Ordering correction fix in OptimizeInstructions for #3047 (#3195)

(found by the fuzzer)

It is not valid to replace x | (y | x) ==> y | x, if x, y cannot be reordered.

It is also not valid to replace x ^ (y ^ x) ==> y, if x, y cannot be reordered,
for a more subtle reason: if they cannot be reordered then y can affect the
value of x (the opposite is not possible as we checked x for side effects so
that we could remove one copy). If so, then the second appearance of x
could be different, if e.g. it reads a local y writes to. Whereas, if it's ok to
reorder, then it's ok to do x ^ (y ^ x) ==> x ^ (x ^ y) ==> y.

1 files changed, 47 insertions, 1 deletions

diff --git a/test/passes/optimize-instructions_all-features.wast b/test/passes/optimize-instructions_all-features.wast
index c8a48391c..71646de93 100644
--- a/test/passes/optimize-instructions_all-features.wast
+++ b/test/passes/optimize-instructions_all-features.wast
@@ -4805,7 +4805,53 @@
         (local.get $x)
         (local.get $y)
       )
-    ))
+     ))
+    ;; x | (y | x)   where x and y cannot be reordered  -  skip
+    (drop
+      (i32.or
+        (local.get $x)
+        (i32.or
+          (local.tee $x
+            (i32.const 1)
+          )
+          (local.get $x)
+        )
+      )
+    )
+    (drop
+      (i32.or
+        (i32.or
+          (local.get $x)
+          (local.tee $x
+            (i32.const 1)
+          )
+        )
+        (local.get $x)
+      )
+    )
+    ;; x ^ (y ^ x)   where x and y cannot be reordered  -  skip
+    (drop
+      (i32.xor
+        (local.get $x)
+        (i32.xor
+          (local.tee $x
+            (i32.const 1)
+          )
+          (local.get $x)
+        )
+      )
+    )
+    (drop
+      (i32.xor
+        (i32.xor
+          (local.get $x)
+          (local.tee $x
+            (i32.const 1)
+          )
+        )
+        (local.get $x)
+      )
+    )
   )
   (func $optimize-bulk-memory-copy (param $dst i32) (param $src i32) (param $sz i32)
     (memory.copy  ;; skip