target-xtensa: record available window in TB flags

Record last valid 4-register window pane number in TB flags so that a
window overflow exception throw point is known at the translation time.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>

1 files changed, 11 insertions, 18 deletions

diff --git a/target-xtensa/op_helper.c b/target-xtensa/op_helper.c
index 872e5a823b..49e86343ed 100644
--- a/target-xtensa/op_helper.c
+++ b/target-xtensa/op_helper.c
@@ -251,34 +251,27 @@ void HELPER(entry)(CPUXtensaState *env, uint32_t pc, uint32_t s, uint32_t imm)
 void HELPER(window_check)(CPUXtensaState *env, uint32_t pc, uint32_t w)
 {
     uint32_t windowbase = windowbase_bound(env->sregs[WINDOW_BASE], env);
-    uint32_t windowstart = env->sregs[WINDOW_START];
-    uint32_t m, n;
+    uint32_t windowstart = xtensa_replicate_windowstart(env) >>
+        (env->sregs[WINDOW_BASE] + 1);
+    uint32_t n = ctz32(windowstart) + 1;
 
-    if ((env->sregs[PS] & (PS_WOE | PS_EXCM)) ^ PS_WOE) {
-        return;
-    }
+    assert(n <= w);
 
-    for (n = 1; ; ++n) {
-        if (n > w) {
-            return;
-        }
-        if (windowstart & windowstart_bit(windowbase + n, env)) {
-            break;
-        }
-    }
-
-    m = windowbase_bound(windowbase + n, env);
     rotate_window(env, n);
     env->sregs[PS] = (env->sregs[PS] & ~PS_OWB) |
         (windowbase << PS_OWB_SHIFT) | PS_EXCM;
     env->sregs[EPC1] = env->pc = pc;
 
-    if (windowstart & windowstart_bit(m + 1, env)) {
+    switch (ctz32(windowstart >> n)) {
+    case 0:
         HELPER(exception)(env, EXC_WINDOW_OVERFLOW4);
-    } else if (windowstart & windowstart_bit(m + 2, env)) {
+        break;
+    case 1:
         HELPER(exception)(env, EXC_WINDOW_OVERFLOW8);
-    } else {
+        break;
+    default:
         HELPER(exception)(env, EXC_WINDOW_OVERFLOW12);
+        break;
     }
 }