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, 132 insertions, 0 deletions

diff --git a/chapter25/docs/18-grammar.md b/chapter25/docs/18-grammar.md
new file mode 100644
index 00000000..7b611fbf
--- /dev/null
+++ b/chapter25/docs/18-grammar.md
@@ -0,0 +1,132 @@
+# Grammar for Chapter 16
+
+```antlrv4
+grammar SimpleLanguage;
+
+program : block EOF ;
+
+block : statement+ ;
+
+
+statement
+    : '{' block '}'
+    | returnStatement
+    | ifStatement
+    | whileStatement
+    | breakStatement
+    | continueStatement
+    | metaStatement
+    | structDeclaration
+    | expressionStatement
+    ;
+
+
+returnStatement : 'return' expression ';' ;
+
+ifStatement : 'if' '(' expression ')' statement ('else' statement)? ;
+
+whileStatement : 'while' '(' expression ')' statement ;
+
+breakStatement : 'break' ';' ;
+
+continueStatement : 'continue' ';' ;
+
+metaStatement : '#showGraph' ';' ;
+
+structDeclaration : 'struct' IDENTIFIER '{' block '}'  ;
+
+expressionStatement
+    : type IDENTIFIER ';'
+    | type IDENTIFIER '=' expression ';'
+    |      IDENTIFIER '=' expression ';'
+    |                     expression
+    ;
+
+PRIMTYPE
+    : 'int'
+    | 'i8'
+    | 'i16'
+    | 'i32'
+    | 'i64'
+    | 'u8'
+    | 'u16'
+    | 'u32'
+    | 'flt'
+    | 'f32'
+    | 'f64'
+    | 'bool'
+    ;
+
+type
+    : PRIMTYPE
+    | typeName '?'?
+    | typeName nestedArray+
+    ;
+
+nestedArray : '?'?  '[]'* ;
+
+typeName : IDENTIFIER ;
+
+
+expression : bitWiseExpression ;
+
+bitWiseExpression
+    : comparisonExpression ( '&' | '|' | '^' ) comparisonExpression)*
+    ;
+    
+comparisonExpression
+    : shiftExpression (('==' | '!='| '>'| '<'| '>='| '<=') shiftExpression)*
+    ;
+
+shiftExpression
+    : additiveExpression ( '<<' | '>>>' | '>>' ) additiveExpression)*
+    ;
+    
+additiveExpression
+    : multiplicativeExpression (('+' | '-') multiplicativeExpression)*
+    ;
+
+multiplicativeExpression
+    : unaryExpression (('*' | '/') unaryExpression)*
+    ;
+
+unaryExpression
+    : ('-') unaryExpression
+    | '!' unaryExpression
+    | primaryExpression postAssign
+    ;
+
+primaryExpression
+    : INTEGER_LITERAL
+    | FLOAT_LITERAL
+    | '(' expression ')'
+    | 'true'
+    | 'false'
+    | 'null'
+    | newExpression
+    | IDENTIFIER
+    ;
+
+newExpression 
+    : 'new' IDENTIFIER [ '{' block '}' ]
+    | 'new' IDENTIFIER '[' expression ']'
+    ;
+
+postAssign : postFix [ '=' expression ] | [ '#' ];
+
+postFix
+    : '.' IDENTIFIER      postFix
+    | '[' expression ']'  postFix
+    ;
+
+
+IDENTIFIER : NON_DIGIT (NON_DIGIT | DIGIT)*  ;
+
+INTEGER_LITERAL
+    : [1-9]DIGIT*
+    | [0]
+    ;
+
+NON_DIGIT: [a-zA-Z_];
+DIGIT: [0-9];
+```