Chapter 25: add separate compilation and simplify SSA construction

Introduce Chapter 25 with separately compiled Simple modules, serialized IR,
cross-compilation-unit linking, and native system-library integration.  This
also completes a broad parser and type-system cleanup needed to make graph
construction independent of incomplete parse-time type information.

Separate compilation and linking

- Add compilation-unit Start/Stop nodes and track functions, classes, aliases,
  and global indices across compilation-unit boundaries.
- Serialize canonical types and ideal graph nodes into ELF objects, including
  dependency metadata, relocations, global/local bitset remapping, and dense
  memory-alias information.
- Load dependent objects on demand, recursively resolve source and object
  paths, relink calls and function pointers, and preserve external C symbols.
- Distinguish the post-optimization ownership hook from unknown callers so
  private call graphs can remain precise while public functions remain
  externally callable.
- Add command-line and build support for compiling modules and the reusable
  `sys` object library.

Parser, constructors, and SSA

- Replace inline constructor expansion with a hidden default `<init>` followed
  by an explicit user constructor declared as `new Type = { ... }`.
- Keep the default constructor private, pass private object memory through
  constructor calls, and require user constructors to initialize non-default
  fields before the object escapes.
- Track possibly-uninitialized fields in parser `Var` state and diagnose early
  reads without encoding parser-only constraints in Load and Store nodes.
- Make ordinary parser memory bulk and recover precise alias slices in the
  optimizer using `MemMerge`, `MemPhi`, and `BulkMemPhi` nodes.
- Remove parser-supplied type constraints from Loads and ordinary Phis, defer
  integer/float arithmetic selection, and keep call shape driven by syntax
  instead of provisional inferred types.
- Preserve chained field declarations as static parser information when flow
  types are not yet available, including postfix field updates through calls.

Types, functions, and escape analysis

- Add `TypeScalar` as the common lattice family for integer, float, memory
  pointer, and function-pointer values, with scalar TOP/BOT values for generic
  Loads, Stores, parameters, and invalid intermediate expressions.
- Represent unresolved struct definitions directly with the `TypeStruct`
  forward-reference flag while retaining the separate open-structure concept;
  close and canonicalize recursive structures without side maps.
- Add explicit `FunPtrNode` references so constant function pointers retain a
  graph edge to their Return, and keep referenced functions alive until Opto
  proves the pointer dead.
- Refine public-function and class-initializer escape handling, including
  public-only fallback escape sets and monotone compilation-unit summaries.
- Add guards, proof casts, read-only propagation, pointer-to-integer conversion
  for non-null FFI arguments, and consistent deep mutability checks at calls.

Optimization and code generation

- Make weak and unresolved graph inputs compute conservatively and monotonically
  throughout iterative peepholes and SCCP.
- Preserve independent memory slices when sharpening Stores, retain control on
  conditional Stores, and freeze Store widths from their target field types.
- Extend serialization for new node kinds, scalar types, Store modes, function
  pointers, and memory partitions, preserving serialize/deserialize bijection.
- Complete native selection and encoding support across x86-64, RISC-V, and
  ARM, including FFI pointer conversion and missing integer operations.
- Fix x86 immediate multiply REX encoding and assorted scheduling, register
  allocation, spilling, relocation, and constant-pool issues exposed by the
  larger linked graphs.

System library, tests, and documentation

- Compile and link the Simple `sys` library, including libc bindings, I/O,
  scanners, strings, vectors, array helpers, and executable entry points.
- Add Chapter 25 module, serialization, constructor, forward-reference,
  postfix-update, system, Hello World, and Bubble Sort coverage; update golden
  graphs and spill expectations for the new IR shape.
- Add module and type-system documentation, parser-simplification design notes,
  grammar updates, examples, diagrams, and graph visualization assets.

The resulting compiler passes the raw Chapter 1-24 suite and the Chapter 25
system and separate-compilation tests, including a freshly rebuilt `sys.o` and
the native Bubble Sort example.

