation unit gets its own object file: compiling `sys.smp` +produces `sys.o`, `sys/io.o`, `sys/libc.o`, and any other discovered classes. +Mutually dependent sources are compiled together and they output to separate +files with a common build timestamp. + +The object file has a compact encoding of the optimized IR in the `.simple` +section. Declarations and function summaries come first so they can be read +without reading all of the IR. The saved state includes canonical declarations +as well as optimized flow types. E.g. `int x=7` has declared type `int` and +initial value `7`. Struct field types (both declared and optimized), function +argument types (both declared and optimized), numeric modes, store widths, and +source locations also survive serialization. + +Each loaded `.simple` section restores `CompUnit`s into the shared tree, +mirroring the original code layout. A dependency shared by several objects +uses the same `CompUnit`. Loaded aliases and function indices are renumbered +to avoid collisions; all the dense indices end up in the same namespace. +`GlobalBits` has the mapping from the imported file indices to the local +compilation indices; this remapping extends everywhere through the loaded code, +including recursive types that span several files. Importing skips parsing the +original source, but loaded IR is still analyzed within its new context. `ParseAll` is the workhorse that discovers source and object dependencies. It tracks missing symbol references, looking them up in the search path one by one, @@ -117,8 +124,8 @@ compilation phases, including peepholes, Opto and TypeCheck. Dependencies between `CompUnit`s are recorded. An explicitly requested source file is always compiled. Before reusing another local object, `CompUnit` walks -its recorded dependencies and checks every source bundled into each local -object. A missing input or a newer source or dependency object forces parsing +its recorded dependencies and checks each local object's source. +A missing input or a newer source or dependency object forces parsing again, before saved types or IR are imported. This includes transitive dependencies: if A has inlined B, editing B's source invalidates A even while B's object is unchanged. A visited set lets this check follow cycles. @@ -129,33 +136,70 @@ cannot establish their compatibility. These checks are not a complete build driver: explicit requests still compile, and input hashes, compiler/ABI versions, and automatic relinking remain future work. -Loading currently works at the object granularity. Unrelated objects can stay -unloaded, but selecting an object loads its entire saved graph and follows its -recorded dependencies. Future work will look at loading sub-parts more -incrementally. +An unloaded function has a `FunNode`, `SummaryNode`, and `ReturnNode`. Its +summary supplies result, memory, and escape information; calls keep the usual +graph structure without requiring the body. Summaries cannot be inlined. +At an empty optimization worklist, an interesting local call can request its +callee's object using saved size information. The compiler loads the bodies, +reconciles identities, and analyzes them before deciding whether to inline. + +For `sys.io.p`, the compiler can leave `p` out of line without loading `io` IR. +Loading `io.o` makes its functions available, but references inside them carry +types without automatically loading other bodies. An unused imported function +does not cause speculative loading of its callees. Metadata discovery remains +conservative, and a requested object still loads all of its function bodies. + + + +## Using library code and shared state + +The compiler can use library IR to optimize a program while leaving the +library's functions and shared data in their own object files. Separate +compilation must also preserve when each class is initialized, even when +several files use it. + +For example, compiling `helloWorld` may load the body of `sys.io.p` to decide +whether to inline it or not. Inlined code becomes part of `helloWorld.o`. +Ifif it was not inlined that call remains using the function in `sys/io.o`. +Loading did not add another stand-alone copy of `p` to `helloWorld.o`. + +In any case, loaded or not, inlined or not, the initialization semantics of +`sys.io` is unchanged; this means we might need CLInit checks in the inlined +code, or where we load `p` from `sys.io`. +If we did load a bunch of IR, but then chose not to inline, that imported code +is still in our compiled graph. We use `Unlink` before code-gen to remove the +imported bodies. The not-inlined call sites will keep the target names around +for the system linker to eventually connect all the code. +Shared state follows the same idea as function calls. In the earlier example, +all calls within the program use the same `Counters.calls` field. The library +also supplies a shared `$init` flag so its class initializer runs once. +Importing types or loading IR does not run that initializer: execution must +reach a use that needs the class. -## Analysis, ownership, and initialization +A nested class's initializer first ensures that its enclosing class is +initialized, then sets its own flag and runs its body. -An imported function can participate in analysis without belonging to the -client's output. Loading the `io` library, with its `p` print function, means -that `p` is part of the analysis - but when writing out the `helloWorld` app, -`p` will not end up in the `helloWorld.o` file directly. It might be inlined -fully, or called out of line, but there won't be a stand-alone copy of it. +The IR represents an initialization check with a `CLInit` node. Simple saves +this form in the object file so the compiler can analyze it when compiling +a program that uses the library. For machine code, `Lower` turns the check +into a flag test and a conditional call; Eval2 performs the same steps +directly. Optimization can remove a check when the class is +already known to be initialized. -After optimization, `Serialize` saves ideal IR before `Lower` expands class -initialization. `Unlink` then detaches imported bodies for machine compilation -and removes analysis call edges. The client emits its own bodies and any code -copied into them by inlining; the -remaining calls refer to symbols supplied by the library object. +The compiler must also reject cycles in which class initializers depend on one +another. Simple keeps *function summaries* that list calls and classes that +may need initialization, so the compiler can check for cycles before loading +bodies. If a possible cycle appears, it loads all remaining bodies, optimizes, +and checks again. A constant returned by a some other code outside the cycle +can make a branch disappear and remove the cycle. -Class initialization follows the previous chapter's rules. Importing a type -does not initialize its class. Active uses retain `CLInit` checks until -lowering (unless optimization clears them out). The library supplies its -shared class object and flag. Initialization checks appear at all the active-touch -locations, whether local or remote; including source locations for error -reporting. +All required object files must be found before execution. Native code is +linked before the program starts. Eval2 can wait until a call needs a body +to decode its IR, but the object's types and dependencies have already been +read. These choices change when code is prepared; both execution paths use +the same shared state and class-initialization rules. ## Building and checking @@ -168,12 +212,14 @@ make tests CHAPTERS=chapter28b The suite includes the preceding constructor and escape regressions, imported constructors, initialization cycles across objects, shared static data, native -function thunks, and native library/client execution. Make also builds the -modular `sys` object used by the library tests. Clients can import that object -with `-L`; they do not need to parse the standard library's source again. -`IncrementalBuildTest` checks reuse, transitive edits, bundled cycles, missing +function thunks, and native programs linked with libraries. Make also builds +the modular `sys` objects used by the library tests. Programs can import +`sys.o` with `-L`, without parsing the standard library's source again. +`IncrementalBuildTest` checks reuse, transitive edits, cycles across objects, missing inputs, and changed library objects using controlled timestamps. It also compares native execution after an edit with a clean build. +`SelectiveLoadingTest` checks summarized calls, loading for inlining, native +link dependencies, and refinement of a potential initialization cycle. `make release` builds the launcher jar and standard library; `make view` starts the shared graph viewer. |