stage2: rework the C backend

 * std.ArrayList gains `moveToUnmanaged` and dead code
   `ArrayListUnmanaged.appendWrite` is deleted.
 * emit_h state is attached to Module rather than Compilation.
 * remove the implementation of emit-h because it did not properly
   integrate with incremental compilation. I will re-implement it
   in a follow-up commit.
 * Compilation: use the .codegen_failure tag rather than
   .dependency_failure tag for when `bin_file.updateDecl` fails.

C backend:
 * Use a CValue tagged union instead of strings for C values.
 * Cleanly separate state into Object and DeclGen:
   - Object is present only when generating a .c file
   - DeclGen is present for both generating a .c and .h
 * Move some functions into their respective Object/DeclGen namespace.
 * Forward decls are managed by the incremental compilation frontend; C
   backend no longer renders function signatures based on callsites.
   For simplicity, all functions always get forward decls.
 * Constants are managed by the incremental compilation frontend. C
   backend no longer has a "constants" section.
 * Participate in incremental compilation. Each Decl gets an ArrayList
   for its generated C code and it is updated when the Decl is updated.
   During flush(), all these are joined together in the output file.
 * The new CValue tagged union is used to clean up using of assigning to
   locals without an additional pointer local.
 * Fix bug with bitcast of non-pointers making the memcpy destination
   immutable.

1 files changed, 11 insertions, 8 deletions

diff --git a/src/link.zig b/src/link.zig
index 488f8bf69b..18b093a07a 100644
--- a/src/link.zig
+++ b/src/link.zig
@@ -130,7 +130,7 @@ pub const File = struct {
         elf: Elf.TextBlock,
         coff: Coff.TextBlock,
         macho: MachO.TextBlock,
-        c: void,
+        c: C.DeclBlock,
         wasm: void,
     };
 
@@ -138,7 +138,7 @@ pub const File = struct {
         elf: Elf.SrcFn,
         coff: Coff.SrcFn,
         macho: MachO.SrcFn,
-        c: void,
+        c: C.FnBlock,
         wasm: ?Wasm.FnData,
     };
 
@@ -291,7 +291,7 @@ pub const File = struct {
             .coff => return @fieldParentPtr(Coff, "base", base).updateDecl(module, decl),
             .elf => return @fieldParentPtr(Elf, "base", base).updateDecl(module, decl),
             .macho => return @fieldParentPtr(MachO, "base", base).updateDecl(module, decl),
-            .c => {},
+            .c => return @fieldParentPtr(C, "base", base).updateDecl(module, decl),
             .wasm => return @fieldParentPtr(Wasm, "base", base).updateDecl(module, decl),
         }
     }
@@ -301,7 +301,8 @@ pub const File = struct {
             .coff => return @fieldParentPtr(Coff, "base", base).updateDeclLineNumber(module, decl),
             .elf => return @fieldParentPtr(Elf, "base", base).updateDeclLineNumber(module, decl),
             .macho => return @fieldParentPtr(MachO, "base", base).updateDeclLineNumber(module, decl),
-            .c, .wasm => {},
+            .c => return @fieldParentPtr(C, "base", base).updateDeclLineNumber(module, decl),
+            .wasm => {},
         }
     }
 
@@ -312,7 +313,8 @@ pub const File = struct {
             .coff => return @fieldParentPtr(Coff, "base", base).allocateDeclIndexes(decl),
             .elf => return @fieldParentPtr(Elf, "base", base).allocateDeclIndexes(decl),
             .macho => return @fieldParentPtr(MachO, "base", base).allocateDeclIndexes(decl),
-            .c, .wasm => {},
+            .c => return @fieldParentPtr(C, "base", base).allocateDeclIndexes(decl),
+            .wasm => {},
         }
     }
 
@@ -407,12 +409,13 @@ pub const File = struct {
         }
     }
 
+    /// Called when a Decl is deleted from the Module.
     pub fn freeDecl(base: *File, decl: *Module.Decl) void {
         switch (base.tag) {
             .coff => @fieldParentPtr(Coff, "base", base).freeDecl(decl),
             .elf => @fieldParentPtr(Elf, "base", base).freeDecl(decl),
             .macho => @fieldParentPtr(MachO, "base", base).freeDecl(decl),
-            .c => {},
+            .c => @fieldParentPtr(C, "base", base).freeDecl(decl),
             .wasm => @fieldParentPtr(Wasm, "base", base).freeDecl(decl),
         }
     }
@@ -432,14 +435,14 @@ pub const File = struct {
     pub fn updateDeclExports(
         base: *File,
         module: *Module,
-        decl: *const Module.Decl,
+        decl: *Module.Decl,
         exports: []const *Module.Export,
     ) !void {
         switch (base.tag) {
             .coff => return @fieldParentPtr(Coff, "base", base).updateDeclExports(module, decl, exports),
             .elf => return @fieldParentPtr(Elf, "base", base).updateDeclExports(module, decl, exports),
             .macho => return @fieldParentPtr(MachO, "base", base).updateDeclExports(module, decl, exports),
-            .c => return {},
+            .c => return @fieldParentPtr(C, "base", base).updateDeclExports(module, decl, exports),
             .wasm => return @fieldParentPtr(Wasm, "base", base).updateDeclExports(module, decl, exports),
         }
     }