Merge remote-tracking branch 'origin/master' into llvm12

Conflicts:
 * src/clang.zig
 * src/llvm.zig
   - this file got moved to src/llvm/bindings.zig in master branch so I
     had to put the new LLVM arch/os enum tags into it.
 * lib/std/target.zig, src/stage1/target.cpp
   - haiku had an inconsistency with its default target ABI, gnu vs
     eabi. In this commit we make it gnu in both places to match the
     latest changes by @hoanga.
 * src/translate_c.zig

1 files changed, 757 insertions, 238 deletions

diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index e562ce320e..a885b984ac 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -1,312 +1,774 @@
 const std = @import("std");
+const assert = std.debug.assert;
+const mem = std.mem;
+const log = std.log.scoped(.c);
 
 const link = @import("../link.zig");
 const Module = @import("../Module.zig");
-
-const Inst = @import("../ir.zig").Inst;
+const Compilation = @import("../Compilation.zig");
+const ir = @import("../ir.zig");
+const Inst = ir.Inst;
 const Value = @import("../value.zig").Value;
 const Type = @import("../type.zig").Type;
-
+const TypedValue = @import("../TypedValue.zig");
 const C = link.File.C;
 const Decl = Module.Decl;
-const mem = std.mem;
+const trace = @import("../tracy.zig").trace;
 
-const indentation = "    ";
+const Mutability = enum { Const, Mut };
 
-/// Maps a name from Zig source to C. Currently, this will always give the same
-/// output for any given input, sometimes resulting in broken identifiers.
-fn map(allocator: *std.mem.Allocator, name: []const u8) ![]const u8 {
-    return allocator.dupe(u8, name);
-}
+pub const CValue = union(enum) {
+    none: void,
+    /// Index into local_names
+    local: usize,
+    /// Index into local_names, but take the address.
+    local_ref: usize,
+    /// A constant instruction, to be rendered inline.
+    constant: *Inst,
+    /// Index into the parameters
+    arg: usize,
+    /// By-value
+    decl: *Decl,
+};
 
-fn renderType(ctx: *Context, writer: std.ArrayList(u8).Writer, T: Type) !void {
-    switch (T.zigTypeTag()) {
-        .NoReturn => {
-            try writer.writeAll("zig_noreturn void");
-        },
-        .Void => try writer.writeAll("void"),
-        .Int => {
-            if (T.tag() == .u8) {
-                ctx.file.need_stdint = true;
-                try writer.writeAll("uint8_t");
-            } else if (T.tag() == .usize) {
-                ctx.file.need_stddef = true;
-                try writer.writeAll("size_t");
-            } else {
-                return ctx.file.fail(ctx.decl.src(), "TODO implement int types", .{});
-            }
-        },
-        else => |e| return ctx.file.fail(ctx.decl.src(), "TODO implement type {}", .{e}),
+pub const CValueMap = std.AutoHashMap(*Inst, CValue);
+
+/// This data is available when outputting .c code for a Module.
+/// It is not available when generating .h file.
+pub const Object = struct {
+    dg: DeclGen,
+    gpa: *mem.Allocator,
+    code: std.ArrayList(u8),
+    value_map: CValueMap,
+    next_arg_index: usize = 0,
+    next_local_index: usize = 0,
+    next_block_index: usize = 0,
+    indent_writer: IndentWriter(std.ArrayList(u8).Writer),
+
+    fn resolveInst(o: *Object, inst: *Inst) !CValue {
+        if (inst.value()) |_| {
+            return CValue{ .constant = inst };
+        }
+        return o.value_map.get(inst).?; // Instruction does not dominate all uses!
     }
-}
 
-fn renderValue(ctx: *Context, writer: std.ArrayList(u8).Writer, T: Type, val: Value) !void {
-    switch (T.zigTypeTag()) {
-        .Int => {
-            if (T.isSignedInt())
-                return writer.print("{}", .{val.toSignedInt()});
-            return writer.print("{}", .{val.toUnsignedInt()});
-        },
-        else => |e| return ctx.file.fail(ctx.decl.src(), "TODO implement value {}", .{e}),
+    fn allocLocalValue(o: *Object) CValue {
+        const result = o.next_local_index;
+        o.next_local_index += 1;
+        return .{ .local = result };
     }
-}
 
-fn renderFunctionSignature(ctx: *Context, writer: std.ArrayList(u8).Writer, decl: *Decl) !void {
-    const tv = decl.typed_value.most_recent.typed_value;
-    try renderType(ctx, writer, tv.ty.fnReturnType());
-    // Use the child allocator directly, as we know the name can be freed before
-    // the rest of the arena.
-    const name = try map(ctx.arena.child_allocator, mem.spanZ(decl.name));
-    defer ctx.arena.child_allocator.free(name);
-    try writer.print(" {}(", .{name});
-    var param_len = tv.ty.fnParamLen();
-    if (param_len == 0)
-        try writer.writeAll("void")
-    else {
-        var index: usize = 0;
-        while (index < param_len) : (index += 1) {
-            if (index > 0) {
-                try writer.writeAll(", ");
-            }
-            try renderType(ctx, writer, tv.ty.fnParamType(index));
-            try writer.print(" arg{}", .{index});
-        }
+    fn allocLocal(o: *Object, ty: Type, mutability: Mutability) !CValue {
+        const local_value = o.allocLocalValue();
+        try o.renderTypeAndName(o.writer(), ty, local_value, mutability);
+        return local_value;
     }
-    try writer.writeByte(')');
-}
 
