Avoid adding new unneeded names to blocks in text roundtripping (#4943)

Previously the wat parser would turn this input:

(block
  (nop)
)

into something like this:

(block $block17
  (nop)
)

It just added a name all the time, in case the block is referred to by an index
later even though it doesn't have a name.

This PR makes us rountrip more precisely by not adding such names: if there
was no name before, and there is no break by index, then do not add a name.

In addition, this will be useful for non-nullable locals since whether a block has
a name or not matters there. Like #4912, this makes us more regular in our
usage of block names.

1 files changed, 51 insertions, 46 deletions

diff --git a/test/passes/remove-unused-brs_enable-multivalue.txt b/test/passes/remove-unused-brs_enable-multivalue.txt
index cf8ad7ec2..8240bba22 100644
--- a/test/passes/remove-unused-brs_enable-multivalue.txt
+++ b/test/passes/remove-unused-brs_enable-multivalue.txt
@@ -19,10 +19,11 @@
  )
  (func $b1 (param $i1 i32)
   (block $topmost
-   (block $block
+   (block
     (drop
      (i32.const 0)
     )
+    (nop)
    )
   )
  )
@@ -41,10 +42,11 @@
  (func $b4 (param $i1 i32)
   (block $topmost
    (block $inner
-    (block $block
+    (block
      (drop
       (i32.const 0)
      )
+     (nop)
     )
    )
   )
@@ -52,10 +54,11 @@
  (func $b5 (param $i1 i32)
   (block $topmost
    (block $inner
-    (block $block
+    (block
      (drop
       (i32.const 0)
      )
+     (nop)
     )
    )
   )
@@ -69,7 +72,7 @@
  )
  (func $b7 (param $i1 i32)
   (block $topmost
-   (block $block
+   (block
     (drop
      (i32.const 0)
     )
@@ -100,7 +103,7 @@
  (func $b10 (param $i1 i32)
   (block $topmost
    (block $inner
-    (block $block
+    (block
      (drop
       (i32.const 0)
      )
@@ -114,7 +117,7 @@
  (func $b11 (param $i1 i32)
   (block $topmost
    (block $inner
-    (block $block
+    (block
      (drop
       (i32.const 0)
      )
@@ -133,10 +136,11 @@
      (drop
       (i32.const 12)
      )
-     (block $block
+     (block
       (drop
        (i32.const 1)
       )
+      (nop)
      )
     )
    )
@@ -144,10 +148,11 @@
     (drop
      (i32.const 27)
     )
-    (block $block0
+    (block
      (drop
       (i32.const 2)
      )
+     (nop)
     )
    )
   )
@@ -222,10 +227,11 @@
   (if
    (i32.const 18)
    (block $topmost
-    (block $block
+    (block
      (drop
       (i32.const 0)
      )
+     (nop)
     )
    )
   )
@@ -325,7 +331,7 @@
      (i32.const 1)
     )
     (block $block2
-     (block $block
+     (block
       (drop
        (i32.const 2)
       )
@@ -339,7 +345,7 @@
    (if
     (i32.const 0)
     (block $block4
-     (block $block13
+     (block
       (drop
        (i32.const 2)
       )
@@ -355,7 +361,7 @@
    )
    (if
     (block $block6 (result i32)
-     (block $block15
+     (block
       (drop
        (i32.const 2)
       )
@@ -375,17 +381,19 @@
      (i32.const 0)
     )
     (block $a18
-     (block $block19
+     (block
       (drop
        (i32.const 1)
       )
+      (nop)
      )
     )
     (block $a20
-     (block $block21
+     (block
       (drop
        (i32.const 2)
       )
+      (nop)
      )
     )
    )
@@ -396,7 +404,7 @@
   (block $do-once$0
    (if
     (call $b13)
-    (block $block
+    (block
      (drop
       (i32.const 0)
      )
@@ -410,7 +418,7 @@
   (block $do-once$022
    (if
     (call $b13)
-    (block $block24
+    (block
      (drop
       (call $b14)
      )
@@ -424,7 +432,7 @@
   (block $do-once$025
    (if
     (i32.const 0)
-    (block $block27
+    (block
      (drop
       (call $b14)
      )
@@ -516,8 +524,9 @@
    (if
     (i32.const 0)
     (block $out49
-     (block $block
+     (block
       (call $loops)
+      (nop)
      )
     )
     (br $in48)
@@ -560,12 +569,10 @@
    (if
     (i32.const 0)
     (block
-     (block $block61
-      (drop
-       (i32.const 1)
-      )
-      (call $loops)
+     (drop
+      (i32.const 1)
      )
+     (call $loops)
      (br $in58)
     )
     (block $out59
@@ -604,12 +611,10 @@
    (if
     (i32.const 0)
     (block
-     (block $block71
-      (drop
-       (i32.const 1)
-      )
-      (call $loops)
+     (drop
+      (i32.const 1)
      )
+     (call $loops)
      (drop
       (i32.const 102)
      )
@@ -794,7 +799,7 @@
      (if
       (local.get $x)
       (br $out
-       (block $block (result i32)
+       (block (result i32)
         (local.set $x
          (i32.const 0)
         )
@@ -824,7 +829,7 @@
        (i32.const 1)
       )
       (br $out
-       (block $block (result i32)
+       (block (result i32)
         (local.set $x
          (i32.const 0)
         )
@@ -848,7 +853,7 @@
      (if
       (local.get $x)
       (br $out
-       (block $block (result i32)
+       (block (result i32)
         (drop
          (call $if-to-br_if-value-sideeffect
           (i32.const 0)
@@ -963,7 +968,7 @@
        (i32.const 2)
       )
      )
-     (block $block (result i32)
+     (block (result i32)
       (drop
        (call $loop-if)
       )
@@ -2120,7 +2125,7 @@
   (if
    (i32.const 1)
    (block $label
-    (block $block
+    (block
      (drop
       (i32.const 2)
      )
@@ -2135,7 +2140,7 @@
   (block $label
    (if
     (br $label)
-    (block $block
+    (block
      (drop
       (i32.const 2)
      )
@@ -2234,7 +2239,7 @@
   (if
    (i32.const 1)
    (nop)
-   (block $block
+   (block
     (drop
      (loop $label$3 (result i64)
       (br_if $label$3
@@ -2320,7 +2325,9 @@
     (if
      (i32.const 0)
      (block $label$3
-      (block $block
+      (block
+       (nop)
+       (nop)
       )
      )
      (return
@@ -2604,17 +2611,15 @@
   )
  )
  (func $do-not-flow-values-through-unreachable-code (result i32)
-  (block $block
-   (unreachable)
-   (if
-    (i32.const 0)
-    (block $A
-     (return
-      (i32.const 0)
-     )
+  (unreachable)
+  (if
+   (i32.const 0)
+   (block $A
+    (return
+     (i32.const 0)
     )
-    (nop)
    )
+   (nop)
   )
  )
  (func $do-not-flow-values-through-unreachable-code-b (result i32)
@@ -2692,7 +2697,7 @@
      )
      (i32.const 3)
     )
-    (block $block (result i32)
+    (block (result i32)
      (if
       (local.get $x)
       (return