commit 78505279665e64d28e4a308818b69e6f77ecc5d2
author Aurelien Jarno <aurelien@aurel32.net> Tue Oct 09 21:53:08 2012 +0200
committer Aurelien Jarno <aurelien@aurel32.net> Sun Oct 28 14:54:23 2012 +0100
tree 92a449ff75f77f4dcc04b5705a50beaa851c0a76
parent 3d5c5f876d171983d614925eebe4f0edccbb75be

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>

tcg/tcg.c

diff --git a/tcg/tcg.c b/tcg/tcg.c
index c9c6423..c3a7f19 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -1251,7 +1251,7 @@
 
                 /* pure functions can be removed if their result is not
                    used */
-                if (call_flags & TCG_CALL_PURE) {
+                if (call_flags & TCG_CALL_NO_SIDE_EFFECTS) {
                     for(i = 0; i < nb_oargs; i++) {
                         arg = args[i];
                         if (!dead_temps[arg] || mem_temps[arg]) {
@@ -1277,11 +1277,15 @@
                         dead_temps[arg] = 1;
                         mem_temps[arg] = 0;
                     }
-                    
-                    if (!(call_flags & TCG_CALL_CONST)) {
+
+                    if (!(call_flags & TCG_CALL_NO_READ_GLOBALS)) {
+                        /* globals should be synced to memory */
+                        memset(mem_temps, 1, s->nb_globals);
+                    }
+                    if (!(call_flags & (TCG_CALL_NO_WRITE_GLOBALS |
+                                        TCG_CALL_NO_READ_GLOBALS))) {
                         /* globals should go back to memory */
                         memset(dead_temps, 1, s->nb_globals);
-                        memset(mem_temps, 1, s->nb_globals);
                     }
 
                     /* input args are live */
@@ -2128,10 +2132,14 @@
             tcg_reg_free(s, reg);
         }
     }
-    
-    /* store globals and free associated registers (we assume the call
-       can modify any global. */
-    if (!(flags & TCG_CALL_CONST)) {
+
+    /* Save globals if they might be written by the helper, sync them if
+       they might be read. */
+    if (flags & TCG_CALL_NO_READ_GLOBALS) {
+        /* Nothing to do */
+    } else if (flags & TCG_CALL_NO_WRITE_GLOBALS) {
+        sync_globals(s, allocated_regs);
+    } else {
         save_globals(s, allocated_regs);
     }