-pub fn generate(file: *C, decl: *Decl) !void {
-    switch (decl.typed_value.most_recent.typed_value.ty.zigTypeTag()) {
-        .Fn => try genFn(file, decl),
-        .Array => try genArray(file, decl),
-        else => |e| return file.fail(decl.src(), "TODO {}", .{e}),
+    fn writer(o: *Object) IndentWriter(std.ArrayList(u8).Writer).Writer {
+        return o.indent_writer.writer();
     }
-}
 
-fn genArray(file: *C, decl: *Decl) !void {
-    const tv = decl.typed_value.most_recent.typed_value;
-    // TODO: prevent inline asm constants from being emitted
-    const name = try map(file.base.allocator, mem.span(decl.name));
-    defer file.base.allocator.free(name);
-    if (tv.val.cast(Value.Payload.Bytes)) |payload|
-        if (tv.ty.sentinel()) |sentinel|
-            if (sentinel.toUnsignedInt() == 0)
-                // TODO: static by default
-                try file.constants.writer().print("const char *const {} = \"{}\";\n", .{ name, payload.data })
-            else
-                return file.fail(decl.src(), "TODO byte arrays with non-zero sentinels", .{})
-        else
-            return file.fail(decl.src(), "TODO byte arrays without sentinels", .{})
-    else
-        return file.fail(decl.src(), "TODO non-byte arrays", .{});
-}
+    fn writeCValue(o: *Object, w: anytype, c_value: CValue) !void {
+        switch (c_value) {
+            .none => unreachable,
+            .local => |i| return w.print("t{d}", .{i}),
+            .local_ref => |i| return w.print("&t{d}", .{i}),
+            .constant => |inst| return o.dg.renderValue(w, inst.ty, inst.value().?),
+            .arg => |i| return w.print("a{d}", .{i}),
+            .decl => |decl| return w.writeAll(mem.span(decl.name)),
+        }
+    }
+
+    fn renderTypeAndName(
+        o: *Object,
+        w: anytype,
+        ty: Type,
+        name: CValue,
+        mutability: Mutability,
+    ) error{ OutOfMemory, AnalysisFail }!void {
+        var suffix = std.ArrayList(u8).init(o.gpa);
+        defer suffix.deinit();
+
+        var render_ty = ty;
+        while (render_ty.zigTypeTag() == .Array) {
+            const sentinel_bit = @boolToInt(render_ty.sentinel() != null);
+            const c_len = render_ty.arrayLen() + sentinel_bit;
+            try suffix.writer().print("[{d}]", .{c_len});
+            render_ty = render_ty.elemType();
+        }
+
+        try o.dg.renderType(w, render_ty);
 
-const Context = struct {
-    file: *C,
+        const const_prefix = switch (mutability) {
+            .Const => "const ",
+            .Mut => "",
+        };
+        try w.print(" {s}", .{const_prefix});
+        try o.writeCValue(w, name);
+        try w.writeAll(suffix.items);
+    }
+};
+
+/// This data is available both when outputting .c code and when outputting an .h file.
+pub const DeclGen = struct {
+    module: *Module,
     decl: *Decl,
-    inst_map: *std.AutoHashMap(*Inst, []u8),
-    arena: *std.heap.ArenaAllocator,
-    argdex: usize = 0,
-    unnamed_index: usize = 0,
-
-    fn resolveInst(self: *Context, inst: *Inst) ![]u8 {
-        if (inst.cast(Inst.Constant)) |const_inst| {
-            var out = std.ArrayList(u8).init(&self.arena.allocator);
-            try renderValue(self, out.writer(), inst.ty, const_inst.val);
-            return out.toOwnedSlice();
+    fwd_decl: std.ArrayList(u8),
+    error_msg: ?*Module.ErrorMsg,
+
+    fn fail(dg: *DeclGen, src: usize, comptime format: []const u8, args: anytype) error{ AnalysisFail, OutOfMemory } {
+        dg.error_msg = try Module.ErrorMsg.create(dg.module.gpa, .{
+            .file_scope = dg.decl.getFileScope(),
+            .byte_offset = src,
+        }, format, args);
+        return error.AnalysisFail;
+    }
+
+    fn renderValue(
+        dg: *DeclGen,
+        writer: anytype,
+        t: Type,
+        val: Value,
+    ) error{ OutOfMemory, AnalysisFail }!void {
+        if (val.isUndef()) {
+            return dg.fail(dg.decl.src(), "TODO: C backend: properly handle undefined in all cases (with debug safety?)", .{});
         }
-        if (self.inst_map.get(inst)) |val| {
-            return val;
+        switch (t.zigTypeTag()) {
+            .Int => {
+                if (t.isSignedInt())
+                    return writer.print("{d}", .{val.toSignedInt()});
+                return writer.print("{d}", .{val.toUnsignedInt()});
+            },
+            .Pointer => switch (val.tag()) {
+                .undef, .zero => try writer.writeAll("0"),
+                .one => try writer.writeAll("1"),
+                .decl_ref => {
+                    const decl = val.castTag(.decl_ref).?.data;
+
+                    // Determine if we must pointer cast.
+                    const decl_tv = decl.typed_value.most_recent.typed_value;
+                    if (t.eql(decl_tv.ty)) {
+                        try writer.print("&{s}", .{decl.name});
+                    } else {
+                        try writer.writeAll("(");
+                        try dg.renderType(writer, t);
+                        try writer.print(")&{s}", .{decl.name});
+                    }
+                },
+                .function => {
+                    const func = val.castTag(.function).?.data;
+                    try writer.print("{s}", .{func.owner_decl.name});
+                },
+                .extern_fn => {
+                    const decl = val.castTag(.extern_fn).?.data;
+                    try writer.print("{s}", .{decl.name});
+                },
+                else => |e| return dg.fail(
+                    dg.decl.src(),
+                    "TODO: C backend: implement Pointer value {s}",
+                    .{@tagName(e)},
+                ),
+            },
+            .Array => {
+                // First try specific tag representations for more efficiency.
+                switch (val.tag()) {
+                    .undef, .empty_struct_value, .empty_array => try writer.writeAll("{}"),
+                    .bytes => {
+                        const bytes = val.castTag(.bytes).?.data;
+                        // TODO: make our own C string escape instead of using std.zig.fmtEscapes
+                        try writer.print("\"{}\"", .{std.zig.fmtEscapes(bytes)});
+                    },
+                    else => {
+                        // Fall back to generic implementation.
+                        var arena = std.heap.ArenaAllocator.init(dg.module.gpa);
+                        defer arena.deinit();
+
+                        try writer.writeAll("{");
+                        var index: usize = 0;
+                        const len = t.arrayLen();
+                        const elem_ty = t.elemType();
+                        while (index < len) : (index += 1) {
+                            if (index != 0) try writer.writeAll(",");
+                            const elem_val = try val.elemValue(&arena.allocator, index);
+                            try dg.renderValue(writer, elem_ty, elem_val);
+                        }
+                        if (t.sentinel()) |sentinel_val| {
+                            if (index != 0) try writer.writeAll(",");
+                            try dg.renderValue(writer, elem_ty, sentinel_val);
+                        }
+                        try writer.writeAll("}");
+                    },
+                }
+            },
+            .Bool => return writer.print("{}", .{val.toBool()}),
+            else => |e| return dg.fail(dg.decl.src(), "TODO: C backend: implement value {s}", .{
+                @tagName(e),
+            }),
+        }
+    }
+
+    fn renderFunctionSignature(dg: *DeclGen, w: anytype, is_global: bool) !void {
+        if (!is_global) {
+            try w.writeAll("static ");
+        }
+        const tv = dg.decl.typed_value.most_recent.typed_value;
+        try dg.renderType(w, tv.ty.fnReturnType());
+        const decl_name = mem.span(dg.decl.name);
+        try w.print(" {s}(", .{decl_name});
+        var param_len = tv.ty.fnParamLen();
+        if (param_len == 0)
+            try w.writeAll("void")
+        else {
+            var index: usize = 0;
+            while (index < param_len) : (index += 1) {
+                if (index > 0) {
+                    try w.writeAll(", ");
+                }
+                try dg.renderType(w, tv.ty.fnParamType(index));
+                try w.print(" a{d}", .{index});
+            }
         }
-        unreachable;
+        try w.writeByte(')');
     }
 
