file include/tvm/logging.h from AutoTensorize work (#1015)

include/tvm/logging.h

+/*!
+ *  Copyright (c) 2018 by Contributors
+ * \file logging.h
+ * \brief logging utilities on top of dmlc-core
+ */
+#ifndef TVM_LOGGING_H_
+#define TVM_LOGGING_H_
+
+// a technique that enables overriding macro names on the number of parameters. This is used
+// to define other macros below
+#define GET_MACRO(_1, _2, _3, _4, _5, NAME, ...) NAME
+
+/*!
+ * \brief COND_X calls COND_X_N where N is the number of parameters passed to COND_X
+ * X can be any of CHECK_GE, CHECK_EQ, CHECK, or LOG (defined dmlc-core/include/dmlc/logging.h.)
+ * COND_X (but not COND_X_N) are supposed to be used outside this file.
+ * The first parameter of COND_X (and therefore, COND_X_N), which we call 'quit_on_assert',
+ * is a boolean. The rest of the parameters of COND_X is the same as the parameters of X.
+ * quit_on_assert determines the overall behaviour of COND_X. If it's true COND_X
+ * quits the program on assertion failure. If it's false, then it moves on and somehow reports
+ * the assertion failure back to the macro caller in an appropriate manner (e.g, 'return false'
+ * in a function, or 'continue' or 'break' in a loop)
+ * The default behavior when quit_on_assertion is false, is to 'return false'. If this is not
+ * desirable, the macro caller can pass one more last parameter to COND_X to tell COND_X what
+ * to do when when quit_on_assertion is false and the assertion fails.
+ *
+ * Rationale: These macros were designed to implement functions that have two behaviours
+ * in a concise way. Those behaviours are quitting on assertion failures, or trying to
+ * move on from assertion failures. Note that these macros hide lots of control flow in them,
+ * and therefore, makes the logic of the whole code slightly harder to understand. However,
+ * in pieces of code that use these macros frequently, it will significantly shorten the
+ * amount of code needed to be read, and we won't need to clutter the main logic of the
+ * function by repetitive control flow structure. The first problem
+ * mentioned will be improved over time as the developer gets used to the macro.
+ *
+ * Here is an example of how to use it
+ * \code
+ * bool f(..., bool quit_on_assertion) {
+ *   int a = 0, b = 0;
+ *   ...
+ *   a = ...
+ *   b = ...
+ *   // if quit_on_assertion is true, if a==b, continue, otherwise quit.
+ *   // if quit_on_assertion is false, if a==b, continue, otherwise 'return false' (default behaviour)
+ *   COND_CHECK_EQ(quit_on_assertion, a, b) << "some error message when  quiting"
+ *   ...
+ *   for (int i = 0; i < N; i++) {
+ *     a = ...
+ *     b = ...
+ *     // if quit_on_assertion is true, if a==b, continue, otherwise quit.
+ *     // if quit_on_assertion is false, if a==b, continue, otherwise 'break' (non-default
+ *     // behaviour, therefore, has to be explicitly specified)
+ *     COND_CHECK_EQ(quit_on_assertion, a, b, break) << "some error message when  quiting"
+ *   }
+ * }
+ * \endcode
+ */
+#define COND_CHECK_GE(...) \
+  GET_MACRO(__VA_ARGS__, COND_CHECK_GE_5, COND_CHECK_GE_4, COND_CHECK_GE_3)(__VA_ARGS__)
+#define COND_CHECK_EQ(...) \
+  GET_MACRO(__VA_ARGS__, COND_CHECK_EQ_5, COND_CHECK_EQ_4, COND_CHECK_EQ_3)(__VA_ARGS__)
+#define COND_CHECK(...) \
+  GET_MACRO(__VA_ARGS__, COND_CHECK_5, COND_CHECK_4, COND_CHECK_3, COND_CHECK_2)(__VA_ARGS__)
+#define COND_LOG(...) \
+  GET_MACRO(__VA_ARGS__, COND_LOG_5, COND_LOG_4, COND_LOG_3, COND_LOG_2)(__VA_ARGS__)
+
+// Not supposed to be used by users directly.
+#define COND_CHECK_OP(quit_on_assert, x, y, what, op) \
+  if (!quit_on_assert) { \
+    if (!((x) op (y))) \
+      what; \
+  } \
+  else /* NOLINT(*) */ \
+    CHECK_##op(x, y)
+
+#define COND_CHECK_EQ_4(quit_on_assert, x, y, what) COND_CHECK_OP(quit_on_assert, x, y, what, ==)
+#define COND_CHECK_GE_4(quit_on_assert, x, y, what) COND_CHECK_OP(quit_on_assert, x, y, what, >=)
+
+#define COND_CHECK_3(quit_on_assert, x, what) \
+  if (!quit_on_assert) { \
+    if (!(x)) \
+      what; \
+  } \
+  else /* NOLINT(*) */ \
+    CHECK(x)
+
+#define COND_LOG_3(quit_on_assert, x, what) \
+  if (!quit_on_assert) { \
+    what; \
+  } \
+  else /* NOLINT(*) */ \
+    LOG(x)
+
+#define COND_CHECK_EQ_3(quit_on_assert, x, y) COND_CHECK_EQ_4(quit_on_assert, x, y, return false)
+#define COND_CHECK_GE_3(quit_on_assert, x, y) COND_CHECK_GE_4(quit_on_assert, x, y, return false)
+#define COND_CHECK_2(quit_on_assert, x) COND_CHECK_3(quit_on_assert, x, return false)
+#define COND_LOG_2(quit_on_assert, x) COND_LOG_3(quit_on_assert, x, return false)
+
+#endif   // TVM_LOGGING_H_