Fix a bug with (add (sub 0 X) Y) => (sub Y X) (#1727)

We need to verify that the reordering is valid if there are side effects.

Original bug report: https://groups.google.com/forum/?nomobile=true#!topic/emscripten-discuss/HIlGf8o2Ato

1 files changed, 28 insertions, 0 deletions

diff --git a/test/passes/optimize-instructions.wast b/test/passes/optimize-instructions.wast
index aa979c62a..53ed761d8 100644
--- a/test/passes/optimize-instructions.wast
+++ b/test/passes/optimize-instructions.wast
@@ -3526,6 +3526,34 @@
     )
    )
   )
+  (func $add-sub-zero-reorder-1 (param $temp i32) (result i32)
+   (i32.add
+    (i32.add
+     (i32.sub
+      (i32.const 0) ;; this zero looks like we could remove it by subtracting the get of $temp from the parent, but that would reorder it *after* the tee :(
+      (get_local $temp)
+     )
+     (tee_local $temp ;; cannot move this tee before the get
+      (i32.const 1)
+     )
+    )
+    (i32.const 2)
+   )
+  )
+  (func $add-sub-zero-reorder-2 (param $temp i32) (result i32)
+   (i32.add
+    (i32.add
+     (tee_local $temp ;; in this order, the tee already comes first, so all is good for the optimization
+      (i32.const 1)
+     )
+     (i32.sub
+      (i32.const 0)
+      (get_local $temp)
+     )
+    )
+    (i32.const 2)
+   )
+  )
 )
 (module
   (import "env" "memory" (memory $0 (shared 256 256)))