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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2001:4860:4864:20::35; envelope-from=richard.henderson@linaro.org; helo=mail-oa1-x35.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 10/14/23 03:01, Paolo Bonzini wrote: > +static void gen_CMPccXADD(DisasContext *s, CPUX86State *env, X86DecodedInsn *decode) > +{ > + TCGv z_tl = tcg_constant_tl(0); > + TCGLabel *label_top = gen_new_label(); > + TCGLabel *label_bottom = gen_new_label(); > + TCGv oldv = tcg_temp_new(); > + TCGv memv = tcg_temp_new(); > + TCGv newv = tcg_temp_new(); > + TCGv cmpv = tcg_temp_new(); > + TCGv tmp_cc = tcg_temp_new(); > + > + TCGv cmp_lhs, cmp_rhs; > + MemOp ot, ot_full; > + > + int jcc_op = (decode->b >> 1) & 7; > + static const uint8_t cond[16] = { TCGCond. > + TCG_COND_NE, /* o, just test OF=1 */ > + TCG_COND_EQ, /* no, just test OF=0 */ > + TCG_COND_LTU, /* b */ > + TCG_COND_GEU, /* ae (nb) */ > + TCG_COND_EQ, /* z */ > + TCG_COND_NE, /* nz */ > + TCG_COND_LEU, /* be */ > + TCG_COND_GTU, /* a (nbe) */ > + TCG_COND_LT, /* s, compares result against 0 */ > + TCG_COND_GE, /* ns, compares result against 0 */ > + TCG_COND_NE, /* p, just test PF=1 */ > + TCG_COND_EQ, /* np, just test PF=0 */ > + TCG_COND_LT, /* l */ > + TCG_COND_GE, /* ge (nl) */ > + TCG_COND_LE, /* le */ > + TCG_COND_GT, /* g (nle) */ > + }; You don't need the full table here: cond = cond_table[jcc_op]; if (decode->b & 1) cond = tcg_invert_cond(cond) > + /* Compute comparison result but do not clobber cc_* yet. */ > + switch (jcc_op) { > + case JCC_O: > + case JCC_P: > + tcg_gen_sub_tl(s->T0, memv, cmpv); > + gen_helper_cc_compute_all(tmp_cc, s->T0, cmpv, z_tl, > + tcg_constant_i32(CC_OP_SUBB + ot)); > + decode->cc_src = tmp_cc; > + set_cc_op(s, CC_OP_EFLAGS); > + > + tcg_gen_andi_tl(s->T0, tmp_cc, (jcc_op == JCC_O ? CC_O : CC_P)); > + cmp_lhs = s->T0, cmp_rhs = z_tl; I'm not keen on the weight of the helper function within a cmpxchg loop. I think you should compute these two cases explicitly: JCC_O: // Need operands sign-extended. // cond_table[JCC_O] = TCG_COND_LT -- sign bit set. tcg_gen_xor_tl(tmp, cmpv, memv); tcg_gen_xor_tl(cmp_lhs, cmpv, s->T0); tcg_gen_and_tl(cmp_lhs, cmp_lhs, tmp); cmp_rhs = z_tl; break; JCC_P: // cond_table[JCC_P] = TCG_COND_EQ -- even parity. tcg_gen_ext8u_tl(cmp_lhs, s->T0); tcg_gen_ctpop_tl(cmp_lhs, cmp_lhs); tcg_gen_andi_tl(cmp_lhs, cmp_lhs, 1); cmp_rhs = z_tl; break; > + cc_sub: > + decode->cc_dst = s->T0; > + decode->cc_src = cmpv; > + decode->cc_srcT = memv; > + set_cc_op(s, CC_OP_SUBB + ot); > + break; At which point this is common to all cases. > + } > + > + /* Compute new value: if condition does not hold, just store back memv */ > + tcg_gen_add_tl(newv, memv, s->T1); > + tcg_gen_movcond_tl(cond[decode->b & 15], newv, cmp_lhs, cmp_rhs, newv, memv); > + tcg_gen_atomic_cmpxchg_tl(oldv, s->A0, memv, newv, s->mem_index, ot_full); > + > + /* Exit unconditionally if cmpxchg succeeded. */ > + tcg_gen_brcond_tl(TCG_COND_EQ, oldv, memv, label_bottom); > + > + /* Try again if there was actually a store to make. */ > + tcg_gen_brcond_tl(cond[decode->b & 15], cmp_lhs, cmp_rhs, label_top); I'm tempted to have this unlikely case sync the pc and exit the tb. This would restart the current instruction after testing for exit request. But I suppose we have plenty of other places with unbounded cmpxchg loops... r~