From 4481d48709ecc2eda7f6eaba86e9b94511d418c4 Mon Sep 17 00:00:00 2001
From: David Mak <david.18.19.21@gmail.com>
Date: Tue, 5 Sep 2023 18:05:05 +0800
Subject: [PATCH] core: Use C-style for loop logic for iterables

Index increment is now performed at the end of the loop body.
---
 nac3core/src/codegen/stmt.rs             | 18 +++++++++---------
 nac3standalone/demo/src/loop_iterable.py | 17 +++++++++++++++++
 2 files changed, 26 insertions(+), 9 deletions(-)
 create mode 100644 nac3standalone/demo/src/loop_iterable.py

diff --git a/nac3core/src/codegen/stmt.rs b/nac3core/src/codegen/stmt.rs
index f1edf77d..b310097d 100644
--- a/nac3core/src/codegen/stmt.rs
+++ b/nac3core/src/codegen/stmt.rs
@@ -321,9 +321,8 @@ pub fn gen_for<'ctx, 'a, G: CodeGenerator>(
         } else {
             let test_bb = backedge_bb_target;
 
-            let counter = generator.gen_var_alloc(ctx, size_t.into(), Some("for.counter.addr"))?;
-            // counter = -1
-            ctx.builder.build_store(counter, size_t.const_int(u64::max_value(), true));
+            let index_addr = generator.gen_var_alloc(ctx, size_t.into(), Some("for.index.addr"))?;
+            ctx.builder.build_store(index_addr, size_t.const_zero());
             let len = ctx
                 .build_gep_and_load(
                     iter_val.into_pointer_value(),
@@ -333,20 +332,21 @@ pub fn gen_for<'ctx, 'a, G: CodeGenerator>(
             ctx.builder.build_unconditional_branch(test_bb);
 
             ctx.builder.position_at_end(test_bb);
-            let tmp = ctx.builder.build_load(counter, "i").into_int_value();
-            let tmp = ctx.builder.build_int_add(tmp, size_t.const_int(1, false), "inc");
-            ctx.builder.build_store(counter, tmp);
-            let cmp = ctx.builder.build_int_compare(IntPredicate::SLT, tmp, len, "cmp");
+            let index = ctx.builder.build_load(index_addr, "for.index").into_int_value();
+            let cmp = ctx.builder.build_int_compare(IntPredicate::SLT, index, len, "cond");
             ctx.builder.build_conditional_branch(cmp, body_bb, orelse_bb);
 
             ctx.builder.position_at_end(body_bb);
             let arr_ptr = ctx
                 .build_gep_and_load(iter_val.into_pointer_value(), &[zero, zero])
                 .into_pointer_value();
-            let val = ctx.build_gep_and_load(arr_ptr, &[tmp]);
+            let val = ctx.build_gep_and_load(arr_ptr, &[index]);
             generator.gen_assign(ctx, target, val.into())?;
-
             gen_block(generator, ctx, body.iter())?;
+
+            let index = ctx.builder.build_load(index_addr, "for.index").into_int_value();
+            let inc = ctx.builder.build_int_add(index, size_t.const_int(1, true), "");
+            ctx.builder.build_store(index_addr, inc);
         }
 
         for (k, (_, _, counter)) in var_assignment.iter() {
diff --git a/nac3standalone/demo/src/loop_iterable.py b/nac3standalone/demo/src/loop_iterable.py
new file mode 100644
index 00000000..d97ab305
--- /dev/null
+++ b/nac3standalone/demo/src/loop_iterable.py
@@ -0,0 +1,17 @@
+# For Loop using a list as its iterable
+
+@extern
+def output_int32(x: int32):
+    ...
+
+def run() -> int32:
+    l = [0, 1, 2, 3, 4]
+
+    # i: int32  # declaration-without-initializer not yet supported
+    i = 0       # i must be declared before the loop; this is not necessary in Python
+    for i in l:
+        output_int32(i)
+        i = 0
+        output_int32(i)
+    output_int32(i)
+    return 0