From 10b32d661108fb4ec2cb32cf36a074e67455f89e Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Sat, 30 Jan 2016 20:37:09 -0800
Subject: [PATCH 1/8] Put br_if conditions last.

This implements the second half of https://github.com/WebAssembly/design/pull/489.

Desugaring br_if to if+break was fairly awkward; adding br_if to the kernel
language was straightforward and avoided the awkwardness.

This change happened to expose an aspect of `br_if`'s type checking which
differed from my expectations, so I've taken the liberty of fixing that
too. See the deleted assert_invalid in test/labels.wast and the added
$br_if1 testcase. `br_if` either sends its value to the destination label
or to its own result.
---
 ml-proto/host/parser.mly  |  3 ++-
 ml-proto/spec/ast.ml      |  2 +-
 ml-proto/spec/check.ml    |  5 +++++
 ml-proto/spec/desugar.ml  |  6 ++++--
 ml-proto/spec/eval.ml     |  5 +++++
 ml-proto/spec/kernel.ml   |  1 +
 ml-proto/test/labels.wast | 20 +++++++++++++-------
 7 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/ml-proto/host/parser.mly b/ml-proto/host/parser.mly
index 9d92550205..9da657ac37 100644
--- a/ml-proto/host/parser.mly
+++ b/ml-proto/host/parser.mly
@@ -233,7 +233,8 @@ expr1 :
   | LOOP labeling1 labeling1 expr_list
     { fun c -> let c' = $2 c in let c'' = $3 c' in Loop ($4 c'') }
   | BR var expr_opt { fun c -> Br ($2 c label, $3 c) }
-  | BR_IF expr var expr_opt { fun c -> Br_if ($2 c, $3 c label, $4 c) }
+  | BR_IF expr var { fun c -> Br_if (None, $2 c, $3 c label) }
+  | BR_IF expr expr var { fun c -> Br_if (Some ($2 c), $3 c, $4 c label) }
   | RETURN expr_opt
     { let at1 = ati 1 in
       fun c -> Return (label c ("return" @@ at1) @@ at1, $2 c) }
diff --git a/ml-proto/spec/ast.ml b/ml-proto/spec/ast.ml
index 086837736d..0b2239c043 100644
--- a/ml-proto/spec/ast.ml
+++ b/ml-proto/spec/ast.ml
@@ -19,7 +19,7 @@ and expr' =
   | Block of expr list
   | Loop of expr list
   | Br of var * expr option
-  | Br_if of expr * var * expr option
+  | Br_if of expr option * expr * var
   | Return of var * expr option
   | If of expr * expr
   | If_else of expr * expr * expr
diff --git a/ml-proto/spec/check.ml b/ml-proto/spec/check.ml
index fdd19b6830..f170b48b5e 100644
--- a/ml-proto/spec/check.ml
+++ b/ml-proto/spec/check.ml
@@ -133,6 +133,11 @@ let rec check_expr c et e =
   | Break (x, eo) ->
     check_expr_opt c (label c x) eo e.at
 
