diff --git a/tcg/README b/tcg/README
index 9d1b100..ec1ac79 100644
--- a/tcg/README
+++ b/tcg/README
@@ -77,11 +77,20 @@ destroyed, but local temporaries and globals are preserved.
 Using the tcg_gen_helper_x_y it is possible to call any function
 taking i32, i64 or pointer types. By default, before calling a helper,
 all globals are stored at their canonical location and it is assumed
-that the function can modify them. This can be overridden by the
-TCG_CALL_CONST function modifier. By default, the helper is allowed to
-modify the CPU state or raise an exception. This can be overridden by
-the TCG_CALL_PURE function modifier, in which case the call to the
-function is removed if the return value is not used.
+that the function can modify them. By default, the helper is allowed to
+modify the CPU state or raise an exception.
+
+This can be overridden using the following function modifiers:
+- 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 locations 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 location 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.
+
+Note that TCG_CALL_NO_READ_GLOBALS implies TCG_CALL_NO_WRITE_GLOBALS.
 
 On some TCG targets (e.g. x86), several calling conventions are
 supported.
diff --git a/tcg/optimize.c b/tcg/optimize.c
index a06c8eb..8e5d918 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -915,7 +915,8 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
 
         case INDEX_op_call:
             nb_call_args = (args[0] >> 16) + (args[0] & 0xffff);
-            if (!(args[nb_call_args + 1] & (TCG_CALL_CONST | TCG_CALL_PURE))) {
+            if (!(args[nb_call_args + 1] & (TCG_CALL_NO_READ_GLOBALS |
+                                            TCG_CALL_NO_WRITE_GLOBALS))) {
                 for (i = 0; i < nb_globals; i++) {
                     reset_temp(i);
                 }
diff --git a/tcg/tcg-op.h b/tcg/tcg-op.h
index 8100a5a..8d1da2b 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);
 }
 
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 @@ static void tcg_liveness_analysis(TCGContext *s)
 
                 /* 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 @@ static void tcg_liveness_analysis(TCGContext *s)
                         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 @@ static int tcg_reg_alloc_call(TCGContext *s, const TCGOpDef *def,
             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);
     }
 
diff --git a/tcg/tcg.h b/tcg/tcg.h
index fb6d9ea..374eb30 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)
