Remove incorrect assertion in IRBuilder (#8177)

IRBuilder has to handle the case where a branching instruction like
br_on_null sends a value to its target label, even though we cannot
directly represent such a value being sent in our IR. To do so, it adds
an extra trampoline label that fetches the sent value out of scratch
locals before branching to the original target.

We previously had an assertion that the scratch local used to hold such
extra values had the same type as the expression with the destination
label. This is usually true, but it is possible that the destination
label is on an If with an unreachable condition, in which case the
destination has type unreachable and the scratch local has the original
concrete label type. Remove the incorrect assertion.

Fixes #8096.

Author: tlively

src/wasm/wasm-ir-builder.cpp

@@ -1166,7 +1166,6 @@ IRBuilder::fixExtraOutput(ScopeCtx& scope, Name label, Expression* curr) {
 
     // If all the received values are in the scratch local, just fetch them out.
     if (receivedType == Type::none) {
-      assert(extraType == labelType);
       curr = builder.makeSequence(
         curr, builder.makeLocalGet(extraLocal, extraType), extraType);
       continue;

test/lit/wat-kitchen-sink.wast

@@ -5139,7 +5139,7 @@
  )
 
  ;; The if is unreachable except through the break; make sure this is
- ;; parse correctly
+ ;; parsed correctly
  ;; CHECK:      (func $if-else-br-return (type $27) (param $a i32) (result i32)
  ;; CHECK-NEXT:  (block $label
  ;; CHECK-NEXT:   (if
@@ -5168,6 +5168,66 @@
   (i32.const 1)
  )
 
+ ;; CHECK:      (func $if-else-unreachable-br-extra (type $1) (result i32)
+ ;; CHECK-NEXT:  (local $scratch nullref)
+ ;; CHECK-NEXT:  (local $scratch_1 i32)
+ ;; CHECK-NEXT:  (local $scratch_2 i32)
+ ;; CHECK-NEXT:  (local $scratch_3 (ref none))
+ ;; CHECK-NEXT:  (local $scratch_4 i32)
+ ;; CHECK-NEXT:  (block $l (result i32)
+ ;; CHECK-NEXT:   (block $l0
+ ;; CHECK-NEXT:    (br $l
+ ;; CHECK-NEXT:     (if (result i32)
+ ;; CHECK-NEXT:      (unreachable)
+ ;; CHECK-NEXT:      (then
+ ;; CHECK-NEXT:       (local.set $scratch_1
+ ;; CHECK-NEXT:        (block (result i32)
+ ;; CHECK-NEXT:         (local.set $scratch_2
+ ;; CHECK-NEXT:          (i32.const 42)
+ ;; CHECK-NEXT:         )
+ ;; CHECK-NEXT:         (local.set $scratch
+ ;; CHECK-NEXT:          (ref.null none)
+ ;; CHECK-NEXT:         )
+ ;; CHECK-NEXT:         (local.get $scratch_2)
+ ;; CHECK-NEXT:        )
+ ;; CHECK-NEXT:       )
+ ;; CHECK-NEXT:       (local.set $scratch_3
+ ;; CHECK-NEXT:        (br_on_null $l0
+ ;; CHECK-NEXT:         (local.get $scratch)
+ ;; CHECK-NEXT:        )
+ ;; CHECK-NEXT:       )
+ ;; CHECK-NEXT:       (local.set $scratch_4
+ ;; CHECK-NEXT:        (local.get $scratch_1)
+ ;; CHECK-NEXT:       )
+ ;; CHECK-NEXT:       (drop
+ ;; CHECK-NEXT:        (local.get $scratch_3)
+ ;; CHECK-NEXT:       )
+ ;; CHECK-NEXT:       (local.get $scratch_4)
+ ;; CHECK-NEXT:      )
+ ;; CHECK-NEXT:      (else
+ ;; CHECK-NEXT:       (i32.const 1337)
+ ;; CHECK-NEXT:      )
+ ;; CHECK-NEXT:     )
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:   (local.get $scratch_1)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $if-else-unreachable-br-extra (result i32)
+  ;; The condition is unreachable, making the if unreachable.
+  unreachable
+  if $l (result i32)
+   ;; Send an extra i32. We should not get confused because the if is
+   ;; unreachable.
+   i32.const 42
+   ref.null none
+   br_on_null $l
+   drop
+  else $l
+   i32.const 1337
+  end $l
+ )
+
  ;; CHECK:      (func $try-br-catch-all-return (type $0)
  ;; CHECK-NEXT:  (block $label
  ;; CHECK-NEXT:   (try