+  | Br_if (eo, e, x) ->
+    check_expr_opt c (label c x) eo e.at;
+    check_expr c (Some Int32Type) e;
+    check_type (label c x) et e.at
+
   | If (e1, e2, e3) ->
     check_expr c (Some Int32Type) e1;
     check_expr c et e2;
diff --git a/ml-proto/spec/desugar.ml b/ml-proto/spec/desugar.ml
index bad75cc63b..4c3024d34e 100644
--- a/ml-proto/spec/desugar.ml
+++ b/ml-proto/spec/desugar.ml
@@ -17,6 +17,9 @@ and shift' n = function
   | Break (x, eo) ->
     let x' = if x.it < n then x else (x.it + 1) @@ x.at in
     Break (x', Lib.Option.map (shift n) eo)
+  | Br_if (eo, e, x) ->
+    let x' = if x.it < n then x else (x.it + 1) @@ x.at in
+    Br_if (Lib.Option.map (shift n) eo, shift n e, x')
   | If (e1, e2, e3) -> If (shift n e1, shift n e2, shift n e3)
   | Switch (e, xs, x, es) -> Switch (shift n e, xs, x, List.map (shift n) es)
   | Call (x, es) -> Call (x, List.map (shift n) es)
@@ -53,8 +56,7 @@ and expr' at = function
   | Ast.Block es -> Block (List.map expr es)
   | Ast.Loop es -> Block [Loop (seq es) @@ at]
   | Ast.Br (x, eo) -> Break (x, Lib.Option.map expr eo)
-  | Ast.Br_if (e, x, eo) ->
-    If (expr e, Break (x, Lib.Option.map expr eo) @@ at, opt eo)
+  | Ast.Br_if (eo, e, x) -> Br_if (Lib.Option.map expr eo, expr e, x)
   | Ast.Return (x, eo) -> Break (x, Lib.Option.map expr eo)
   | Ast.If (e1, e2) -> If (expr e1, expr e2, Nop @@ Source.after e2.at)
   | Ast.If_else (e1, e2, e3) -> If (expr e1, expr e2, expr e3)
diff --git a/ml-proto/spec/eval.ml b/ml-proto/spec/eval.ml
index 601fbf0b00..0d53c575ee 100644
--- a/ml-proto/spec/eval.ml
+++ b/ml-proto/spec/eval.ml
@@ -154,6 +154,11 @@ let rec eval_expr (c : config) (e : expr) =
   | Break (x, eo) ->
     raise (label c x (eval_expr_opt c eo))
 
+  | Br_if (eo, e, x) ->
+    let i = int32 (eval_expr c e) e.at in
+    let v = eval_expr_opt c eo in
+    if i <> 0l then raise (label c x (eval_expr_opt c eo)) else v
+
   | If (e1, e2, e3) ->
     let i = int32 (eval_expr c e1) e1.at in
     eval_expr c (if i <> 0l then e2 else e3)
diff --git a/ml-proto/spec/kernel.ml b/ml-proto/spec/kernel.ml
index 36d70484d4..8ce0db28e0 100644
--- a/ml-proto/spec/kernel.ml
+++ b/ml-proto/spec/kernel.ml
@@ -82,6 +82,7 @@ and expr' =
   | Block of expr list                      (* execute in sequence *)
   | Loop of expr                            (* loop header *)
   | Break of var * expr option              (* break to n-th surrounding label *)
+  | Br_if of expr option * expr * var       (* conditional break *)
   | If of expr * expr * expr                (* conditional *)
   | Switch of expr * var list * var * expr list   (* table switch *)
   | Call of var * expr list                 (* call function *)
diff --git a/ml-proto/test/labels.wast b/ml-proto/test/labels.wast
index 539f4ef3a3..86c3713295 100644
--- a/ml-proto/test/labels.wast
+++ b/ml-proto/test/labels.wast
@@ -90,7 +90,7 @@
     )
   )
 
-  (func $br_if (result i32)
+  (func $br_if0 (result i32)
     (local $i i32)
     (set_local $i (i32.const 0))
     (block $outer
@@ -100,13 +100,16 @@
         (br_if (i32.const 1) $inner)
         (set_local $i (i32.or (get_local $i) (i32.const 0x2)))
       )
-      (br_if (i32.const 0) $outer (set_local $i (i32.or (get_local $i) (i32.const 0x4))))
+      (br_if (set_local $i (i32.or (get_local $i) (i32.const 0x4))) (i32.const 0) $outer)
       (set_local $i (i32.or (get_local $i) (i32.const 0x8)))
-      (br_if (i32.const 1) $outer (set_local $i (i32.or (get_local $i) (i32.const 0x10))))
+      (br_if (set_local $i (i32.or (get_local $i) (i32.const 0x10))) (i32.const 1) $outer)
       (set_local $i (i32.or (get_local $i) (i32.const 0x20)))
     )
   )
 
