/** Possible flags for the Operator Scalar Replacement. */
typedef enum osr_flags {
osr_flag_none = 0, /**< no additional flags */
- osr_flag_lftr_with_ov_check = 1, /**< do only linear function test replacement
- if no overflow occurs. */
+ osr_flag_lftr_with_ov_check = 1, /**< do linear function test replacement
+ only if no overflow can occur. */
} osr_flags;
/* FirmJNI cannot handle identical enum values... */
* The linear function replacement test is controlled by the flags.
* If the osr_flag_lftr_with_ov_check is set, the replacement is only
* done if do overflow can occur.
- * Otherwise it is ALWAYS done which might be unsure.
+ * Otherwise it is ALWAYS done which might be insecure.
*
* For instance:
*
*
* because of overflow.
*
+ * More bad cases:
+ *
+ * for (i = 0; i <= 0xF; ++i)
+ *
+ * will NOT be transformed into
+ *
+ * for (i = 0xFFFFFFF0; i <= 0xFFFFFFFF; ++i)
+ *
+ * although here is no direct overflow. The OV occurs when the ++i
+ * is executed (and would created an endless loop here!).
+ *
+ * For the same reason, a loop
+ *
+ * for (i = 0; i <= 9; i += x)
+ *
+ * will NOT be transformed because we cannot estimate whether an overflow
+ * might happen adding x.
+ *
* Note that i < a + 400 is also not possible with the current implementation
* although this might be allowed by other compilers...
+ *
+ * Note further that tests for equality can be handled some simplier (but are not
+ * implemented yet).
+ *
+ * This algorithm destoyes the link field of nodes.
*/
void opt_osr(ir_graph *irg, unsigned flags);