-    fn name(self: *Context) ![]u8 {
-        const val = try std.fmt.allocPrint(&self.arena.allocator, "__temp_{}", .{self.unnamed_index});
-        self.unnamed_index += 1;
-        return val;
+    fn renderType(dg: *DeclGen, w: anytype, t: Type) error{ OutOfMemory, AnalysisFail }!void {
+        switch (t.zigTypeTag()) {
+            .NoReturn => {
+                try w.writeAll("zig_noreturn void");
+            },
+            .Void => try w.writeAll("void"),
+            .Bool => try w.writeAll("bool"),
+            .Int => {
+                switch (t.tag()) {
+                    .u8 => try w.writeAll("uint8_t"),
+                    .i8 => try w.writeAll("int8_t"),
+                    .u16 => try w.writeAll("uint16_t"),
+                    .i16 => try w.writeAll("int16_t"),
+                    .u32 => try w.writeAll("uint32_t"),
+                    .i32 => try w.writeAll("int32_t"),
+                    .u64 => try w.writeAll("uint64_t"),
+                    .i64 => try w.writeAll("int64_t"),
+                    .usize => try w.writeAll("uintptr_t"),
+                    .isize => try w.writeAll("intptr_t"),
+                    .c_short => try w.writeAll("short"),
+                    .c_ushort => try w.writeAll("unsigned short"),
+                    .c_int => try w.writeAll("int"),
+                    .c_uint => try w.writeAll("unsigned int"),
+                    .c_long => try w.writeAll("long"),
+                    .c_ulong => try w.writeAll("unsigned long"),
+                    .c_longlong => try w.writeAll("long long"),
+                    .c_ulonglong => try w.writeAll("unsigned long long"),
+                    .int_signed, .int_unsigned => {
+                        const info = t.intInfo(dg.module.getTarget());
+                        const sign_prefix = switch (info.signedness) {
+                            .signed => "",
+                            .unsigned => "u",
+                        };
+                        inline for (.{ 8, 16, 32, 64, 128 }) |nbits| {
+                            if (info.bits <= nbits) {
+                                try w.print("{s}int{d}_t", .{ sign_prefix, nbits });
+                                break;
+                            }
+                        } else {
+                            return dg.fail(dg.decl.src(), "TODO: C backend: implement integer types larger than 128 bits", .{});
+                        }
+                    },
+                    else => unreachable,
+                }
+            },
+            .Pointer => {
+                if (t.isSlice()) {
+                    return dg.fail(dg.decl.src(), "TODO: C backend: implement slices", .{});
+                } else {
+                    try dg.renderType(w, t.elemType());
+                    try w.writeAll(" *");
+                    if (t.isConstPtr()) {
+                        try w.writeAll("const ");
+                    }
+                    if (t.isVolatilePtr()) {
+                        try w.writeAll("volatile ");
+                    }
+                }
+            },
+            .Array => {
+                try dg.renderType(w, t.elemType());
+                try w.writeAll(" *");
+            },
+            .Null, .Undefined => unreachable, // must be const or comptime
+            else => |e| return dg.fail(dg.decl.src(), "TODO: C backend: implement type {s}", .{
+                @tagName(e),
+            }),
+        }
     }
 