+  (func $br_if1 (param i32) (result f32)
+    (block $l (f32.neg (block $i (br_if (f32.const 3) (get_local 0) $l)))))
+
   (func $misc1 (result i32)
    (block $l1 (i32.xor (br $l1 (i32.const 1)) (i32.const 2)))
   )
@@ -123,7 +126,8 @@
   (export "loop5" $loop5)
   (export "switch" $switch)
   (export "return" $return)
-  (export "br_if" $br_if)
+  (export "br_if0" $br_if0)
+  (export "br_if1" $br_if1)
   (export "misc1" $misc1)
   (export "misc2" $misc2)
 )
@@ -143,11 +147,13 @@
 (assert_return (invoke "return" (i32.const 0)) (i32.const 0))
 (assert_return (invoke "return" (i32.const 1)) (i32.const 2))
 (assert_return (invoke "return" (i32.const 2)) (i32.const 2))
-(assert_return (invoke "br_if") (i32.const 0x1d))
+(assert_return (invoke "br_if0") (i32.const 0x1d))
+(assert_return (invoke "br_if1" (i32.const 0)) (f32.const -3))
+(assert_return (invoke "br_if1" (i32.const 1)) (f32.const 3))
 (assert_return (invoke "misc1") (i32.const 1))
 (assert_return (invoke "misc2") (i32.const 1))
 
 (assert_invalid (module (func (loop $l (br $l (i32.const 0))))) "arity mismatch")
 (assert_invalid (module (func (block $l (f32.neg (br_if (i32.const 1) $l)) (nop)))) "type mismatch")
-(assert_invalid (module (func (result f32) (block $l (br_if (i32.const 1) $l (f32.const 0))))) "type mismatch")
-
+(assert_invalid (module (func (result i32) (block $l (br_if (f32.const 0) (i32.const 1) $l)))) "type mismatch")
+(assert_invalid (module (func (param i32) (result i32) (block $l (f32.neg (br_if (f32.const 0) (get_local 0) $l))))) "type mismatch")

From a5ab0ac93a9df2ddcf8480e1b4cdb082e11996d2 Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Thu, 4 Feb 2016 15:47:31 -0800
Subject: [PATCH 2/8] Make br_if return ().

---
 ml-proto/spec/check.ml    | 2 +-
 ml-proto/spec/eval.ml     | 2 +-
 ml-proto/test/labels.wast | 9 +++------
 3 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/ml-proto/spec/check.ml b/ml-proto/spec/check.ml
index f170b48b5e..a5fb324bd8 100644
--- a/ml-proto/spec/check.ml
+++ b/ml-proto/spec/check.ml
@@ -136,7 +136,7 @@ let rec check_expr c et e =
   | Br_if (eo, e, x) ->
     check_expr_opt c (label c x) eo e.at;
     check_expr c (Some Int32Type) e;
-    check_type (label c x) et e.at
+    check_type None et e.at
 
   | If (e1, e2, e3) ->
     check_expr c (Some Int32Type) e1;
diff --git a/ml-proto/spec/eval.ml b/ml-proto/spec/eval.ml
index 0d53c575ee..b9269657c4 100644
--- a/ml-proto/spec/eval.ml
+++ b/ml-proto/spec/eval.ml
@@ -157,7 +157,7 @@ let rec eval_expr (c : config) (e : expr) =
   | Br_if (eo, e, x) ->
     let i = int32 (eval_expr c e) e.at in
     let v = eval_expr_opt c eo in
-    if i <> 0l then raise (label c x (eval_expr_opt c eo)) else v
+    if i <> 0l then raise (label c x (eval_expr_opt c eo)) else None
 
   | If (e1, e2, e3) ->
     let i = int32 (eval_expr c e1) e1.at in
diff --git a/ml-proto/test/labels.wast b/ml-proto/test/labels.wast
index 86c3713295..48cce1fc42 100644
--- a/ml-proto/test/labels.wast
+++ b/ml-proto/test/labels.wast
@@ -107,9 +107,6 @@
     )
   )
 
-  (func $br_if1 (param i32) (result f32)
-    (block $l (f32.neg (block $i (br_if (f32.const 3) (get_local 0) $l)))))
-
   (func $misc1 (result i32)
    (block $l1 (i32.xor (br $l1 (i32.const 1)) (i32.const 2)))
   )
@@ -127,7 +124,6 @@
   (export "switch" $switch)
   (export "return" $return)
   (export "br_if0" $br_if0)
-  (export "br_if1" $br_if1)
   (export "misc1" $misc1)
   (export "misc2" $misc2)
 )
@@ -148,12 +144,13 @@
 (assert_return (invoke "return" (i32.const 1)) (i32.const 2))
 (assert_return (invoke "return" (i32.const 2)) (i32.const 2))
 (assert_return (invoke "br_if0") (i32.const 0x1d))
-(assert_return (invoke "br_if1" (i32.const 0)) (f32.const -3))
-(assert_return (invoke "br_if1" (i32.const 1)) (f32.const 3))
 (assert_return (invoke "misc1") (i32.const 1))
 (assert_return (invoke "misc2") (i32.const 1))
 
