target/arm: Use insn_start from DisasContextBase

To keep the multiple update check, replace insn_start
with insn_start_updated.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/arm/tcg/translate-a64.c

@@ -14179,7 +14179,7 @@ static void aarch64_tr_insn_start(DisasContextBase *dcbase, CPUState *cpu)
         pc_arg &= ~TARGET_PAGE_MASK;
     }
     tcg_gen_insn_start(pc_arg, 0, 0);
-    dc->insn_start = tcg_last_op();
+    dc->insn_start_updated = false;
 }
 
 static void aarch64_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)

target/arm/tcg/translate.c

@@ -9273,7 +9273,7 @@ static void arm_tr_insn_start(DisasContextBase *dcbase, CPUState *cpu)
         condexec_bits = (dc->condexec_cond << 4) | (dc->condexec_mask >> 1);
     }
     tcg_gen_insn_start(pc_arg, condexec_bits, 0);
-    dc->insn_start = tcg_last_op();
+    dc->insn_start_updated = false;
 }
 
 static bool arm_check_kernelpage(DisasContext *dc)

target/arm/tcg/translate.h

@@ -165,10 +165,10 @@ typedef struct DisasContext {
     uint8_t gm_blocksize;
     /* True if this page is guarded.  */
     bool guarded_page;
+    /* True if the current insn_start has been updated. */
+    bool insn_start_updated;
     /* Bottom two bits of XScale c15_cpar coprocessor access control reg */
     int c15_cpar;
-    /* TCG op of the current insn_start.  */
-    TCGOp *insn_start;
     /* Offset from VNCR_EL2 when FEAT_NV2 redirects this reg to memory */
     uint32_t nv2_redirect_offset;
 } DisasContext;
@@ -276,10 +276,10 @@ static inline void disas_set_insn_syndrome(DisasContext *s, uint32_t syn)
     syn &= ARM_INSN_START_WORD2_MASK;
     syn >>= ARM_INSN_START_WORD2_SHIFT;
 
-    /* We check and clear insn_start_idx to catch multiple updates.  */
-    assert(s->insn_start != NULL);
-    tcg_set_insn_start_param(s->insn_start, 2, syn);
-    s->insn_start = NULL;
+    /* Check for multiple updates.  */
+    assert(!s->insn_start_updated);
+    s->insn_start_updated = true;
+    tcg_set_insn_start_param(s->base.insn_start, 2, syn);
 }
 
 static inline int curr_insn_len(DisasContext *s)