-    fn deinit(self: *Context) void {
-        self.* = undefined;
+    fn functionIsGlobal(dg: *DeclGen, tv: TypedValue) bool {
+        switch (tv.val.tag()) {
+            .extern_fn => return true,
+            .function => {
+                const func = tv.val.castTag(.function).?.data;
+                return dg.module.decl_exports.contains(func.owner_decl);
+            },
+            else => unreachable,
+        }
     }
 };
 
-fn genFn(file: *C, decl: *Decl) !void {
-    const writer = file.main.writer();
-    const tv = decl.typed_value.most_recent.typed_value;
-
-    var arena = std.heap.ArenaAllocator.init(file.base.allocator);
-    defer arena.deinit();
-    var inst_map = std.AutoHashMap(*Inst, []u8).init(&arena.allocator);
-    defer inst_map.deinit();
-    var ctx = Context{
-        .file = file,
-        .decl = decl,
-        .arena = &arena,
-        .inst_map = &inst_map,
-    };
-    defer ctx.deinit();
-
-    try renderFunctionSignature(&ctx, writer, decl);
-
-    try writer.writeAll(" {");
-
-    const func: *Module.Fn = tv.val.cast(Value.Payload.Function).?.func;
-    const instructions = func.analysis.success.instructions;
-    if (instructions.len > 0) {
-        try writer.writeAll("\n");
-        for (instructions) |inst| {
-            if (switch (inst.tag) {
-                .assembly => try genAsm(&ctx, inst.castTag(.assembly).?),
-                .call => try genCall(&ctx, inst.castTag(.call).?),
-                .add => try genBinOp(&ctx, inst.cast(Inst.BinOp).?, "+"),
-                .sub => try genBinOp(&ctx, inst.cast(Inst.BinOp).?, "-"),
-                .ret => try genRet(&ctx, inst.castTag(.ret).?),
-                .retvoid => try genRetVoid(&ctx),
-                .arg => try genArg(&ctx),
-                .dbg_stmt => try genDbgStmt(&ctx, inst.castTag(.dbg_stmt).?),
-                .breakpoint => try genBreak(&ctx, inst.castTag(.breakpoint).?),
-                .unreach => try genUnreach(&ctx, inst.castTag(.unreach).?),
-                .intcast => try genIntCast(&ctx, inst.castTag(.intcast).?),
-                else => |e| return file.fail(decl.src(), "TODO implement C codegen for {}", .{e}),
-            }) |name| {
-                try ctx.inst_map.putNoClobber(inst, name);
+pub fn genDecl(o: *Object) !void {
+    const tracy = trace(@src());
+    defer tracy.end();
+
+    const tv = o.dg.decl.typed_value.most_recent.typed_value;
+
+    if (tv.val.castTag(.function)) |func_payload| {
+        const is_global = o.dg.functionIsGlobal(tv);
+        const fwd_decl_writer = o.dg.fwd_decl.writer();
+        if (is_global) {
+            try fwd_decl_writer.writeAll("ZIG_EXTERN_C ");
+        }
+        try o.dg.renderFunctionSignature(fwd_decl_writer, is_global);
+        try fwd_decl_writer.writeAll(";\n");
+
+        const func: *Module.Fn = func_payload.data;
+        try o.indent_writer.insertNewline();
+        try o.dg.renderFunctionSignature(o.writer(), is_global);
+
+        try o.writer().writeByte(' ');
+        try genBody(o, func.body);
+
+        try o.indent_writer.insertNewline();
+    } else if (tv.val.tag() == .extern_fn) {
+        const writer = o.writer();
+        try writer.writeAll("ZIG_EXTERN_C ");
+        try o.dg.renderFunctionSignature(writer, true);
+        try writer.writeAll(";\n");
+    } else {
+        const writer = o.writer();
+        try writer.writeAll("static ");
+
+        // TODO ask the Decl if it is const
+        // https://github.com/ziglang/zig/issues/7582
+
+        const decl_c_value: CValue = .{ .decl = o.dg.decl };
+        try o.renderTypeAndName(writer, tv.ty, decl_c_value, .Mut);
+
+        try writer.writeAll(" = ");
+        try o.dg.renderValue(writer, tv.ty, tv.val);
+        try writer.writeAll(";\n");
+    }
+}
+
+pub fn genHeader(dg: *DeclGen) error{ AnalysisFail, OutOfMemory }!void {
+    const tracy = trace(@src());
+    defer tracy.end();
+
+    const tv = dg.decl.typed_value.most_recent.typed_value;
+    const writer = dg.fwd_decl.writer();
+
+    switch (tv.ty.zigTypeTag()) {
+        .Fn => {
+            const is_global = dg.functionIsGlobal(tv);
+            if (is_global) {
+                try writer.writeAll("ZIG_EXTERN_C ");
             }
+            try dg.renderFunctionSignature(writer, is_global);
+            try dg.fwd_decl.appendSlice(";\n");
+        },
+        else => {},
+    }
+}
+
+pub fn genBody(o: *Object, body: ir.Body) error{ AnalysisFail, OutOfMemory }!void {
+    const writer = o.writer();
+    if (body.instructions.len == 0) {
+        try writer.writeAll("{}");
+        return;
+    }
+
+    try writer.writeAll("{\n");
+    o.indent_writer.pushIndent();
+
+    for (body.instructions) |inst| {
+        const result_value = switch (inst.tag) {
+            .constant => unreachable, // excluded from function bodies
+            .add => try genBinOp(o, inst.castTag(.add).?, " + "),
+            .alloc => try genAlloc(o, inst.castTag(.alloc).?),
+            .arg => genArg(o),
+            .assembly => try genAsm(o, inst.castTag(.assembly).?),
+            .block => try genBlock(o, inst.castTag(.block).?),
+            .bitcast => try genBitcast(o, inst.castTag(.bitcast).?),
+            .breakpoint => try genBreakpoint(o, inst.castTag(.breakpoint).?),
+            .call => try genCall(o, inst.castTag(.call).?),
+            .cmp_eq => try genBinOp(o, inst.castTag(.cmp_eq).?, " == "),
+            .cmp_gt => try genBinOp(o, inst.castTag(.cmp_gt).?, " > "),
+            .cmp_gte => try genBinOp(o, inst.castTag(.cmp_gte).?, " >= "),
+            .cmp_lt => try genBinOp(o, inst.castTag(.cmp_lt).?, " < "),
+            .cmp_lte => try genBinOp(o, inst.castTag(.cmp_lte).?, " <= "),
+            .cmp_neq => try genBinOp(o, inst.castTag(.cmp_neq).?, " != "),
+            .dbg_stmt => try genDbgStmt(o, inst.castTag(.dbg_stmt).?),
+            .intcast => try genIntCast(o, inst.castTag(.intcast).?),
+            .load => try genLoad(o, inst.castTag(.load).?),
+            .ret => try genRet(o, inst.castTag(.ret).?),
+            .retvoid => try genRetVoid(o),
+            .store => try genStore(o, inst.castTag(.store).?),
+            .sub => try genBinOp(o, inst.castTag(.sub).?, " - "),
+            .unreach => try genUnreach(o, inst.castTag(.unreach).?),
+            .loop => try genLoop(o, inst.castTag(.loop).?),
+            .condbr => try genCondBr(o, inst.castTag(.condbr).?),
+            .br => try genBr(o, inst.castTag(.br).?),
+            .br_void => try genBrVoid(o, inst.castTag(.br_void).?.block),
+            .switchbr => try genSwitchBr(o, inst.castTag(.switchbr).?),
+            // bool_and and bool_or are non-short-circuit operations
+            .bool_and => try genBinOp(o, inst.castTag(.bool_and).?, " & "),
+            .bool_or => try genBinOp(o, inst.castTag(.bool_or).?, " | "),
+            .bit_and => try genBinOp(o, inst.castTag(.bit_and).?, " & "),
+            .bit_or => try genBinOp(o, inst.castTag(.bit_or).?, " | "),
+            .xor => try genBinOp(o, inst.castTag(.xor).?, " ^ "),
+            .not => try genUnOp(o, inst.castTag(.not).?, "!"),
+            else => |e| return o.dg.fail(o.dg.decl.src(), "TODO: C backend: implement codegen for {}", .{e}),
+        };
+        switch (result_value) {
+            .none => {},
+            else => try o.value_map.putNoClobber(inst, result_value),
         }
     }
 