 (assert_invalid (module (func (loop $l (br $l (i32.const 0))))) "arity mismatch")
 (assert_invalid (module (func (block $l (f32.neg (br_if (i32.const 1) $l)) (nop)))) "type mismatch")
+
+(assert_invalid (module (func (result f32) (block $l (br_if (f32.const 0) (i32.const 1) $l)))) "type mismatch")
 (assert_invalid (module (func (result i32) (block $l (br_if (f32.const 0) (i32.const 1) $l)))) "type mismatch")
+(assert_invalid (module (func (block $l (f32.neg (br_if (f32.const 0) (i32.const 1) $l))))) "arity mismatch")
 (assert_invalid (module (func (param i32) (result i32) (block $l (f32.neg (br_if (f32.const 0) (get_local 0) $l))))) "type mismatch")

From 3e02d68ce6a8c31df515234a89cf331eeec1d89e Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Thu, 4 Feb 2016 16:26:39 -0800
Subject: [PATCH 3/8] Add another test.

---
 ml-proto/test/labels.wast | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/ml-proto/test/labels.wast b/ml-proto/test/labels.wast
index 48cce1fc42..bd19ebbc6a 100644
--- a/ml-proto/test/labels.wast
+++ b/ml-proto/test/labels.wast
@@ -154,3 +154,6 @@
 (assert_invalid (module (func (result i32) (block $l (br_if (f32.const 0) (i32.const 1) $l)))) "type mismatch")
 (assert_invalid (module (func (block $l (f32.neg (br_if (f32.const 0) (i32.const 1) $l))))) "arity mismatch")
 (assert_invalid (module (func (param i32) (result i32) (block $l (f32.neg (br_if (f32.const 0) (get_local 0) $l))))) "type mismatch")
+(assert_invalid (module (func (param i32) (result f32)
+  (block $l (f32.neg (block $i (br_if (f32.const 3) (get_local 0) $l))))))
+  "type mismatch")

From 81b1a30349b86e092918352c7f63baf6de6841b3 Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Thu, 4 Feb 2016 16:35:04 -0800
Subject: [PATCH 4/8] Fix an unused variable.

---
 ml-proto/spec/eval.ml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ml-proto/spec/eval.ml b/ml-proto/spec/eval.ml
index b9269657c4..9fe92666f6 100644
--- a/ml-proto/spec/eval.ml
+++ b/ml-proto/spec/eval.ml
@@ -157,7 +157,7 @@ let rec eval_expr (c : config) (e : expr) =
   | Br_if (eo, e, x) ->
     let i = int32 (eval_expr c e) e.at in
     let v = eval_expr_opt c eo in
-    if i <> 0l then raise (label c x (eval_expr_opt c eo)) else None
+    if i <> 0l then raise (label c x v) else None
 
   | If (e1, e2, e3) ->
     let i = int32 (eval_expr c e1) e1.at in

From e3d441e662e551e4f0d76eb74027758869e453b9 Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Thu, 4 Feb 2016 17:09:36 -0800
Subject: [PATCH 5/8] Add the testcase from #227.

---
 ml-proto/test/labels.wast | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/ml-proto/test/labels.wast b/ml-proto/test/labels.wast
index bd19ebbc6a..dca28925e1 100644
--- a/ml-proto/test/labels.wast
+++ b/ml-proto/test/labels.wast
@@ -107,6 +107,11 @@
     )
   )
 
+  (func $br_if1 (result i32)
+    (block $l0
+      (br_if (block $l1 (br $l1 (i32.const 1))) (i32.const 1) $l0)
+      (i32.const 1)))
+
   (func $misc1 (result i32)
    (block $l1 (i32.xor (br $l1 (i32.const 1)) (i32.const 2)))
   )
@@ -124,6 +129,7 @@
   (export "switch" $switch)
   (export "return" $return)
   (export "br_if0" $br_if0)
+  (export "br_if1" $br_if1)
   (export "misc1" $misc1)
   (export "misc2" $misc2)
 )
@@ -144,6 +150,7 @@
 (assert_return (invoke "return" (i32.const 1)) (i32.const 2))
 (assert_return (invoke "return" (i32.const 2)) (i32.const 2))
 (assert_return (invoke "br_if0") (i32.const 0x1d))
+(assert_return (invoke "br_if1") (i32.const 1))
 (assert_return (invoke "misc1") (i32.const 1))
 (assert_return (invoke "misc2") (i32.const 1))
 

