tcg: rework TCG helper flags

The current helper flags, TCG_CALL_CONST and TCG_CALL_PURE might be
confusing and doesn't provide enough granularity for some helpers (FP
helpers for example).

This patch changes them into the following helpers flags:
- TCG_CALL_NO_READ_GLOBALS means that the helper does not read globals,
  either directly or via an exception. They will not be saved to their
  canonical location before calling the helper.
- TCG_CALL_NO_WRITE_GLOBALS means that the helper does not modify any
  globals. They will only be saved to their canonical locations before
  calling helpers, but they won't be reloaded afterwise.
- TCG_CALL_NO_SIDE_EFFECTS means that the call to the function is
  removed if the return value is not used.

It provides convenience flags, to avoid helper definitions longer than
80 characters. It also provides compatibility flags, and updates the
documentation.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 18 insertions, 8 deletions

diff --git a/tcg/tcg.h b/tcg/tcg.h
index 4b44ecdccb..96b62229c2 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -253,14 +253,24 @@ typedef int TCGv_i64;
 #define TCGV_UNUSED_I64(x) x = MAKE_TCGV_I64(-1)
 
 /* call flags */
-/* A pure function only reads its arguments and TCG global variables
-   and cannot raise exceptions. Hence a call to a pure function can be
-   safely suppressed if the return value is not used. */
-#define TCG_CALL_PURE           0x0010 
-/* A const function only reads its arguments and does not use TCG
-   global variables. Hence a call to such a function does not
-   save TCG global variables back to their canonical location. */
-#define TCG_CALL_CONST          0x0020
+/* Helper does not read globals (either directly or through an exception). It
+   implies TCG_CALL_NO_WRITE_GLOBALS. */
+#define TCG_CALL_NO_READ_GLOBALS    0x0010
+/* Helper does not write globals */
+#define TCG_CALL_NO_WRITE_GLOBALS   0x0020
+/* Helper can be safely suppressed if the return value is not used. */
+#define TCG_CALL_NO_SIDE_EFFECTS    0x0040
+
+/* convenience version of most used call flags */
+#define TCG_CALL_NO_RWG         TCG_CALL_NO_READ_GLOBALS
+#define TCG_CALL_NO_WG          TCG_CALL_NO_WRITE_GLOBALS
+#define TCG_CALL_NO_SE          TCG_CALL_NO_SIDE_EFFECTS
+#define TCG_CALL_NO_RWG_SE      (TCG_CALL_NO_RWG | TCG_CALL_NO_SE)
+#define TCG_CALL_NO_WG_SE       (TCG_CALL_NO_WG | TCG_CALL_NO_SE)
+
+/* compatibility call flags, they should be eventually be removed */
+#define TCG_CALL_PURE           TCG_CALL_NO_SIDE_EFFECTS
+#define TCG_CALL_CONST          TCG_CALL_NO_READ_GLOBALS
 
 /* used to align parameters */
 #define TCG_CALL_DUMMY_TCGV     MAKE_TCGV_I32(-1)