-    try writer.writeAll("}\n\n");
+    o.indent_writer.popIndent();
+    try writer.writeAll("}");
+}
+
+fn genAlloc(o: *Object, alloc: *Inst.NoOp) !CValue {
+    const writer = o.writer();
+
+    // First line: the variable used as data storage.
+    const elem_type = alloc.base.ty.elemType();
+    const mutability: Mutability = if (alloc.base.ty.isConstPtr()) .Const else .Mut;
+    const local = try o.allocLocal(elem_type, mutability);
+    try writer.writeAll(";\n");
+
+    return CValue{ .local_ref = local.local };
+}
+
+fn genArg(o: *Object) CValue {
+    const i = o.next_arg_index;
+    o.next_arg_index += 1;
+    return .{ .arg = i };
 }
 
-fn genArg(ctx: *Context) !?[]u8 {
-    const name = try std.fmt.allocPrint(&ctx.arena.allocator, "arg{}", .{ctx.argdex});
-    ctx.argdex += 1;
-    return name;
+fn genRetVoid(o: *Object) !CValue {
+    try o.writer().print("return;\n", .{});
+    return CValue.none;
 }
 
-fn genRetVoid(ctx: *Context) !?[]u8 {
-    try ctx.file.main.writer().print(indentation ++ "return;\n", .{});
-    return null;
+fn genLoad(o: *Object, inst: *Inst.UnOp) !CValue {
+    const operand = try o.resolveInst(inst.operand);
+    const writer = o.writer();
+    const local = try o.allocLocal(inst.base.ty, .Const);
+    switch (operand) {
+        .local_ref => |i| {
+            const wrapped: CValue = .{ .local = i };
+            try writer.writeAll(" = ");
+            try o.writeCValue(writer, wrapped);
+            try writer.writeAll(";\n");
+        },
+        else => {
+            try writer.writeAll(" = *");
+            try o.writeCValue(writer, operand);
+            try writer.writeAll(";\n");
+        },
+    }
+    return local;
 }
 
-fn genRet(ctx: *Context, inst: *Inst.UnOp) !?[]u8 {
-    return ctx.file.fail(ctx.decl.src(), "TODO return", .{});
+fn genRet(o: *Object, inst: *Inst.UnOp) !CValue {
+    const operand = try o.resolveInst(inst.operand);
+    const writer = o.writer();
+    try writer.writeAll("return ");
+    try o.writeCValue(writer, operand);
+    try writer.writeAll(";\n");
+    return CValue.none;
 }
 