From 74cf378b9038af3316ddb9be519335ee97ed4c80 Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Thu, 4 Feb 2016 17:17:37 -0800
Subject: [PATCH 6/8] Add more tests from related discussions.

---
 ml-proto/test/labels.wast | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/ml-proto/test/labels.wast b/ml-proto/test/labels.wast
index dca28925e1..6b421d8640 100644
--- a/ml-proto/test/labels.wast
+++ b/ml-proto/test/labels.wast
@@ -112,6 +112,14 @@
       (br_if (block $l1 (br $l1 (i32.const 1))) (i32.const 1) $l0)
       (i32.const 1)))
 
+  (func $br_if2 (result i32)
+    (block $l0
+      (if (i32.const 1)
+        (br $l0
+          (block $l1
+            (br $l1 (i32.const 1)))))
+      (i32.const 1)))
+
   (func $misc1 (result i32)
    (block $l1 (i32.xor (br $l1 (i32.const 1)) (i32.const 2)))
   )
@@ -130,6 +138,7 @@
   (export "return" $return)
   (export "br_if0" $br_if0)
   (export "br_if1" $br_if1)
+  (export "br_if2" $br_if2)
   (export "misc1" $misc1)
   (export "misc2" $misc2)
 )
@@ -151,6 +160,7 @@
 (assert_return (invoke "return" (i32.const 2)) (i32.const 2))
 (assert_return (invoke "br_if0") (i32.const 0x1d))
 (assert_return (invoke "br_if1") (i32.const 1))
+(assert_return (invoke "br_if2") (i32.const 1))
 (assert_return (invoke "misc1") (i32.const 1))
 (assert_return (invoke "misc2") (i32.const 1))
 
@@ -164,3 +174,12 @@
 (assert_invalid (module (func (param i32) (result f32)
   (block $l (f32.neg (block $i (br_if (f32.const 3) (get_local 0) $l))))))
   "type mismatch")
+(assert_invalid (module (func (block $l0 (br_if (nop) (i32.const 1) $l0))))
+  "arity mismatch")
+(assert_invalid (module (func (result i32)
+  (block $l0
+    (if_else (i32.const 1)
+      (br $l0 (block $l1 (br $l1 (i32.const 1))))
+      (block (block $l1 (br $l1 (i32.const 1))) (nop))
+    )
+  (i32.const 1)))) "arity mismatch")

From 6077e09ed6cd2f024fabd4fa2eeae7d111646a2e Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Thu, 4 Feb 2016 18:04:05 -0800
Subject: [PATCH 7/8] Use the desired evaluation order.

---
 ml-proto/spec/eval.ml     |  2 +-
 ml-proto/test/labels.wast | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/ml-proto/spec/eval.ml b/ml-proto/spec/eval.ml
index 9fe92666f6..02d72108d8 100644
--- a/ml-proto/spec/eval.ml
+++ b/ml-proto/spec/eval.ml
@@ -155,8 +155,8 @@ let rec eval_expr (c : config) (e : expr) =
     raise (label c x (eval_expr_opt c eo))
 
   | Br_if (eo, e, x) ->
-    let i = int32 (eval_expr c e) e.at in
     let v = eval_expr_opt c eo in
+    let i = int32 (eval_expr c e) e.at in
     if i <> 0l then raise (label c x v) else None
 
   | If (e1, e2, e3) ->
diff --git a/ml-proto/test/labels.wast b/ml-proto/test/labels.wast
index 6b421d8640..15f27eb0aa 100644
--- a/ml-proto/test/labels.wast
+++ b/ml-proto/test/labels.wast
@@ -120,6 +120,16 @@
             (br $l1 (i32.const 1)))))
       (i32.const 1)))
 
