core: Fix IR generation of for loop containing break/continue

Fix cases where the body BB would have two terminators because of a
preceding continue/break statement already emitting a terminator.

nac3core/src/codegen/stmt.rs

@@ -253,21 +253,22 @@ pub fn gen_for<'ctx, 'a, G: CodeGenerator>(
         let body_bb = ctx.ctx.append_basic_block(current, "for.body");
         let cont_bb = ctx.ctx.append_basic_block(current, "for.end");
         // if there is no orelse, we just go to cont_bb
-        let orelse_bb =
+        let orelse_bb = if orelse.is_empty() {
-            if orelse.is_empty() { cont_bb } else { ctx.ctx.append_basic_block(current, "for.orelse") };
+            cont_bb
+        } else {
+            ctx.ctx.append_basic_block(current, "for.orelse")
+        };
 
         // Whether the iterable is a range() expression
         let is_iterable_range_expr = ctx.unifier.unioned(iter.custom.unwrap(), ctx.primitives.range);
 
-        // The target BB of the loop backedge
+        // The BB containing the increment expression
-        let backedge_bb_target = if is_iterable_range_expr {
+        let incr_bb = ctx.ctx.append_basic_block(current, "for.incr");
-            body_bb
+        // The BB containing the loop condition check
-        } else {
+        let cond_bb = ctx.ctx.append_basic_block(current, "for.cond");
-            ctx.ctx.append_basic_block(current, "for.cond")
-        };
 
         // store loop bb information and restore it later
-        let loop_bb = ctx.loop_target.replace((backedge_bb_target, cont_bb));
+        let loop_bb = ctx.loop_target.replace((incr_bb, cont_bb));
 
         let iter_val = generator.gen_expr(ctx, iter)?.unwrap().to_basic_value_enum(
             ctx,
@@ -294,35 +295,35 @@ pub fn gen_for<'ctx, 'a, G: CodeGenerator>(
                 [None, None, None],
                 ctx.current_loc
             );
+            ctx.builder.build_unconditional_branch(cond_bb);
 
+            {
+                ctx.builder.position_at_end(cond_bb);
                 ctx.builder.build_conditional_branch(
-                gen_in_range_check(ctx, start, stop, step),
+                    gen_in_range_check(
+                        ctx,
+                        ctx.builder.build_load(i, "").into_int_value(),
+                        stop,
+                        step
+                    ),
                     body_bb,
                     orelse_bb,
                 );
+            }
+
+            ctx.builder.position_at_end(incr_bb);
+            let next_i = ctx.builder.build_int_add(
+                ctx.builder.build_load(i, "").into_int_value(),
+                step,
+                "inc",
+            );
+            ctx.builder.build_store(i, next_i);
+            ctx.builder.build_unconditional_branch(cond_bb);
 
             ctx.builder.position_at_end(body_bb);
             ctx.builder.build_store(target_i, ctx.builder.build_load(i, "").into_int_value());
             gen_block(generator, ctx, body.iter())?;
-
-            // Test if next element is still in range
-            let next_i = ctx.builder.build_int_add(
-                ctx.builder.build_load(i, "").into_int_value(),
-                step,
-                "next_i",
-            );
-            let cond_cont_bb = ctx.ctx.append_basic_block(current, "for.cond.cont");
-            ctx.builder.build_conditional_branch(
-                gen_in_range_check(ctx, next_i, stop, step),
-                cond_cont_bb,
-                orelse_bb,
-            );
-
-            ctx.builder.position_at_end(cond_cont_bb);
-            ctx.builder.build_store(i, next_i);
         } else {
-            let test_bb = backedge_bb_target;
-
             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
@@ -332,24 +333,27 @@ pub fn gen_for<'ctx, 'a, G: CodeGenerator>(
                     Some("len")
                 )
                 .into_int_value();
-            ctx.builder.build_unconditional_branch(test_bb);
+            ctx.builder.build_unconditional_branch(cond_bb);
 
-            ctx.builder.position_at_end(test_bb);
+            ctx.builder.position_at_end(cond_bb);
             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(incr_bb);
+            let index = ctx.builder.build_load(index_addr, "").into_int_value();
+            let inc = ctx.builder.build_int_add(index, size_t.const_int(1, true), "inc");
+            ctx.builder.build_store(index_addr, inc);
+            ctx.builder.build_unconditional_branch(cond_bb);
+
             ctx.builder.position_at_end(body_bb);
             let arr_ptr = ctx
                 .build_gep_and_load(iter_val.into_pointer_value(), &[zero, zero], Some("arr.addr"))
                 .into_pointer_value();
+            let index = ctx.builder.build_load(index_addr, "for.index").into_int_value();
             let val = ctx.build_gep_and_load(arr_ptr, &[index], Some("val"));
             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() {
@@ -360,7 +364,7 @@ pub fn gen_for<'ctx, 'a, G: CodeGenerator>(
         }
 
         if !ctx.is_terminated() {
-            ctx.builder.build_unconditional_branch(backedge_bb_target);
+            ctx.builder.build_unconditional_branch(incr_bb);
         }
 
         if !orelse.is_empty() {

nac3standalone/demo/src/loop_cont_break.py

@@ -0,0 +1,21 @@
+@extern
+def output_int32(x: int32):
+    ...
+
+def run() -> int32:
+    for i in range(4):
+        output_int32(i)
+        if i < 2:
+            continue
+        else:
+            break
+
+    n = [0, 1, 2, 3]
+    for i in n:
+        output_int32(i)
+        if i < 2:
+            continue
+        else:
+            break
+
+    return 0