target/riscv: Minimize the calls to decode_save_opc

The set of instructions that require decode_save_opc for
unwinding is really fairly small -- only insns that can
raise ILLEGAL_INSN at runtime.  This includes CSR, anything
that uses a *new* fp rounding mode, and many privileged insns.

Since unwind info is stored as the difference from the
previous insn, storing a 0 for most insns minimizes the
size of the unwind info.

Booting a debian kernel image to the missing rootfs panic yields

- gen code size       22226819/1026886656
+ gen code size       21601907/1026886656

on 41k TranslationBlocks, a savings of 610kB or a bit less than 3%.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220604231004.49990-4-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

3 files changed, 8 insertions, 0 deletions

diff --git a/target/riscv/insn_trans/trans_privileged.c.inc b/target/riscv/insn_trans/trans_privileged.c.inc
index 53613682e8..46f96ad74d 100644
--- a/target/riscv/insn_trans/trans_privileged.c.inc
+++ b/target/riscv/insn_trans/trans_privileged.c.inc
@@ -75,6 +75,7 @@ static bool trans_sret(DisasContext *ctx, arg_sret *a)
 {
 #ifndef CONFIG_USER_ONLY
     if (has_ext(ctx, RVS)) {
+        decode_save_opc(ctx);
         gen_helper_sret(cpu_pc, cpu_env);
         tcg_gen_exit_tb(NULL, 0); /* no chaining */
         ctx->base.is_jmp = DISAS_NORETURN;
@@ -90,6 +91,7 @@ static bool trans_sret(DisasContext *ctx, arg_sret *a)
 static bool trans_mret(DisasContext *ctx, arg_mret *a)
 {
 #ifndef CONFIG_USER_ONLY
+    decode_save_opc(ctx);
     gen_helper_mret(cpu_pc, cpu_env);
     tcg_gen_exit_tb(NULL, 0); /* no chaining */
     ctx->base.is_jmp = DISAS_NORETURN;
@@ -102,6 +104,7 @@ static bool trans_mret(DisasContext *ctx, arg_mret *a)
 static bool trans_wfi(DisasContext *ctx, arg_wfi *a)
 {
 #ifndef CONFIG_USER_ONLY
+    decode_save_opc(ctx);
     gen_set_pc_imm(ctx, ctx->pc_succ_insn);
     gen_helper_wfi(cpu_env);
     return true;
@@ -113,6 +116,7 @@ static bool trans_wfi(DisasContext *ctx, arg_wfi *a)
 static bool trans_sfence_vma(DisasContext *ctx, arg_sfence_vma *a)
 {
 #ifndef CONFIG_USER_ONLY
+    decode_save_opc(ctx);
     gen_helper_tlb_flush(cpu_env);
     return true;
 #endif
diff --git a/target/riscv/insn_trans/trans_rvh.c.inc b/target/riscv/insn_trans/trans_rvh.c.inc
index cebcb3f8f6..4f8aecddc7 100644
--- a/target/riscv/insn_trans/trans_rvh.c.inc
+++ b/target/riscv/insn_trans/trans_rvh.c.inc
@@ -169,6 +169,7 @@ static bool trans_hfence_gvma(DisasContext *ctx, arg_sfence_vma *a)
 {
     REQUIRE_EXT(ctx, RVH);
 #ifndef CONFIG_USER_ONLY
+    decode_save_opc(ctx);
     gen_helper_hyp_gvma_tlb_flush(cpu_env);
     return true;
 #endif
@@ -179,6 +180,7 @@ static bool trans_hfence_vvma(DisasContext *ctx, arg_sfence_vma *a)
 {
     REQUIRE_EXT(ctx, RVH);
 #ifndef CONFIG_USER_ONLY
+    decode_save_opc(ctx);
     gen_helper_hyp_tlb_flush(cpu_env);
     return true;
 #endif
diff --git a/target/riscv/insn_trans/trans_rvi.c.inc b/target/riscv/insn_trans/trans_rvi.c.inc
index c190a59f22..ca8e3d1ea1 100644
--- a/target/riscv/insn_trans/trans_rvi.c.inc
+++ b/target/riscv/insn_trans/trans_rvi.c.inc
@@ -818,6 +818,8 @@ static bool trans_fence_i(DisasContext *ctx, arg_fence_i *a)
 
 static bool do_csr_post(DisasContext *ctx)
 {
+    /* The helper may raise ILLEGAL_INSN -- record binv for unwind. */
+    decode_save_opc(ctx);
     /* We may have changed important cpu state -- exit to main loop. */
     gen_set_pc_imm(ctx, ctx->pc_succ_insn);
     tcg_gen_exit_tb(NULL, 0);