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, 10 insertions, 8 deletions

diff --git a/tcg/tcg-op.h b/tcg/tcg-op.h
index 8100a5a2e0..8d1da2b670 100644
--- a/tcg/tcg-op.h
+++ b/tcg/tcg-op.h
@@ -401,10 +401,10 @@ static inline void tcg_gen_helperN(void *func, int flags, int sizemask,
 }
 
 /* Note: Both tcg_gen_helper32() and tcg_gen_helper64() are currently
-   reserved for helpers in tcg-runtime.c. These helpers are all const
-   and pure, hence the call to tcg_gen_callN() with TCG_CALL_CONST |
-   TCG_CALL_PURE. This may need to be adjusted if these functions
-   start to be used with other helpers. */
+   reserved for helpers in tcg-runtime.c. These helpers all do not read
+   globals and do not have side effects, hence the call to tcg_gen_callN()
+   with TCG_CALL_NO_READ_GLOBALS | TCG_CALL_NO_SIDE_EFFECTS. This may need
+   to be adjusted if these functions start to be used with other helpers. */
 static inline void tcg_gen_helper32(void *func, int sizemask, TCGv_i32 ret,
                                     TCGv_i32 a, TCGv_i32 b)
 {
@@ -413,8 +413,9 @@ static inline void tcg_gen_helper32(void *func, int sizemask, TCGv_i32 ret,
     fn = tcg_const_ptr(func);
     args[0] = GET_TCGV_I32(a);
     args[1] = GET_TCGV_I32(b);
-    tcg_gen_callN(&tcg_ctx, fn, TCG_CALL_CONST | TCG_CALL_PURE, sizemask,
-                  GET_TCGV_I32(ret), 2, args);
+    tcg_gen_callN(&tcg_ctx, fn,
+                  TCG_CALL_NO_READ_GLOBALS | TCG_CALL_NO_SIDE_EFFECTS,
+                  sizemask, GET_TCGV_I32(ret), 2, args);
     tcg_temp_free_ptr(fn);
 }
 
@@ -426,8 +427,9 @@ static inline void tcg_gen_helper64(void *func, int sizemask, TCGv_i64 ret,
     fn = tcg_const_ptr(func);
     args[0] = GET_TCGV_I64(a);
     args[1] = GET_TCGV_I64(b);
-    tcg_gen_callN(&tcg_ctx, fn, TCG_CALL_CONST | TCG_CALL_PURE, sizemask,
-                  GET_TCGV_I64(ret), 2, args);
+    tcg_gen_callN(&tcg_ctx, fn,
+                  TCG_CALL_NO_READ_GLOBALS | TCG_CALL_NO_SIDE_EFFECTS,
+                  sizemask, GET_TCGV_I64(ret), 2, args);
     tcg_temp_free_ptr(fn);
 }