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target/riscv: Minimize the calls to decode_save_opc

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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>
This commit is contained in:
Richard Henderson 2022-06-04 23:10:04 +00:00 • committed by Alistair Francis
parent 5dacdbaeaf
commit a9814e3e08
4 changed files with 17 additions and 9 deletions
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4
target/riscv/insn_trans/trans_privileged.c.inc
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@ -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