1 files changed, 35 insertions, 0 deletions
diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index c54960079..59a38eeaa 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -350,6 +350,41 @@ struct OptimizeInstructions
           return inner;
         }
       }
+      {
+        // x <<>> (C & (31 | 63))   ==>   x <<>> C'
+        // x <<>> (y & (31 | 63))   ==>   x <<>> y
+        // where '<<>>':
+        //   '<<', '>>', '>>>'. 'rotl' or 'rotr'
+        BinaryOp op;
+        Const* c;
+        Expression *x, *y;
+
+        // x <<>> C
+        if (matches(curr, binary(&op, any(&x), ival(&c))) &&
+            Abstract::hasAnyShift(op)) {
+          // truncate RHS constant to effective size as:
+          // i32(x) <<>> const(C & 31))
+          // i64(x) <<>> const(C & 63))
+          c->value = c->value.and_(
+            Literal::makeFromInt32(c->type.getByteSize() * 8 - 1, c->type));
+          // x <<>> 0   ==>   x
+          if (c->value.isZero()) {
+            return x;
+          }
+        }
+        if (matches(
+              curr,
+              binary(&op, any(&x), binary(Abstract::And, any(&y), ival(&c)))) &&
+            Abstract::hasAnyShift(op)) {
+          // i32(x) <<>> (y & 31)   ==>   x <<>> y
+          // i64(x) <<>> (y & 63)   ==>   x <<>> y
+          if ((c->type == Type::i32 && (c->value.geti32() & 31) == 31) ||
+              (c->type == Type::i64 && (c->value.geti64() & 63LL) == 63LL)) {
+            curr->cast<Binary>()->right = y;
+            return curr;
+          }
+        }
+      }
     }
 
     if (auto* select = curr->dynCast<Select>()) {