Return to more structured type rules for block and if (#1148)

* if a block has a concrete final element (or a break with a value), then even if it has an unreachable child, keep it with that concrete type. this means we no longe allow the silly case of a block with an unreachable in the middle and a concrete as the final element while the block is unreachable - after this change, the block would have the type of the final element

* if an if has a concrete element in one arm, make it have that type as a result, even if the if condition is unreachable, to parallel block

* make type rules for brs and switches simpler, ignore whether they are reachable or not. whether they are dead code should not affect how they influence other types in our IR.

1 files changed, 20 insertions, 2 deletions

diff --git a/test/polymorphic_stack.wast b/test/polymorphic_stack.wast
index 1b2459148..d0b9986ba 100644
--- a/test/polymorphic_stack.wast
+++ b/test/polymorphic_stack.wast
@@ -80,7 +80,8 @@
   (func $untaken-break-should-have-value (result i32)
     (block $x (result i32)
       (block
-        (br_if $x ;; ok to not have a value, since an untaken branch. but must emit valid binary for wasm
+        (br_if $x
+          (i32.const 0)
           (unreachable)
         )
       )
@@ -95,6 +96,7 @@
    )
    (block $label$0 (result i32)
     (br_if $label$0
+     (i32.const 0)
      (return
       (i32.const -32)
      )
@@ -103,7 +105,7 @@
   )
   (func $br_table_unreachable_to_also_unreachable (result i32)
     (block $a (result i32)
-      (block $b
+      (block $b (result i32)
         (br_table $a $b ;; seems to send a value, but is not taken
           (unreachable)
           (unreachable)
@@ -111,5 +113,21 @@
       )
     )
   )
+  (func $untaken-br_if (result i32)
+    (block $label$8 (result i32)
+     (block $label$9
+      (drop
+       (if
+        (i32.const 0)
+        (br_if $label$8
+         (unreachable)
+         (i32.const 0)
+        )
+        (unreachable)
+       )
+      )
+     )
+    )
+  )
 )