+  (func $br_if3 (result i32)
+    (local $i1 i32)
+    (i32.add (block $l0
+               (br_if (set_local $i1 (i32.const 1))
+                      (set_local $i1 (i32.const 2))
+                      $l0)
+               (i32.const 0))
+             (i32.const 0))
+    (get_local $i1))
+
   (func $misc1 (result i32)
    (block $l1 (i32.xor (br $l1 (i32.const 1)) (i32.const 2)))
   )
@@ -139,6 +149,7 @@
   (export "br_if0" $br_if0)
   (export "br_if1" $br_if1)
   (export "br_if2" $br_if2)
+  (export "br_if3" $br_if3)
   (export "misc1" $misc1)
   (export "misc2" $misc2)
 )
@@ -161,6 +172,7 @@
 (assert_return (invoke "br_if0") (i32.const 0x1d))
 (assert_return (invoke "br_if1") (i32.const 1))
 (assert_return (invoke "br_if2") (i32.const 1))
+(assert_return (invoke "br_if3") (i32.const 2))
 (assert_return (invoke "misc1") (i32.const 1))
 (assert_return (invoke "misc2") (i32.const 1))
 

From 1f85c51fc26165465b2e415ac4646cb28cbdf8c0 Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Fri, 5 Feb 2016 08:10:51 -0800
Subject: [PATCH 8/8] Change the position of the label operand, to be
 consistent with plain br (and calls).

---
 ml-proto/host/parser.mly  |  4 ++--
 ml-proto/spec/ast.ml      |  2 +-
 ml-proto/spec/check.ml    |  2 +-
 ml-proto/spec/desugar.ml  |  6 +++---
 ml-proto/spec/eval.ml     |  2 +-
 ml-proto/spec/kernel.ml   |  2 +-
 ml-proto/test/fac.wast    |  4 ++--
 ml-proto/test/labels.wast | 30 +++++++++++++++---------------
 8 files changed, 26 insertions(+), 26 deletions(-)

diff --git a/ml-proto/host/parser.mly b/ml-proto/host/parser.mly
index 9da657ac37..24875067b8 100644
--- a/ml-proto/host/parser.mly
+++ b/ml-proto/host/parser.mly
@@ -233,8 +233,8 @@ expr1 :
   | LOOP labeling1 labeling1 expr_list
     { fun c -> let c' = $2 c in let c'' = $3 c' in Loop ($4 c'') }
   | BR var expr_opt { fun c -> Br ($2 c label, $3 c) }
-  | BR_IF expr var { fun c -> Br_if (None, $2 c, $3 c label) }
-  | BR_IF expr expr var { fun c -> Br_if (Some ($2 c), $3 c, $4 c label) }
+  | BR_IF var expr { fun c -> Br_if ($2 c label, None, $3 c) }
+  | BR_IF var expr expr { fun c -> Br_if ($2 c label, Some ($3 c), $4 c) }
   | RETURN expr_opt
     { let at1 = ati 1 in
       fun c -> Return (label c ("return" @@ at1) @@ at1, $2 c) }
diff --git a/ml-proto/spec/ast.ml b/ml-proto/spec/ast.ml
index 0b2239c043..4154b859e3 100644
--- a/ml-proto/spec/ast.ml
+++ b/ml-proto/spec/ast.ml
@@ -19,7 +19,7 @@ and expr' =
   | Block of expr list
   | Loop of expr list
   | Br of var * expr option
-  | Br_if of expr option * expr * var
+  | Br_if of var * expr option * expr
   | Return of var * expr option
   | If of expr * expr
   | If_else of expr * expr * expr
diff --git a/ml-proto/spec/check.ml b/ml-proto/spec/check.ml
index a5fb324bd8..42d9c4f7f1 100644
--- a/ml-proto/spec/check.ml
+++ b/ml-proto/spec/check.ml
@@ -133,7 +133,7 @@ let rec check_expr c et e =
   | Break (x, eo) ->
     check_expr_opt c (label c x) eo e.at
 