-fn genIntCast(ctx: *Context, inst: *Inst.UnOp) !?[]u8 {
+fn genIntCast(o: *Object, inst: *Inst.UnOp) !CValue {
     if (inst.base.isUnused())
-        return null;
-    const op = inst.operand;
-    const writer = ctx.file.main.writer();
-    const name = try ctx.name();
-    const from = try ctx.resolveInst(inst.operand);
-    try writer.writeAll(indentation ++ "const ");
-    try renderType(ctx, writer, inst.base.ty);
-    try writer.print(" {} = (", .{name});
-    try renderType(ctx, writer, inst.base.ty);
-    try writer.print("){};\n", .{from});
-    return name;
+        return CValue.none;
+
+    const from = try o.resolveInst(inst.operand);
+
+    const writer = o.writer();
+    const local = try o.allocLocal(inst.base.ty, .Const);
+    try writer.writeAll(" = (");
+    try o.dg.renderType(writer, inst.base.ty);
+    try writer.writeAll(")");
+    try o.writeCValue(writer, from);
+    try writer.writeAll(";\n");
+    return local;
 }
 
-fn genBinOp(ctx: *Context, inst: *Inst.BinOp, comptime operator: []const u8) !?[]u8 {
+fn genStore(o: *Object, inst: *Inst.BinOp) !CValue {
+    // *a = b;
+    const dest_ptr = try o.resolveInst(inst.lhs);
+    const src_val = try o.resolveInst(inst.rhs);
+
+    const writer = o.writer();
+    switch (dest_ptr) {
+        .local_ref => |i| {
+            const dest: CValue = .{ .local = i };
+            try o.writeCValue(writer, dest);
+            try writer.writeAll(" = ");
+            try o.writeCValue(writer, src_val);
+            try writer.writeAll(";\n");
+        },
+        else => {
+            try writer.writeAll("*");
+            try o.writeCValue(writer, dest_ptr);
+            try writer.writeAll(" = ");
+            try o.writeCValue(writer, src_val);
+            try writer.writeAll(";\n");
+        },
+    }
+    return CValue.none;
+}
+
+fn genBinOp(o: *Object, inst: *Inst.BinOp, operator: []const u8) !CValue {
     if (inst.base.isUnused())
-        return null;
-    const lhs = ctx.resolveInst(inst.lhs);
-    const rhs = ctx.resolveInst(inst.rhs);
-    const writer = ctx.file.main.writer();
-    const name = try ctx.name();
-    try writer.writeAll(indentation ++ "const ");
-    try renderType(ctx, writer, inst.base.ty);
-    try writer.print(" {} = {} " ++ operator ++ " {};\n", .{ name, lhs, rhs });
-    return name;
+        return CValue.none;
+
+    const lhs = try o.resolveInst(inst.lhs);
+    const rhs = try o.resolveInst(inst.rhs);
+
+    const writer = o.writer();
+    const local = try o.allocLocal(inst.base.ty, .Const);
+
+    try writer.writeAll(" = ");
+    try o.writeCValue(writer, lhs);
+    try writer.writeAll(operator);
+    try o.writeCValue(writer, rhs);
+    try writer.writeAll(";\n");
+
+    return local;
 }
 
-fn genCall(ctx: *Context, inst: *Inst.Call) !?[]u8 {
-    const writer = ctx.file.main.writer();
-    const header = ctx.file.header.writer();
-    try writer.writeAll(indentation);
+fn genUnOp(o: *Object, inst: *Inst.UnOp, operator: []const u8) !CValue {
+    if (inst.base.isUnused())
+        return CValue.none;
+
+    const operand = try o.resolveInst(inst.operand);
+
+    const writer = o.writer();
+    const local = try o.allocLocal(inst.base.ty, .Const);
+
+    try writer.print(" = {s}", .{operator});
+    try o.writeCValue(writer, operand);
+    try writer.writeAll(";\n");
+
+    return local;
+}
+
+fn genCall(o: *Object, inst: *Inst.Call) !CValue {
     if (inst.func.castTag(.constant)) |func_inst| {
-        if (func_inst.val.cast(Value.Payload.Function)) |func_val| {
-            const target = func_val.func.owner_decl;
-            const target_ty = target.typed_value.most_recent.typed_value.ty;
-            const ret_ty = target_ty.fnReturnType().tag();
-            if (target_ty.fnReturnType().hasCodeGenBits() and inst.base.isUnused()) {
+        const fn_decl = if (func_inst.val.castTag(.extern_fn)) |extern_fn|
+            extern_fn.data
+        else if (func_inst.val.castTag(.function)) |func_payload|
+            func_payload.data.owner_decl
+        else
+            unreachable;
+
+        const fn_ty = fn_decl.typed_value.most_recent.typed_value.ty;
+        const ret_ty = fn_ty.fnReturnType();
+        const unused_result = inst.base.isUnused();
+        var result_local: CValue = .none;
+
+        const writer = o.writer();
+        if (unused_result) {
+            if (ret_ty.hasCodeGenBits()) {
                 try writer.print("(void)", .{});
             }
-            const tname = mem.spanZ(target.name);
-            if (ctx.file.called.get(tname) == null) {
-                try ctx.file.called.put(tname, void{});
-                try renderFunctionSignature(ctx, header, target);
-                try header.writeAll(";\n");
-            }
-            try writer.print("{}(", .{tname});
-            if (inst.args.len != 0) {
-                for (inst.args) |arg, i| {
-                    if (i > 0) {
-                        try writer.writeAll(", ");
-                    }
-                    if (arg.cast(Inst.Constant)) |con| {
-                        try renderValue(ctx, writer, arg.ty, con.val);
-                    } else {
-                        const val = try ctx.resolveInst(arg);
-                        try writer.print("{}", .{val});
-                    }
+        } else {
+            result_local = try o.allocLocal(ret_ty, .Const);
+            try writer.writeAll(" = ");
+        }
+        const fn_name = mem.spanZ(fn_decl.name);
+        try writer.print("{s}(", .{fn_name});
+        if (inst.args.len != 0) {
+            for (inst.args) |arg, i| {
+                if (i > 0) {
+                    try writer.writeAll(", ");
+                }
+                if (arg.value()) |val| {
+                    try o.dg.renderValue(writer, arg.ty, val);
+                } else {
+                    const val = try o.resolveInst(arg);
+                    try o.writeCValue(writer, val);
                 }
             }
-            try writer.writeAll(");\n");
-        } else {
-            return ctx.file.fail(ctx.decl.src(), "TODO non-function call target?", .{});
         }
+        try writer.writeAll(");\n");
+        return result_local;
     } else {
-        return ctx.file.fail(ctx.decl.src(), "TODO non-constant call inst?", .{});
+        return o.dg.fail(o.dg.decl.src(), "TODO: C backend: implement function pointers", .{});
     }
-    return null;
 }
 
