stage2: detection of comptime array literals

Introduce `validate_array_init_comptime`, similar to
`validate_struct_init_comptime` introduced in
713d2a9b3883942491b40738245232680877cc66.

`zirValidateArrayInit` is improved to detect comptime array literals and
emit AIR accordingly. This code is very similar to the changes
introduced in that same commit for `zirValidateStructInit`.

The C backend needed some improvements to continue passing the same set
of tests:
 * `resolveInst` for arrays now will add a local `static const` with the
   array value and so then `elem_val` instructions reference that local.
   It memoizes accesses using `value_map`, which is changed to use
   `Air.Inst.Ref` as the key rather than `Air.Inst.Index`.
 * This required a mechanism for writing to a "header" which is lines
   that appear at the beginning of a function body, before everything
   else.
 * dbg_stmt output comments rather than `#line` directives.
   TODO comment reproduced here:

We need to re-evaluate whether to emit these or not. If we naively emit
these directives, the output file will report bogus line numbers because
every newline after the #line directive adds one to the line.
We also don't print the filename yet, so the output is strictly unhelpful.
If we wanted to go this route, we would need to go all the way and not output
newlines until the next dbg_stmt occurs.
Perhaps an additional compilation option is in order?

`Value.elemValue` is improved to support `elem_ptr` values.

1 files changed, 64 insertions, 12 deletions

diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index 05ec1b1a88..58bf919b1f 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -44,7 +44,7 @@ const BlockData = struct {
     result: CValue,
 };
 
-pub const CValueMap = std.AutoHashMap(Air.Inst.Index, CValue);
+pub const CValueMap = std.AutoHashMap(Air.Inst.Ref, CValue);
 pub const TypedefMap = std.ArrayHashMap(
     Type,
     struct { name: []const u8, rendered: []u8 },
@@ -110,11 +110,29 @@ pub const Function = struct {
     func: *Module.Fn,
 
     fn resolveInst(f: *Function, inst: Air.Inst.Ref) !CValue {
-        if (f.air.value(inst)) |_| {
-            return CValue{ .constant = inst };
+        const gop = try f.value_map.getOrPut(inst);
+        if (gop.found_existing) return gop.value_ptr.*;
+
+        const val = f.air.value(inst).?;
+        const ty = f.air.typeOf(inst);
+        switch (ty.zigTypeTag()) {
+            .Array => {
+                const writer = f.object.code_header.writer();
+                const decl_c_value = f.allocLocalValue();
+                gop.value_ptr.* = decl_c_value;
+                try writer.writeAll("static ");
+                try f.object.dg.renderTypeAndName(writer, ty, decl_c_value, .Const);
+                try writer.writeAll(" = ");
+                try f.object.dg.renderValue(writer, ty, val);
+                try writer.writeAll(";\n ");
+                return decl_c_value;
+            },
+            else => {
+                const result = CValue{ .constant = inst };
+                gop.value_ptr.* = result;
+                return result;
+            },
         }
-        const index = Air.refToIndex(inst).?;
-        return f.value_map.get(index).?; // Assertion means instruction does not dominate usage.
     }
 
     fn allocLocalValue(f: *Function) CValue {
@@ -154,6 +172,8 @@ pub const Function = struct {
 pub const Object = struct {
     dg: DeclGen,
     code: std.ArrayList(u8),
+    /// Goes before code. Initialized and deinitialized in `genFunc`.
+    code_header: std.ArrayList(u8) = undefined,
     indent_writer: IndentWriter(std.ArrayList(u8).Writer),
 
     fn writer(o: *Object) IndentWriter(std.ArrayList(u8).Writer).Writer {
@@ -218,12 +238,18 @@ pub const DeclGen = struct {
             // Determine if we must pointer cast.
             if (ty.eql(decl.ty)) {
                 try writer.writeByte('&');
-            } else {
-                try writer.writeAll("(");
-                try dg.renderType(writer, ty);
-                try writer.writeAll(")&");
+                try dg.renderDeclName(decl, writer);
+                return;
             }
+
+            try writer.writeAll("((");
+            try dg.renderType(writer, ty);
+            try writer.writeAll(")&");
+            try dg.renderDeclName(decl, writer);
+            try writer.writeByte(')');
+            return;
         }
+
         try dg.renderDeclName(decl, writer);
     }
 
@@ -1010,6 +1036,10 @@ pub fn genFunc(f: *Function) !void {
     defer tracy.end();
 
     const o = &f.object;
+
+    o.code_header = std.ArrayList(u8).init(f.object.dg.gpa);
+    defer o.code_header.deinit();
+
     const is_global = o.dg.module.decl_exports.contains(f.func.owner_decl);
     const fwd_decl_writer = o.dg.fwd_decl.writer();
     if (is_global) {
@@ -1020,12 +1050,26 @@ pub fn genFunc(f: *Function) !void {
 
     try o.indent_writer.insertNewline();
     try o.dg.renderFunctionSignature(o.writer(), is_global);
-
     try o.writer().writeByte(' ');
+
+    // In case we need to use the header, populate it with a copy of the function
+    // signature here. We anticipate a brace, newline, and space.
+    try o.code_header.ensureUnusedCapacity(o.code.items.len + 3);
+    o.code_header.appendSliceAssumeCapacity(o.code.items);
+    o.code_header.appendSliceAssumeCapacity("{\n ");
+    const empty_header_len = o.code_header.items.len;
+
     const main_body = f.air.getMainBody();
     try genBody(f, main_body);
 
     try o.indent_writer.insertNewline();
+
+    // If we have a header to insert, append the body to the header
+    // and then return the result, freeing the body.
+    if (o.code_header.items.len > empty_header_len) {
+        try o.code_header.appendSlice(o.code.items[empty_header_len..]);
+        mem.swap(std.ArrayList(u8), &o.code, &o.code_header);
+    }
 }
 
 pub fn genDecl(o: *Object) !void {
@@ -1289,7 +1333,7 @@ fn genBody(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail, OutO
         };
         switch (result_value) {
             .none => {},
-            else => try f.value_map.putNoClobber(inst, result_value),
+            else => try f.value_map.putNoClobber(Air.indexToRef(inst), result_value),
         }
     }
 
@@ -2189,7 +2233,15 @@ fn airCall(f: *Function, inst: Air.Inst.Index) !CValue {
 fn airDbgStmt(f: *Function, inst: Air.Inst.Index) !CValue {
     const dbg_stmt = f.air.instructions.items(.data)[inst].dbg_stmt;
     const writer = f.object.writer();
-    try writer.print("#line {d}\n", .{dbg_stmt.line + 1});
+    // TODO re-evaluate whether to emit these or not. If we naively emit
+    // these directives, the output file will report bogus line numbers because
+    // every newline after the #line directive adds one to the line.
+    // We also don't print the filename yet, so the output is strictly unhelpful.
+    // If we wanted to go this route, we would need to go all the way and not output
+    // newlines until the next dbg_stmt occurs.
+    // Perhaps an additional compilation option is in order?
+    //try writer.print("#line {d}\n", .{dbg_stmt.line + 1});
+    try writer.print("/* file:{d}:{d} */\n", .{ dbg_stmt.line + 1, dbg_stmt.column + 1 });
     return CValue.none;
 }