-  | Br_if (eo, e, x) ->
+  | Br_if (x, eo, e) ->
     check_expr_opt c (label c x) eo e.at;
     check_expr c (Some Int32Type) e;
     check_type None et e.at
diff --git a/ml-proto/spec/desugar.ml b/ml-proto/spec/desugar.ml
index 4c3024d34e..ebd467528e 100644
--- a/ml-proto/spec/desugar.ml
+++ b/ml-proto/spec/desugar.ml
@@ -17,9 +17,9 @@ and shift' n = function
   | Break (x, eo) ->
     let x' = if x.it < n then x else (x.it + 1) @@ x.at in
     Break (x', Lib.Option.map (shift n) eo)
-  | Br_if (eo, e, x) ->
+  | Br_if (x, eo, e) ->
     let x' = if x.it < n then x else (x.it + 1) @@ x.at in
-    Br_if (Lib.Option.map (shift n) eo, shift n e, x')
+    Br_if (x', Lib.Option.map (shift n) eo, shift n e)
   | If (e1, e2, e3) -> If (shift n e1, shift n e2, shift n e3)
   | Switch (e, xs, x, es) -> Switch (shift n e, xs, x, List.map (shift n) es)
   | Call (x, es) -> Call (x, List.map (shift n) es)
@@ -56,7 +56,7 @@ and expr' at = function
   | Ast.Block es -> Block (List.map expr es)
   | Ast.Loop es -> Block [Loop (seq es) @@ at]
   | Ast.Br (x, eo) -> Break (x, Lib.Option.map expr eo)
-  | Ast.Br_if (eo, e, x) -> Br_if (Lib.Option.map expr eo, expr e, x)
+  | Ast.Br_if (x, eo, e) -> Br_if (x, Lib.Option.map expr eo, expr e)
   | Ast.Return (x, eo) -> Break (x, Lib.Option.map expr eo)
   | Ast.If (e1, e2) -> If (expr e1, expr e2, Nop @@ Source.after e2.at)
   | Ast.If_else (e1, e2, e3) -> If (expr e1, expr e2, expr e3)
diff --git a/ml-proto/spec/eval.ml b/ml-proto/spec/eval.ml
index 02d72108d8..403b0859e7 100644
--- a/ml-proto/spec/eval.ml
+++ b/ml-proto/spec/eval.ml
@@ -154,7 +154,7 @@ let rec eval_expr (c : config) (e : expr) =
   | Break (x, eo) ->
     raise (label c x (eval_expr_opt c eo))
 
-  | Br_if (eo, e, x) ->
+  | Br_if (x, eo, e) ->
     let v = eval_expr_opt c eo in
     let i = int32 (eval_expr c e) e.at in
     if i <> 0l then raise (label c x v) else None
diff --git a/ml-proto/spec/kernel.ml b/ml-proto/spec/kernel.ml
index 8ce0db28e0..054ed7666e 100644
--- a/ml-proto/spec/kernel.ml
+++ b/ml-proto/spec/kernel.ml
@@ -82,7 +82,7 @@ and expr' =
   | Block of expr list                      (* execute in sequence *)
   | Loop of expr                            (* loop header *)
   | Break of var * expr option              (* break to n-th surrounding label *)
-  | Br_if of expr option * expr * var       (* conditional break *)
+  | Br_if of var * expr option * expr       (* conditional break *)
   | If of expr * expr * expr                (* conditional *)
   | Switch of expr * var list * var * expr list   (* table switch *)
   | Call of var * expr list                 (* call function *)
diff --git a/ml-proto/test/fac.wast b/ml-proto/test/fac.wast
index 4d19074d12..40459ca95e 100644
--- a/ml-proto/test/fac.wast
+++ b/ml-proto/test/fac.wast
@@ -62,11 +62,11 @@
     (local i64)
     (set_local 1 (i64.const 1))
     (block
-      (br_if (i64.lt_s (get_local 0) (i64.const 2)) 0)
+      (br_if 0 (i64.lt_s (get_local 0) (i64.const 2)))
       (loop
         (set_local 1 (i64.mul (get_local 1) (get_local 0)))
         (set_local 0 (i64.add (get_local 0) (i64.const -1)))
-        (br_if (i64.gt_s (get_local 0) (i64.const 1)) 0)
+        (br_if 0 (i64.gt_s (get_local 0) (i64.const 1)))
       )
     )
     (get_local 1)
diff --git a/ml-proto/test/labels.wast b/ml-proto/test/labels.wast
index 15f27eb0aa..8c51f054c6 100644
--- a/ml-proto/test/labels.wast
+++ b/ml-proto/test/labels.wast
@@ -95,21 +95,21 @@
     (set_local $i (i32.const 0))
     (block $outer
       (block $inner
-        (br_if (i32.const 0) $inner)
+        (br_if $inner (i32.const 0))
         (set_local $i (i32.or (get_local $i) (i32.const 0x1)))
-        (br_if (i32.const 1) $inner)
+        (br_if $inner (i32.const 1))
         (set_local $i (i32.or (get_local $i) (i32.const 0x2)))
       )
-      (br_if (set_local $i (i32.or (get_local $i) (i32.const 0x4))) (i32.const 0) $outer)
+      (br_if $outer (set_local $i (i32.or (get_local $i) (i32.const 0x4))) (i32.const 0))
       (set_local $i (i32.or (get_local $i) (i32.const 0x8)))
-      (br_if (set_local $i (i32.or (get_local $i) (i32.const 0x10))) (i32.const 1) $outer)
+      (br_if $outer (set_local $i (i32.or (get_local $i) (i32.const 0x10))) (i32.const 1))
       (set_local $i (i32.or (get_local $i) (i32.const 0x20)))
     )
   )
 
