target/m68k: implement rtd

Add "Return and Deallocate" (rtd) instruction.

  RTD #d

    (SP) -> PC
    SP + 4 + d -> SP

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Tested-By: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Message-Id: <20170605100014.22981-1-laurent@vivier.eu>

target/m68k/cpu.c

@@ -130,6 +130,7 @@ static void m68020_cpu_initfn(Object *obj)
     m68k_set_feature(env, M68K_FEATURE_FPU);
     m68k_set_feature(env, M68K_FEATURE_CAS);
     m68k_set_feature(env, M68K_FEATURE_BKPT);
+    m68k_set_feature(env, M68K_FEATURE_RTD);
 }
 #define m68030_cpu_initfn m68020_cpu_initfn
 #define m68040_cpu_initfn m68020_cpu_initfn
@@ -151,6 +152,7 @@ static void m68060_cpu_initfn(Object *obj)
     m68k_set_feature(env, M68K_FEATURE_FPU);
     m68k_set_feature(env, M68K_FEATURE_CAS);
     m68k_set_feature(env, M68K_FEATURE_BKPT);
+    m68k_set_feature(env, M68K_FEATURE_RTD);
 }
 
 static void m5208_cpu_initfn(Object *obj)

target/m68k/cpu.h

@@ -251,6 +251,7 @@ enum m68k_features {
     M68K_FEATURE_FPU,
     M68K_FEATURE_CAS,
     M68K_FEATURE_BKPT,
+    M68K_FEATURE_RTD,
 };
 
 static inline int m68k_feature(CPUM68KState *env, int feature)

target/m68k/translate.c

@@ -2483,6 +2483,16 @@ DISAS_INSN(nop)
 {
 }
 
+DISAS_INSN(rtd)
+{
+    TCGv tmp;
+    int16_t offset = read_im16(env, s);
+
+    tmp = gen_load(s, OS_LONG, QREG_SP, 0);
+    tcg_gen_addi_i32(QREG_SP, QREG_SP, offset + 4);
+    gen_jmp(s, tmp);
+}
+
 DISAS_INSN(rts)
 {
     TCGv tmp;
@@ -4904,6 +4914,7 @@ void register_m68k_insns (CPUM68KState *env)
     BASE(nop,       4e71, ffff);
     BASE(stop,      4e72, ffff);
     BASE(rte,       4e73, ffff);
+    INSN(rtd,       4e74, ffff, RTD);
     BASE(rts,       4e75, ffff);
     INSN(movec,     4e7b, ffff, CF_ISA_A);
     BASE(jump,      4e80, ffc0);