Do not initialise zero-sized types (#5741)

Fixes #5692

Author: vaivaswatha

sway-core/src/asm_generation/fuel/functions.rs

@@ -851,6 +851,10 @@ impl<'ir, 'eng> FuelAsmBuilder<'ir, 'eng> {
             data_id,
         } in init_mut_vars
         {
+            if var_size.in_bytes() == 0 {
+                // Don't bother initializing zero-sized types.
+                continue;
+            }
             // Load our initialiser from the data section.
             self.cur_bytecode.push(Op {
                 opcode: Either::Left(VirtualOp::LoadDataId(

test/src/e2e_vm_tests/test_programs/should_pass/language/mut_ref_empty_type/Forc.lock

@@ -0,0 +1,13 @@
+[[package]]
+name = "core"
+source = "path+from-root-3299F53BAA3C44EE"
+
+[[package]]
+name = "mut_ref_empty_type"
+source = "member"
+dependencies = ["std"]
+
+[[package]]
+name = "std"
+source = "path+from-root-3299F53BAA3C44EE"
+dependencies = ["core"]

test/src/e2e_vm_tests/test_programs/should_pass/language/mut_ref_empty_type/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+authors = ["Fuel Labs <contact@fuel.sh>"]
+entry = "main.sw"
+license = "Apache-2.0"
+name = "mut_ref_empty_type"
+
+[dependencies]
+std = { path = "../../../../../../../sway-lib-std" }

test/src/e2e_vm_tests/test_programs/should_pass/language/mut_ref_empty_type/json_abi_oracle.json

@@ -0,0 +1,25 @@
+{
+  "configurables": [],
+  "functions": [
+    {
+      "attributes": null,
+      "inputs": [],
+      "name": "main",
+      "output": {
+        "name": "",
+        "type": 0,
+        "typeArguments": null
+      }
+    }
+  ],
+  "loggedTypes": [],
+  "messagesTypes": [],
+  "types": [
+    {
+      "components": null,
+      "type": "u64",
+      "typeId": 0,
+      "typeParameters": null
+    }
+  ]
+}

test/src/e2e_vm_tests/test_programs/should_pass/language/mut_ref_empty_type/src/main.sw

@@ -0,0 +1,64 @@
+script;
+
+pub trait New {
+    fn new() -> Self;
+}
+
+impl New for [u64;0] {
+    fn new() -> Self {
+        []
+    }
+}
+
+impl Eq for [u64;0] {
+     fn eq(self, other: Self) -> bool {
+        true
+     }
+}
+
+struct EmptyStruct { }
+
+impl New for EmptyStruct {
+    fn new() -> Self {
+        EmptyStruct { }
+    }
+}
+
+impl Eq for EmptyStruct {
+     fn eq(self, other: Self) -> bool {
+        true
+     }
+}
+
+#[inline(always)]
+fn reference_zero_sized_local_var_and_value<T>()
+    where T: New + Eq
+{
+    assert(__size_of::<T>() == 0);
+
+    let mut x1 = T::new();
+    let x2 = T::new();
+
+    let x_ptr1 = asm(r: &x1) { r: raw_ptr };
+    let res1 = x_ptr1.read::<T>();
+
+    let x_ptr2 = __addr_of(x2);
+    let res2 = x_ptr2.read::<T>();
+    assert(res1 == res2);
+}
+
+#[inline(never)]
+fn reference_zero_sized_local_var_and_value_not_inlined<T>()
+    where T: New + Eq
+{
+    reference_zero_sized_local_var_and_value::<T>()
+}
+
+fn main() -> u64 {
+    reference_zero_sized_local_var_and_value_not_inlined::<EmptyStruct>();
+    reference_zero_sized_local_var_and_value_not_inlined::<[u64;0]>();
+    reference_zero_sized_local_var_and_value::<EmptyStruct>();
+    reference_zero_sized_local_var_and_value::<[u64;0]>();
+
+    42
+}

test/src/e2e_vm_tests/test_programs/should_pass/language/mut_ref_empty_type/test.toml

@@ -0,0 +1,4 @@
+category = "run"
+expected_result = { action = "return", value = 42 }
+validate_abi = true
+expected_warnings = 2