1 files changed, 85 insertions, 0 deletions

diff --git a/chapter25/docs/lattice2.gv b/chapter25/docs/lattice2.gv
new file mode 100644
index 00000000..6aa37fa0
--- /dev/null
+++ b/chapter25/docs/lattice2.gv
@@ -0,0 +1,85 @@
+digraph Lattice {
+    compound = true;
+    // Define nodes
+    splines=false;
+    node [shape=oval, style=filled];
+    nodesep=0.2;
+    ranksep=0.4;
+
+    TOP [label="~scalar\n+int+tmp+0", fillcolor=black, fontcolor=white, group=center];
+
+    // ------------------------
+    PTRHQ [label="~tmp\n+tmp+0", fillcolor=green, fontcolor=white, group=left];
+    TOP -> PTRHQ
+
+    VALH_ [label="~nscalar\n+int+tmp", fillcolor=white, group=center];
+    TOP -> VALH_
+
+    INTHQ [label="~int\n+int+0", fillcolor=lightblue, group=right];
+    TOP -> INTHQ
+
+    LEFTHI [label="junk", style=invis, group=junkleft]
+  
+
+    PTRHQ -> LEFTHI-> VALH_ -> INTHQ [style=invis];
+    { rank=same; PTRHQ; LEFTHI; VALH_; INTHQ }
+
+    // ------------------------
+    PTRH_ [label="~ntmp\n+tmp", fillcolor=green, fontcolor=white, group=left];
+    VALH_ -> PTRH_
+    PTRHQ -> PTRH_
+
+    INTH_ [label="~nint\n+int", fillcolor=lightblue, group=right];
+    VALH_ -> INTH_
+    INTHQ -> INTH_
+    { rank=same; PTRH_; INTH_ }
+
+    // ------------------------
+    NILX_ [label="~nil\n[int,tmp]+0", fillcolor=aqua, group=junkleft];
+    INTHQ -> NILX_
+    PTRHQ -> NILX_
+    
+    NIL__ [label="nil\n[+int+tmp],0", fillcolor=pink];
+    VALH_ -> NIL__;
+    
+    NILX_ -> NIL__  [style=invis];
+    { rank=same; NIL__; NILX_ }
+
+    // ------------------------
+    PTRL_ [label="ntmp\ntmp", fillcolor=green, fontcolor=white, group=left];
+    PTRH_ -> PTRL_
+
+    INTL_ [label="nint\nint", fillcolor=lightblue, group=right];
+    INTH_ -> INTL_
+    { rank=same; PTRL_; INTL_ }
+    
+    // ------------------------
+    PTRL0 [label="tmp\ntmp,0", fillcolor=green, fontcolor=white, group=left];
+    PTRL_ -> PTRL0
+    NIL__ -> PTRL0
+
+    VALL_ [label="nscalar\nint,tmp", fillcolor=white, group=center];
+    PTRL_ -> VALL_
+    INTL_ -> VALL_
+    NILX_ -> VALL_
+
+    INTL0 [label="int\nint,0", fillcolor=lightblue, group=right];
+    INTL_ -> INTL0
+    NIL__ -> INTL0
+
+    PTRL0 -> VALL_ -> INTL0 [style=invis];
+    { rank=same; PTRL0; VALL_; INTL0 }
+
+    // ------------------------
+    BOT [label="scalar\nint,tmp,0", fillcolor=black, fontcolor=white, group=center];
+    PTRL0 -> BOT
+    INTL0 -> BOT
+    VALL_ -> BOT
+
+    // ------------------------
+    // Verticle alignment
+    TOP -> VALH_ -> VALL_ -> BOT [style=invis];
+    PTRHQ -> PTRH_ -> PTRL_ -> PTRL0 [style=invis];
+    INTHQ -> INTH_ -> INTL_ -> INTL0 [style=invis];
+    LEFTHI -> NILX_ [style=invis]
+}