-fn genDbgStmt(ctx: *Context, inst: *Inst.NoOp) !?[]u8 {
+fn genDbgStmt(o: *Object, inst: *Inst.NoOp) !CValue {
     // TODO emit #line directive here with line number and filename
-    return null;
+    return CValue.none;
+}
+
+fn genBlock(o: *Object, inst: *Inst.Block) !CValue {
+    const block_id: usize = o.next_block_index;
+    o.next_block_index += 1;
+    const writer = o.writer();
+
+    // store the block id in relocs.capacity as it is not  used for anything else in the C backend.
+    inst.codegen.relocs.capacity = block_id;
+    const result = if (inst.base.ty.tag() != .void and !inst.base.isUnused()) blk: {
+        // allocate a location for the result
+        const local = try o.allocLocal(inst.base.ty, .Mut);
+        try writer.writeAll(";\n");
+        break :blk local;
+    } else CValue{ .none = {} };
+
+    inst.codegen.mcv = @bitCast(@import("../codegen.zig").AnyMCValue, result);
+    try genBody(o, inst.body);
+    try o.indent_writer.insertNewline();
+    // label must be followed by an expression, add an empty one.
+    try writer.print("zig_block_{d}:;\n", .{block_id});
+    return result;
+}
+
+fn genBr(o: *Object, inst: *Inst.Br) !CValue {
+    const result = @bitCast(CValue, inst.block.codegen.mcv);
+    const writer = o.writer();
+
+    // If result is .none then the value of the block is unused.
+    if (inst.operand.ty.tag() != .void and result != .none) {
+        const operand = try o.resolveInst(inst.operand);
+        try o.writeCValue(writer, result);
+        try writer.writeAll(" = ");
+        try o.writeCValue(writer, operand);
+        try writer.writeAll(";\n");
+    }
+
+    return genBrVoid(o, inst.block);
 }
 
-fn genBreak(ctx: *Context, inst: *Inst.NoOp) !?[]u8 {
-    // TODO ??
-    return null;
+fn genBrVoid(o: *Object, block: *Inst.Block) !CValue {
+    try o.writer().print("goto zig_block_{d};\n", .{block.codegen.relocs.capacity});
+    return CValue.none;
 }
 
-fn genUnreach(ctx: *Context, inst: *Inst.NoOp) !?[]u8 {
-    try ctx.file.main.writer().writeAll(indentation ++ "zig_unreachable();\n");
-    return null;
+fn genBitcast(o: *Object, inst: *Inst.UnOp) !CValue {
+    const operand = try o.resolveInst(inst.operand);
+
+    const writer = o.writer();
+    if (inst.base.ty.zigTypeTag() == .Pointer and inst.operand.ty.zigTypeTag() == .Pointer) {
+        const local = try o.allocLocal(inst.base.ty, .Const);
+        try writer.writeAll(" = (");
+        try o.dg.renderType(writer, inst.base.ty);
+
+        try writer.writeAll(")");
+        try o.writeCValue(writer, operand);
+        try writer.writeAll(";\n");
+        return local;
+    }
+
+    const local = try o.allocLocal(inst.base.ty, .Mut);
+    try writer.writeAll(";\n");
+
+    try writer.writeAll("memcpy(&");
+    try o.writeCValue(writer, local);
+    try writer.writeAll(", &");
+    try o.writeCValue(writer, operand);
+    try writer.writeAll(", sizeof ");
+    try o.writeCValue(writer, local);
+    try writer.writeAll(");\n");
+
+    return local;
 }
 
