target/xtensa: only rotate window in the retw helper

Move return address calculation and WINDOW_START adjustment out of the
retw helper to simplify logic a bit and avoid using registers directly.
Pass a0 as a parameter to the helper.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

target/xtensa/helper.h

@@ -7,7 +7,7 @@ DEF_HELPER_1(sync_windowbase, void, env)
 DEF_HELPER_4(entry, void, env, i32, i32, i32)
 DEF_HELPER_2(test_ill_retw, void, env, i32)
 DEF_HELPER_2(test_underflow_retw, void, env, i32)
-DEF_HELPER_2(retw, i32, env, i32)
+DEF_HELPER_2(retw, void, env, i32)
 DEF_HELPER_3(window_check, noreturn, env, i32, i32)
 DEF_HELPER_1(restore_owb, void, env)
 DEF_HELPER_2(movsp, void, env, i32)

target/xtensa/translate.c

@@ -2227,8 +2227,13 @@ static bool test_ill_retw(DisasContext *dc, const uint32_t arg[],
 static void translate_retw(DisasContext *dc, const uint32_t arg[],
                            const uint32_t par[])
 {
-    TCGv_i32 tmp = tcg_const_i32(dc->pc);
-    gen_helper_retw(tmp, cpu_env, tmp);
+    TCGv_i32 tmp = tcg_const_i32(1);
+    tcg_gen_shl_i32(tmp, tmp, cpu_SR[WINDOW_BASE]);
+    tcg_gen_andc_i32(cpu_SR[WINDOW_START],
+                     cpu_SR[WINDOW_START], tmp);
+    tcg_gen_movi_i32(tmp, dc->pc);
+    tcg_gen_deposit_i32(tmp, tmp, cpu_R[0], 0, 30);
+    gen_helper_retw(cpu_env, cpu_R[0]);
     gen_jump(dc, tmp);
     tcg_temp_free(tmp);
 }

target/xtensa/win_helper.c

@@ -184,15 +184,11 @@ void HELPER(test_underflow_retw)(CPUXtensaState *env, uint32_t pc)
     }
 }
 
-uint32_t HELPER(retw)(CPUXtensaState *env, uint32_t pc)
+void HELPER(retw)(CPUXtensaState *env, uint32_t a0)
 {
-    int n = (env->regs[0] >> 30) & 0x3;
-    uint32_t windowbase = windowbase_bound(env->sregs[WINDOW_BASE], env);
-    uint32_t ret_pc = (pc & 0xc0000000) | (env->regs[0] & 0x3fffffff);
+    int n = (a0 >> 30) & 0x3;
 
     xtensa_rotate_window(env, -n);
-    env->sregs[WINDOW_START] &= ~windowstart_bit(windowbase, env);
-    return ret_pc;
 }
 
 void xtensa_restore_owb(CPUXtensaState *env)