Compiler: force zero initialization of local variables

* make all local variables zero-initialized except if tagged as `@(noinit)`
* update tests

Author: chqrlie

ast/ast_evaluator.c2

@@ -284,17 +284,17 @@ fn Value Evaluator.eval_call(Evaluator* caller, const CallExpr* c) {
 
     // Create a new stack frame and link it to the caller's
     // TODO: handle Stack frames as separate allocated objects
-    Evaluator eval;
-
-    if (num_args > elemsof(eval.args)) {
-        return Value.error("too many arguments in pure function evaluation");
-    }
+    Evaluator eval /*@(noinit)*/;
     eval.prev = caller;
     eval.fd = fd;
     eval.num_args = num_args;
     eval.depth = caller.depth + 1;
     eval.complexity = caller.complexity + 1;
 
+    if (num_args > elemsof(eval.args)) {
+        return Value.error("too many arguments in pure function evaluation");
+    }
+
     //VarDecl** params = fd.getParams();
 
     for (u32 i = 0; i < num_args; i++) {

ast/value.c2

@@ -804,7 +804,7 @@ fn f64 fabs(f64 d) {
 // string and trying to avoid using exponential notation
 // TODO: should be in the C2 library as a type function f64.str()
 public fn char *ftoa(char *dest, usize size, f64 d) {
-    char[32] buf;
+    char[32] buf /*@(noinit)*/;
     usize pos = 0;
 
     if (size < 2) {

ast/var_decl.c2

@@ -57,6 +57,7 @@ type VarDeclBits struct {
     u32 addr_used : 1;
     AutoAttr auto_attr : 2;  // for parameters only
     FormatAttr format_attr : 2; // for parameters only
+    u32 attr_noinit : 1;
 }
 
 public type BitFieldLayout struct {
@@ -303,6 +304,14 @@ public fn bool VarDecl.hasInitCall(const VarDecl* d) {
     return d.base.varDeclBits.has_init_call;
 }
 
+public fn void VarDecl.setAttrNoInit(VarDecl* d) {
+    d.base.varDeclBits.attr_noinit = 1;
+}
+
+public fn bool VarDecl.hasAttrNoInit(const VarDecl* d) {
+    return d.base.varDeclBits.attr_noinit;
+}
+
 public fn void VarDecl.setAttrWeak(VarDecl* d) {
     d.base.varDeclBits.attr_weak = 1;
 }

ast_utils/attr.c2

@@ -44,6 +44,7 @@ public type AttrKind enum u8 {
     AutoFunc,       //               Var, function param only
     Embed,          //               Var, globals only
     Deprecated,     //        Func
+    NoInit,         //               Var
 }
 
 const char*[AttrKind] attrKind_names = {
@@ -71,6 +72,7 @@ const char*[AttrKind] attrKind_names = {
     "auto_func",
     "embed",
     "deprecated",
+    "noinit",
 }
 
 public type AttrValueKind enum u8 {
@@ -148,6 +150,7 @@ const AttrReq[AttrKind] Required_arg = {
     [AutoFunc]     = NoArg,
     [Embed]        = String,
     [Deprecated]   = String,
+    [NoInit]       = NoArg,
 }
 
 public type AttrReq enum u8 {

ast_utils/string_buffer.c2

@@ -169,7 +169,7 @@ public fn void Buf.stripTrailingSpaces(Buf* buf) {
 }
 
 public fn void Buf.print(Buf* buf, const char* format @(printf_format), ...) {
-    char[4096] tmp;
+    char[4096] tmp /*@(noinit)*/;
     // NOTE: no growing
     va_list args;
     va_start(args, format);
@@ -180,7 +180,7 @@ public fn void Buf.print(Buf* buf, const char* format @(printf_format), ...) {
 }
 
 public fn void Buf.vprintf(Buf* buf, const char* format, va_list args) {
-    char[4096] tmp;
+    char[4096] tmp /*@(noinit)*/;
     // NOTE: no growing
     i32 len = vsnprintf(tmp, elemsof(tmp), format, args);
     assert(len < elemsof(tmp));

common/ast_builder.c2

@@ -511,6 +511,9 @@ fn void Builder.actOnVarAttr(Builder* b, Decl* d, const Attr* a) {
     case Embed:
         b.storeAttr(d, a);
         break;
+    case NoInit:
+        vd.setAttrNoInit();
+        break;
     default:
         b.diags.error(a.loc, "attribute '%s' is not applicable to variables",
                       a.kind2name());

common/file/file_utils.c2

@@ -116,7 +116,7 @@ public fn const char* make_path3(char *buf, usize size, const char* dir, const c
 // returns 0 on success, errno on failure
 // create a directory path, OK if exists already
 public fn i32 create_path(const char* path) {
-    char[file_utils.Max_path] tmp;
+    char[file_utils.Max_path] tmp /*@(noinit)*/;
     char *p = tmp;
     if (!*path) return 0;
     *p++ = *path++;

generator/c/c_generator.c2

@@ -1295,8 +1295,7 @@ public fn void generate(string_pool.Pool* astPool,
         return;
     }
 
-    Generator gen;
-    gen.init(astPool, target, kind, output_dir, dir, diags, sm, build_info, mainFunc);
+    Generator gen.init(astPool, target, kind, output_dir, dir, diags, sm, build_info, mainFunc);
     gen.auxPool = auxPool;
     gen.enable_asserts = enable_asserts;
     gen.fast_build = fast_build;

generator/c/c_generator_special.c2

@@ -60,7 +60,7 @@ fn void Generator.createMakefile(Generator* gen,
     out.print("CC=%s\n", cc);
 
     out.add("CFLAGS=-Wall -Wextra -Wno-unused -Wno-switch\n");
-    out.add("CFLAGS+=-Wno-unused-parameter -Wno-missing-field-initializers -Wno-format-zero-length\n");
+    out.add("CFLAGS+=-Wno-unused-parameter -Wno-missing-field-initializers -Wno-missing-braces -Wno-format-zero-length\n");
     out.add("CFLAGS+=-pipe -std=c99 -funsigned-char\n");
     if (gen.fast_build)
         out.add("CFLAGS+=-O0 -g\n");

generator/c/c_generator_stmt.c2

@@ -40,6 +40,10 @@ fn void Generator.emitVarDecl(Generator* gen, VarDecl* vd, string_buffer.Buf* ou
             out.add(" = ");
         }
         gen.emitExpr(out, ie);
+    } else {
+        if (!vd.hasAttrNoInit()) {
+            out.add(" = { 0 }");
+        }
     }
 }