Chapter 25: Modules, Separate Compilation, and SSA Constructionlinear

Co-authored-by: Hsiang-Ying Fu <66062782+fuhsnn@users.noreply.github.com>
Co-authored-by: fuhsnn <66062782+fuhsnn@users.noreply.github.com>
Co-authored-by: Symious <14933944+symious@users.noreply.github.com>
Co-authored-by: Jun Kawasaki <jun784@gmail.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

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diff --git a/src/main/java/com/seaofnodes/simple/codegen/CompUnit.java b/src/main/java/com/seaofnodes/simple/codegen/CompUnit.java
new file mode 100644
index 00000000..d1326cee
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+++ b/src/main/java/com/seaofnodes/simple/codegen/CompUnit.java
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+package com.seaofnodes.simple.codegen;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeStruct;
+import com.seaofnodes.simple.util.*;
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.*;
+import static com.seaofnodes.simple.codegen.CodeGen.CODE;
+
+// A compilation-unit, which is an external reference and source and object
+// files.  These are mirrored over a file system tree (so form a tree), both
+// the source tree and build/object tree.
+public class CompUnit {
+    public final CompUnit _par;        // Parent, e.g. A/B
+    final String _fname;        // Full slashed file name starting from module root, e.g. A/B/C
+    final public String _cname; // Full dotted class name starting from module root, e.g. A.B.C
+    final String _name;         // Base name, e.g. C
+    final ExternNode _ext;      // Found in external libs; e.g. libc
+    final File _smp;            // Simple source file, e.g. module_root/A/B/C.smp
+    public final File _obj;            // ELF output file, e.g. build/A/B/C.o
+    final public String _src;   // Source code, from file or test case
+    //public Encoding _encoding;  // Encoding for output
+
+    public TypeStruct _clz; // The one TypeStruct being published
+    //BAOS _serial;           // Serialized IR for this ELF file
+    Ary<CompUnit> _deps;    // CompUnits that this CompUnit depends on
+
+    // Per-Compilation-Unit Start/StopNodes, keeping alive all exported Nodes.
+    // Null means no code loaded (yet).
+    public StartCUNode _start;
+    public StopCUNode  _stop ;
+
+
+    // Discovered source file.  Source is loaded if required to parse, and null
+    // otherwise.
+    CompUnit( CompUnit par, String fname, String cname, String name ) throws IOException {
+        _par  = par;
+        _fname= fname;
+        _cname= cname;
+        _name = name;
+        _ext  = null;
+        _smp  = new File( CODE.  _modDir + "/" + fname + ".smp");
+        _obj  = new File( CODE._buildDir + "/" + fname + ".o"  );
+
+        boolean mustCompile = _smp.exists() && // Has source to compile
+            ( !_obj.exists() ||                // No object file
+              _smp.lastModified() > _obj.lastModified() || // Out-of-date with source?
+              checkDependentObjs() );                      // Out-of-date with other objs?
+        _src  = mustCompile ? new String(Files.readAllBytes(_smp.toPath())) : null;
+    }
+
+    // Test case.  No source file.  Source code passed in as a String.  Fake
+    // class name.
+    CompUnit( String fname, String src ) {
+        _par  = null;
+        _name = fname;
+        _fname= fname;
+        _cname= fname;
+        _ext  = null;
+        _smp  = null;
+        _obj  = null;
+        _src  = src;
+    }
+
+    // External CompUnit, pulled in from an external library like libc
+    CompUnit( ExternNode ext, String symbol ) {
+        _par  = null;
+        _name = symbol;
+        _fname= _name;
+        _cname= null;
+        _ext  = ext;
+        _smp  = null;
+        _obj  = null;
+        _src  = null;
+    }
+
+    // External Simple object file, or namespace parent, found on an external search path.
+    CompUnit( File obj, CompUnit par, String fname, String cname, String name ) {
+        _par  = par;
+        _name = name;
+        _fname= fname;
+        _cname= cname;
+        _ext  = null;
+        _smp  = null;
+        _obj  = obj;
+        _src  = null;
+    }
+
+    // Return true if _obj is out-of-date relative to dependents.
+    private boolean checkDependentObjs() {
+        ElfReader elf = CODE.getElf(_obj);
+        elf.loadPublicSymbols();
+        for( String dep : elf._deps ) {
+            File obj = new File(CODE._buildDir+"/"+dep+".o");
+            if( obj.lastModified() > _obj.lastModified() ) // Out-of-date with deps?
+                return true;
+        }
+        return false;
+    }
+
+    // Add a discovered dependency, for later writing out in an ELF file, ".simple" section
+    void addDep(CompUnit dep) {
+        if( _deps == null ) _deps = new Ary<>(CompUnit.class);
+        _deps.add(dep);
+    }
+
+    public void addFun(CodeGen code, FunNode fun) {
+        assert fun.in(1)==_start;
+        _stop.addDef(fun.ret());
+        code.add(_stop);
+        _stop.addDep(fun);
+    }
+
+    void setStart(CodeGen code) {
+        _stop  = new  StopCUNode().init();
+        _start = new StartCUNode(code._start,_stop, Type.BOTTOM, _fname).init();
+        code._stop.addDef(_stop);
+    }
+
+
+    @Override public String toString() {
+        String x = "{"+_cname;
+        if( _smp!=null && _smp.exists()) x += ",hasSMP";
+        if( _obj!=null && _obj.exists()) x += ",hasObj";
+        if( _src!=null   ) x += ",hasSrc";
+        if( _ext != null ) x += ",isExt";
+        x += "}";
+        return x;
+    }
+}