   (func $br_if1 (result i32)
     (block $l0
-      (br_if (block $l1 (br $l1 (i32.const 1))) (i32.const 1) $l0)
+      (br_if $l0 (block $l1 (br $l1 (i32.const 1))) (i32.const 1))
       (i32.const 1)))
 
   (func $br_if2 (result i32)
@@ -123,9 +123,9 @@
   (func $br_if3 (result i32)
     (local $i1 i32)
     (i32.add (block $l0
-               (br_if (set_local $i1 (i32.const 1))
-                      (set_local $i1 (i32.const 2))
-                      $l0)
+               (br_if $l0
+                      (set_local $i1 (i32.const 1))
+                      (set_local $i1 (i32.const 2)))
                (i32.const 0))
              (i32.const 0))
     (get_local $i1))
@@ -177,16 +177,16 @@
 (assert_return (invoke "misc2") (i32.const 1))
 
 (assert_invalid (module (func (loop $l (br $l (i32.const 0))))) "arity mismatch")
-(assert_invalid (module (func (block $l (f32.neg (br_if (i32.const 1) $l)) (nop)))) "type mismatch")
+(assert_invalid (module (func (block $l (f32.neg (br_if $l (i32.const 1))) (nop)))) "type mismatch")
 
-(assert_invalid (module (func (result f32) (block $l (br_if (f32.const 0) (i32.const 1) $l)))) "type mismatch")
-(assert_invalid (module (func (result i32) (block $l (br_if (f32.const 0) (i32.const 1) $l)))) "type mismatch")
-(assert_invalid (module (func (block $l (f32.neg (br_if (f32.const 0) (i32.const 1) $l))))) "arity mismatch")
-(assert_invalid (module (func (param i32) (result i32) (block $l (f32.neg (br_if (f32.const 0) (get_local 0) $l))))) "type mismatch")
+(assert_invalid (module (func (result f32) (block $l (br_if $l (f32.const 0) (i32.const 1))))) "type mismatch")
+(assert_invalid (module (func (result i32) (block $l (br_if $l (f32.const 0) (i32.const 1))))) "type mismatch")
+(assert_invalid (module (func (block $l (f32.neg (br_if $l (f32.const 0) (i32.const 1)))))) "arity mismatch")
+(assert_invalid (module (func (param i32) (result i32) (block $l (f32.neg (br_if $l (f32.const 0) (get_local 0)))))) "type mismatch")
 (assert_invalid (module (func (param i32) (result f32)
-  (block $l (f32.neg (block $i (br_if (f32.const 3) (get_local 0) $l))))))
+  (block $l (f32.neg (block $i (br_if $l (f32.const 3) (get_local 0)))))))
   "type mismatch")
-(assert_invalid (module (func (block $l0 (br_if (nop) (i32.const 1) $l0))))
+(assert_invalid (module (func (block $l0 (br_if $l0 (nop) (i32.const 1)))))
   "arity mismatch")
 (assert_invalid (module (func (result i32)
   (block $l0