From ad91bde59722cada146f52d776f3a67952965215 Mon Sep 17 00:00:00 2001
From: Brendan Hansen <brendan.f.hansen@gmail.com>
Date: Sat, 4 Dec 2021 12:14:43 -0600
Subject: [PATCH] implicit zero-ing of stack allocated variables

---
 include/astnodes.h |  2 ++
 src/checker.c      |  7 +++++++
 src/wasm_emit.c    | 23 ++++++++++++++++++++++-
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/include/astnodes.h b/include/astnodes.h
index 3b76bd00..66deb9a8 100644
--- a/include/astnodes.h
+++ b/include/astnodes.h
@@ -260,6 +260,8 @@ typedef enum AstFlags {
     Ast_Flag_Symbol_Invisible      = BH_BIT(18),
 
     Ast_Flag_Header_Check_No_Error = BH_BIT(19),
+
+    Ast_Flag_Decl_Followed_By_Init = BH_BIT(20),
 } AstFlags;
 
 typedef enum UnaryOp {
diff --git a/src/checker.c b/src/checker.c
index 72d2350c..20cc4723 100644
--- a/src/checker.c
+++ b/src/checker.c
@@ -1911,6 +1911,13 @@ CheckStatus check_statement(AstNode** pstmt) {
 
                 YIELD(typed_stmt->token->pos, "Waiting for local variable's type.");
             }
+
+            if (typed_stmt->next != NULL && typed_stmt->next->kind == Ast_Kind_Binary_Op) {
+                AstBinaryOp *next = (AstBinaryOp *) typed_stmt->next;
+                if (next->operation == Binary_Op_Assign && next->left == typed_stmt) {
+                    typed_stmt->flags |= Ast_Flag_Decl_Followed_By_Init;
+                }
+            }
             return Check_Success;
         }
 
diff --git a/src/wasm_emit.c b/src/wasm_emit.c
index b7aea1a6..2a9f5b98 100644
--- a/src/wasm_emit.c
+++ b/src/wasm_emit.c
@@ -439,7 +439,28 @@ EMIT_FUNC(statement, AstNode* stmt) {
 }
 
 EMIT_FUNC(local_allocation, AstTyped* stmt) {
-    bh_imap_put(&mod->local_map, (u64) stmt, local_allocate(mod->local_alloc, stmt));
+    u64 local_idx = local_allocate(mod->local_alloc, stmt);
+    bh_imap_put(&mod->local_map, (u64) stmt, local_idx);
+
+    if (stmt->kind == Ast_Kind_Local && !(stmt->flags & Ast_Flag_Decl_Followed_By_Init)) {
+        bh_arr(WasmInstruction) code = *pcode;
+        if (local_is_wasm_local(stmt)) {
+            emit_zero_value(mod, &code, onyx_type_to_wasm_type(stmt->type));
+            WIL(WI_LOCAL_SET, local_idx);
+
+        } else {
+            emit_location(mod, &code, stmt);
+            WID(WI_I32_CONST, 0);
+            WID(WI_I32_CONST, type_size_of(stmt->type));
+            if (context.options->use_post_mvp_features) {
+                WID(WI_MEMORY_FILL, 0x00);
+            } else {
+                emit_intrinsic_memory_fill(mod, &code);
+            }
+        }
+
+        *pcode = code;
+    }
 
     bh_arr_push(mod->local_allocations, ((AllocatedSpace) {
         .depth = bh_arr_length(mod->structured_jump_target),
-- 
2.25.1