s390: Simplify the optimisation for PUTs to tracked registers.

There is no need to treat the guest IA register specially. The first
assignment in a SB to any tracked register will always assign the full value
and not do an incremental update. Therefore, maintaining
env->first_IA_assignment is redundant. Interestingly, the old code
forgot to mark the tracking state as valid when first_IA_assignment was
true, resulting in an inefficiency (in the order of 0.8% of insns).

Also, when a tracked register already contains the value that it is
being assigned, there is not need to
(a) check whether that register requires precise memory exceptions and
(b) if so, assign the new value.
By definition, the register is up-to-date and reassigning the new value
which is also the old value is meaningless. No idea, what I was thinking
at the time.

git-svn-id: svn://svn.valgrind.org/vex/trunk@2614

diff --git a/VEX/priv/host_s390_isel.c b/VEX/priv/host_s390_isel.c
index 209bfb8dacf95ec43b248d5f6b11b768db2e8954..568e4c3b25045e4d179f170f0ef81a10f8a88cb1 100644 (file)
--- a/VEX/priv/host_s390_isel.c
+++ b/VEX/priv/host_s390_isel.c
@@ -38,7 +38,7 @@
 
 #include "main_util.h"
 #include "main_globals.h"
-#include "guest_s390_defs.h"   /* guest_s390x_state_requires_precise_mem_exns */
+#include "guest_s390_defs.h"   /* S390X_GUEST_OFFSET */
 #include "host_generic_regs.h"
 #include "host_s390_defs.h"
 
@@ -82,8 +82,6 @@
      point of the destination, thereby avoiding the destination's
      event check.
 
-    - A flag to indicate whether the guest IA has been assigned to.
-
     - Values of certain guest registers which are often assigned constants.
 */
 
@@ -122,7 +120,6 @@ typedef struct {
    Addr64       max_ga;
    Bool         chaining_allowed;
 
-   Bool         first_IA_assignment;
    Bool         old_value_valid[NUM_TRACKED_REGS];
 } ISelEnv;
 
@@ -2965,20 +2962,6 @@ s390_isel_stmt(ISelEnv *env, IRStmt *stmt)
 
       if (guest_reg == GUEST_UNKNOWN) goto not_special;
 
-      if (guest_reg == GUEST_IA) {
-         /* If this is the first assignment to the IA reg, don't special case
-            it. We need to do a full 8-byte assignment here. The reason is 
-            that in case of a redirected translation the guest IA does not 
-            contain the redirected-to address. Instead it contains the 
-            redirected-from address and those can be far apart. So in order to
-            do incremnetal updates if the IA in the future we need to get the
-            initial address of the super block correct. */
-         if (env->first_IA_assignment) {
-            env->first_IA_assignment = False;
-            goto not_special;
-         }
-      }
-
       if (stmt->Ist.Put.data->tag != Iex_Const) {
          /* Invalidate guest register contents */
          env->old_value_valid[guest_reg] = False;
@@ -2999,12 +2982,9 @@ s390_isel_stmt(ISelEnv *env, IRStmt *stmt)
       env->old_value_valid[guest_reg] = True;
 
       /* If the register already contains the new value, there is nothing
-         to do here. Unless the guest register requires precise memory
-         exceptions. */
+         to do here. */
       if (old_value_is_valid && new_value == old_value) {
-         if (! guest_s390x_state_requires_precise_mem_exns(offset, offset + 8)) {
-            return;
-         }
+         return;
       }
 
       /* guest register = 0 */
@@ -3463,7 +3443,6 @@ iselSB_S390(IRSB *bb, VexArch arch_host, VexArchInfo *archinfo_host,
    env->type_env = bb->tyenv;
 
    /* Set up data structures for tracking guest register values. */
-   env->first_IA_assignment = True;
    for (i = 0; i < NUM_TRACKED_REGS; ++i) {
       env->old_value[i] = 0;  /* just something to have a defined value */
       env->old_value_valid[i] = False;