handle squared shifts of an unreachable

Author: kripken

src/passes/OptimizeInstructions.cpp

@@ -539,9 +539,9 @@ struct OptimizeInstructions : public WalkerPass<PostWalker<OptimizeInstructions,
                 // shifts only use an effective amount from the constant, so adding must
                 // be done carefully
                 auto total = Bits::getEffectiveShifts(leftRight) + Bits::getEffectiveShifts(right);
-                if (total == Bits::getEffectiveShifts(total, left->type)) {
+                if (total == Bits::getEffectiveShifts(total, right->type)) {
                   // no overflow, we can do this
-                  leftRight->value = LiteralUtils::makeLiteralFromInt32(total, left->type);
+                  leftRight->value = LiteralUtils::makeLiteralFromInt32(total, right->type);
                   return left;
                 } // TODO: handle overflows
               }

test/passes/optimize-instructions.txt

@@ -2055,4 +2055,10 @@
    (i64.const 9)
   )
  )
+ (func $shifts-square-unreachable (type $3) (param $x i32) (result i32)
+  (i32.shr_u
+   (unreachable)
+   (i32.const 9)
+  )
+ )
 )

test/passes/optimize-instructions.wast

@@ -2487,4 +2487,13 @@
     (i64.const 4098) ;; 2 bits effectively
    )
   )
+  (func $shifts-square-unreachable (param $x i32) (result i32)
+   (i32.shr_u
+    (i32.shr_u
+     (unreachable)
+     (i32.const 1031) ;; 7 bits effectively
+    )
+    (i32.const 4098) ;; 2 bits effectively
+   )
+  )
 )