handle an unreachable block with a reachable final element in merge-blocks

Author: kripken

src/passes/MergeBlocks.cpp

@@ -188,6 +188,15 @@ static void optimizeBlock(Block* curr, Module* module) {
       }
       if (!child) continue;
       if (child->name.is()) continue; // named blocks can have breaks to them (and certainly do, if we ran RemoveUnusedNames and RemoveUnusedBrs)
+      if (child->type == unreachable) {
+        // an unreachable block can have a concrete final element (which is never reached)
+        if (!child->list.empty()) {
+          if (isConcreteWasmType(child->list.back()->type)) {
+            // just remove it
+            child->list.pop_back();
+          }
+        }
+      }
       ExpressionList merged(module->allocator);
       for (size_t j = 0; j < i; j++) {
         merged.push_back(curr->list[j]);

test/passes/remove-unused-names_merge-blocks.txt

@@ -4,6 +4,7 @@
  (type $iii (func (param i32 i32 i32)))
  (type $3 (func))
  (type $4 (func (result i32)))
+ (type $5 (func (result f64)))
  (table 1 1 anyfunc)
  (elem (i32.const 0) $call-i)
  (memory $0 256 256)
@@ -748,4 +749,8 @@
   )
   (unreachable)
  )
+ (func $concrete_finale_in_unreachable (type $5) (result f64)
+  (unreachable)
+  (f64.const -1)
+ )
 )

test/passes/remove-unused-names_merge-blocks.wast

@@ -926,4 +926,13 @@
    (unreachable)
   )
  )
+ (func $concrete_finale_in_unreachable (result f64)
+  (block $label$0 (result f64)
+   (block ;; this block is unreachable
+    (unreachable)
+    (f64.const 6.322092475576799e-96)
+   )
+   (f64.const -1)
+  )
+ )
 )