-fn genAsm(ctx: *Context, as: *Inst.Assembly) !?[]u8 {
-    const writer = ctx.file.main.writer();
-    try writer.writeAll(indentation);
+fn genBreakpoint(o: *Object, inst: *Inst.NoOp) !CValue {
+    try o.writer().writeAll("zig_breakpoint();\n");
+    return CValue.none;
+}
+
+fn genUnreach(o: *Object, inst: *Inst.NoOp) !CValue {
+    try o.writer().writeAll("zig_unreachable();\n");
+    return CValue.none;
+}
+
+fn genLoop(o: *Object, inst: *Inst.Loop) !CValue {
+    try o.writer().writeAll("while (true) ");
+    try genBody(o, inst.body);
+    try o.indent_writer.insertNewline();
+    return CValue.none;
+}
+
+fn genCondBr(o: *Object, inst: *Inst.CondBr) !CValue {
+    const cond = try o.resolveInst(inst.condition);
+    const writer = o.writer();
+
+    try writer.writeAll("if (");
+    try o.writeCValue(writer, cond);
+    try writer.writeAll(") ");
+    try genBody(o, inst.then_body);
+    try writer.writeAll(" else ");
+    try genBody(o, inst.else_body);
+    try o.indent_writer.insertNewline();
+
+    return CValue.none;
+}
+
+fn genSwitchBr(o: *Object, inst: *Inst.SwitchBr) !CValue {
+    const target = try o.resolveInst(inst.target);
+    const writer = o.writer();
+
+    try writer.writeAll("switch (");
+    try o.writeCValue(writer, target);
+    try writer.writeAll(") {\n");
+    o.indent_writer.pushIndent();
+
+    for (inst.cases) |case| {
+        try writer.writeAll("case ");
+        try o.dg.renderValue(writer, inst.target.ty, case.item);
+        try writer.writeAll(": ");
+        // the case body must be noreturn so we don't need to insert a break
+        try genBody(o, case.body);
+        try o.indent_writer.insertNewline();
+    }
+
+    try writer.writeAll("default: ");
+    try genBody(o, inst.else_body);
+    try o.indent_writer.insertNewline();
+
+    o.indent_writer.popIndent();
+    try writer.writeAll("}\n");
+    return CValue.none;
+}
+
+fn genAsm(o: *Object, as: *Inst.Assembly) !CValue {
+    if (as.base.isUnused() and !as.is_volatile)
+        return CValue.none;
+
+    const writer = o.writer();
     for (as.inputs) |i, index| {
         if (i[0] == '{' and i[i.len - 1] == '}') {
             const reg = i[1 .. i.len - 1];
             const arg = as.args[index];
+            const arg_c_value = try o.resolveInst(arg);
             try writer.writeAll("register ");
-            try renderType(ctx, writer, arg.ty);
-            try writer.print(" {}_constant __asm__(\"{}\") = ", .{ reg, reg });
-            // TODO merge constant handling into inst_map as well
-            if (arg.castTag(.constant)) |c| {
-                try renderValue(ctx, writer, arg.ty, c.val);
-                try writer.writeAll(";\n    ");
-            } else {
-                const gop = try ctx.inst_map.getOrPut(arg);
-                if (!gop.found_existing) {
-                    return ctx.file.fail(ctx.decl.src(), "Internal error in C backend: asm argument not found in inst_map", .{});
-                }
-                try writer.print("{};\n    ", .{gop.entry.value});
-            }
+            try o.dg.renderType(writer, arg.ty);
+
+            try writer.print(" {s}_constant __asm__(\"{s}\") = ", .{ reg, reg });
+            try o.writeCValue(writer, arg_c_value);
+            try writer.writeAll(";\n");
         } else {
-            return ctx.file.fail(ctx.decl.src(), "TODO non-explicit inline asm regs", .{});
+            return o.dg.fail(o.dg.decl.src(), "TODO non-explicit inline asm regs", .{});
         }
     }
-    try writer.print("__asm {} (\"{}\"", .{ if (as.is_volatile) @as([]const u8, "volatile") else "", as.asm_source });
-    if (as.output) |o| {
-        return ctx.file.fail(ctx.decl.src(), "TODO inline asm output", .{});
+    const volatile_string: []const u8 = if (as.is_volatile) "volatile " else "";
+    try writer.print("__asm {s}(\"{s}\"", .{ volatile_string, as.asm_source });
+    if (as.output) |_| {
+        return o.dg.fail(o.dg.decl.src(), "TODO inline asm output", .{});
     }
     if (as.inputs.len > 0) {
         if (as.output == null) {
@@ -320,7 +782,7 @@ fn genAsm(ctx: *Context, as: *Inst.Assembly) !?[]u8 {
                 if (index > 0) {
                     try writer.writeAll(", ");
                 }
-                try writer.print("\"\"({}_constant)", .{reg});
+                try writer.print("\"r\"({s}_constant)", .{reg});
             } else {
                 // This is blocked by the earlier test
                 unreachable;
@@ -328,5 +790,62 @@ fn genAsm(ctx: *Context, as: *Inst.Assembly) !?[]u8 {
         }
     }
     try writer.writeAll(");\n");
-    return null;
+
+    if (as.base.isUnused())
+        return CValue.none;
+
+    return o.dg.fail(o.dg.decl.src(), "TODO: C backend: inline asm expression result used", .{});
+}
+
+fn IndentWriter(comptime UnderlyingWriter: type) type {
+    return struct {
+        const Self = @This();
+        pub const Error = UnderlyingWriter.Error;
+        pub const Writer = std.io.Writer(*Self, Error, write);
+
+        pub const indent_delta = 4;
+
+        underlying_writer: UnderlyingWriter,
+        indent_count: usize = 0,
+        current_line_empty: bool = true,
+
+        pub fn writer(self: *Self) Writer {
+            return .{ .context = self };
+        }
+
+        pub fn write(self: *Self, bytes: []const u8) Error!usize {
+            if (bytes.len == 0) return @as(usize, 0);
+
+            const current_indent = self.indent_count * Self.indent_delta;
+            if (self.current_line_empty and current_indent > 0) {
+                try self.underlying_writer.writeByteNTimes(' ', current_indent);
+            }
+            self.current_line_empty = false;
+
+            return self.writeNoIndent(bytes);
+        }
+
+        pub fn insertNewline(self: *Self) Error!void {
+            _ = try self.writeNoIndent("\n");
+        }
+
+        pub fn pushIndent(self: *Self) void {
+            self.indent_count += 1;
+        }
+
+        pub fn popIndent(self: *Self) void {
+            assert(self.indent_count != 0);
+            self.indent_count -= 1;
+        }
+
+        fn writeNoIndent(self: *Self, bytes: []const u8) Error!usize {
+            if (bytes.len == 0) return @as(usize, 0);
+
+            try self.underlying_writer.writeAll(bytes);
+            if (bytes[bytes.len - 1] == '\n') {
+                self.current_line_empty = true;
+            }
+            return bytes.len;
+        }
+    };
 }