remove unnecessary constraint on remove-unused-br optimization of if-br-* into br_if,* - we can handle a concretely typed if as well, which can happen at the end of a block (#1799)

Author: kripken

src/passes/RemoveUnusedBrs.cpp

@@ -633,7 +633,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
         auto& list = curr->list;
         for (Index i = 0; i < list.size(); i++) {
           auto* iff = list[i]->dynCast<If>();
-          if (!iff || !iff->ifFalse || isConcreteType(iff->type)) continue; // if it lacked an if-false, it would already be a br_if, as that's the easy case
+          if (!iff || !iff->ifFalse) continue; // if it lacked an if-false, it would already be a br_if, as that's the easy case
           auto* ifTrueBreak = iff->ifTrue->dynCast<Break>();
           if (ifTrueBreak && !ifTrueBreak->condition && canTurnIfIntoBrIf(iff->condition, ifTrueBreak->value, passOptions)) {
             // we are an if-else where the ifTrue is a break without a condition, so we can do this

test/lld/hello_world.wast.mem

@@ -938,15 +938,16 @@
   (loop $typed (result i32)
    (block $outer (result i32)
     (block (result i32)
-     (if (result i32)
-      (i32.const 2)
-      (block $block (result i32)
-       (drop
-        (call $loop-if)
-       )
-       (i32.const 0)
+     (br_if $typed
+      (i32.eqz
+       (i32.const 2)
       )
-      (br $typed)
+     )
+     (block $block (result i32)
+      (drop
+       (call $loop-if)
+      )
+      (i32.const 0)
      )
     )
    )
@@ -2382,4 +2383,25 @@
    (br $top)
   )
  )
+ (func $loop-end-set (; 111 ;) (type $10) (param $x i32) (result i32)
+  (loop $loop
+   (nop)
+   (br_if $loop
+    (get_local $x)
+   )
+   (set_local $x
+    (i32.const 1)
+   )
+  )
+  (get_local $x)
+ )
+ (func $loop-end-value (; 112 ;) (type $10) (param $x i32) (result i32)
+  (loop $loop (result i32)
+   (nop)
+   (br_if $loop
+    (get_local $x)
+   )
+   (i32.const 1)
+  )
+ )
 )

test/passes/remove-unused-brs.txt

@@ -1990,5 +1990,26 @@
       (br $top)
     )
   )
+  (func $loop-end-set (param $x i32) (result i32)
+    (loop $loop
+      (nop)
+      (if
+        (get_local $x)
+        (br $loop)
+        (set_local $x (i32.const 1))
+      )
+    )
+    (get_local $x)
+  )
+  (func $loop-end-value (param $x i32) (result i32)
+    (loop $loop (result i32)
+      (nop)
+      (if (result i32)
+        (get_local $x)
+        (br $loop)
+        (i32.const 1)
+      )
+    )
+  )
 )