Set the type of the implicit blocks we use for a loop body in s2wasm (#810)

Loops are modeled in Binaryen IR as having a Block as a body. The block
is added to module walkers and validated like a normal block.
In s2wasm when we add the blocks, we need to make sure that the type of
the loop body matches the type of the loop itself, or we run into
issues.

3 files changed, 22 insertions, 0 deletions

diff --git a/src/s2wasm.h b/src/s2wasm.h
index 1e52cfbce..c5b502c6d 100644
--- a/src/s2wasm.h
+++ b/src/s2wasm.h
@@ -1129,6 +1129,7 @@ class S2WasmBuilder {
         curr->name = getNextLabel();
         auto implicitBlock = allocator->alloc<Block>();
         curr->body = implicitBlock;
+        implicitBlock->type = loopType;
         bstack.push_back(curr);
       } else if (match("end_loop")) {
         auto* loop = bstack.back()->cast<Loop>();
diff --git a/test/dot_s/return.s b/test/dot_s/return.s
index 5a0bded5a..9ceaabaf5 100644
--- a/test/dot_s/return.s
+++ b/test/dot_s/return.s
@@ -15,3 +15,15 @@ return_void:
 .Lfunc_end0:
 	.size	return_void, .Lfunc_end0-return_void
 
+  .type fallthrough_return_nested_loop_i32,@function
+fallthrough_return_nested_loop_i32:
+  .result   i32
+  loop      i32
+  loop      i32
+  i32.const $push0=, 1
+  return    $pop0
+  end_loop
+  end_loop
+  .endfunc
+.Lfunc_end0:
+  .size fallthrough_return_nested_loop_i32, .Lfunc_end0-fallthrough_return_nested_loop_i32
diff --git a/test/dot_s/return.wast b/test/dot_s/return.wast
index 896e99357..ee7bc2ed2 100644
--- a/test/dot_s/return.wast
+++ b/test/dot_s/return.wast
@@ -8,5 +8,14 @@
   )
   (func $return_void
   )
+  (func $fallthrough_return_nested_loop_i32 (result i32)
+    (loop $label$0 i32
+      (loop $label$1 i32
+        (return
+          (i32.const 1)
+        )
+      )
+    )
+  )
 )
 ;; METADATA: { "asmConsts": {},"staticBump": 12, "initializers": [] }