target/riscv: Use true diff for gen_pc_plus_diff

Reduce reliance on absolute values by using true pc difference for
gen_pc_plus_diff() to prepare for PC-relative translation.

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230526072124.298466-6-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/insn_trans/trans_rvi.c.inc

@@ -158,7 +158,6 @@ static bool gen_branch(DisasContext *ctx, arg_b *a, TCGCond cond)
     TCGLabel *l = gen_new_label();
     TCGv src1 = get_gpr(ctx, a->rs1, EXT_SIGN);
     TCGv src2 = get_gpr(ctx, a->rs2, EXT_SIGN);
-    target_ulong next_pc;
 
     if (get_xl(ctx) == MXL_RV128) {
         TCGv src1h = get_gprh(ctx, a->rs1);
@@ -175,12 +174,11 @@ static bool gen_branch(DisasContext *ctx, arg_b *a, TCGCond cond)
 
     gen_set_label(l); /* branch taken */
 
-    next_pc = ctx->base.pc_next + a->imm;
     if (!has_ext(ctx, RVC) && !ctx->cfg_ptr->ext_zca &&
-        (next_pc & 0x3)) {
+        (a->imm & 0x3)) {
         /* misaligned */
         TCGv target_pc = tcg_temp_new();
-        gen_pc_plus_diff(target_pc, ctx, next_pc);
+        gen_pc_plus_diff(target_pc, ctx, a->imm);
         gen_exception_inst_addr_mis(ctx, target_pc);
     } else {
         gen_goto_tb(ctx, 0, a->imm);

target/riscv/insn_trans/trans_rvzce.c.inc

@@ -297,7 +297,7 @@ static bool trans_cm_jalt(DisasContext *ctx, arg_cm_jalt *a)
      * Update pc to current for the non-unwinding exception
      * that might come from cpu_ld*_code() in the helper.
      */
-    tcg_gen_movi_tl(cpu_pc, ctx->base.pc_next);
+    gen_update_pc(ctx, 0);
     gen_helper_cm_jalt(cpu_pc, cpu_env, tcg_constant_i32(a->index));
 
     /* c.jt vs c.jalt depends on the index. */

target/riscv/translate.c

@@ -226,8 +226,10 @@ static void decode_save_opc(DisasContext *ctx)
 }
 
 static void gen_pc_plus_diff(TCGv target, DisasContext *ctx,
-                             target_ulong dest)
+                             target_long diff)
 {
+    target_ulong dest = ctx->base.pc_next + diff;
+
     if (get_xl(ctx) == MXL_RV32) {
         dest = (int32_t)dest;
     }
@@ -236,7 +238,7 @@ static void gen_pc_plus_diff(TCGv target, DisasContext *ctx,
 
 static void gen_update_pc(DisasContext *ctx, target_long diff)
 {
-    gen_pc_plus_diff(cpu_pc, ctx, ctx->base.pc_next + diff);
+    gen_pc_plus_diff(cpu_pc, ctx, diff);
 }
 
 static void generate_exception(DisasContext *ctx, int excp)
@@ -547,14 +549,11 @@ static void gen_set_fpr_d(DisasContext *ctx, int reg_num, TCGv_i64 t)
 
 static void gen_jal(DisasContext *ctx, int rd, target_ulong imm)
 {
-    target_ulong next_pc;
-
     /* check misaligned: */
-    next_pc = ctx->base.pc_next + imm;
     if (!has_ext(ctx, RVC) && !ctx->cfg_ptr->ext_zca) {
-        if ((next_pc & 0x3) != 0) {
+        if ((imm & 0x3) != 0) {
             TCGv target_pc = tcg_temp_new();
-            gen_pc_plus_diff(target_pc, ctx, next_pc);
+            gen_pc_plus_diff(target_pc, ctx, imm);
             gen_exception_inst_addr_mis(ctx, target_pc);
             return;
         }