target/i386: implement CMPccXADD

The main difficulty here is that a page fault when writing to the destination
must not overwrite the flags.  Therefore, the flags computation must be
inlined instead of using gen_jcc1*.

For simplicity, I am using an unconditional cmpxchg operation, that becomes
a NOP if the comparison fails.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/cpu.c

@@ -738,7 +738,7 @@ void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
 #define TCG_7_0_EDX_FEATURES (CPUID_7_0_EDX_FSRM | CPUID_7_0_EDX_KERNEL_FEATURES)
 
 #define TCG_7_1_EAX_FEATURES (CPUID_7_1_EAX_FZRM | CPUID_7_1_EAX_FSRS | \
-          CPUID_7_1_EAX_FSRC)
+          CPUID_7_1_EAX_FSRC | CPUID_7_1_EAX_CMPCCXADD)
 #define TCG_7_1_EDX_FEATURES 0
 #define TCG_7_2_EDX_FEATURES 0
 #define TCG_APM_FEATURES 0

target/i386/tcg/decode-new.c.inc

@@ -538,6 +538,28 @@ static const X86OpEntry opcodes_0F38_00toEF[240] = {
     [0xdd] = X86_OP_ENTRY3(VAESENCLAST, V,x,  H,x,       W,x,  vex4 cpuid(AES) p_66),
     [0xde] = X86_OP_ENTRY3(VAESDEC,     V,x,  H,x,       W,x,  vex4 cpuid(AES) p_66),
     [0xdf] = X86_OP_ENTRY3(VAESDECLAST, V,x,  H,x,       W,x,  vex4 cpuid(AES) p_66),
+
+    /*
+     * REG selects srcdest2 operand, VEX.vvvv selects src3.  VEX class not found
+     * in manual, assumed to be 13 from the VEX.L0 constraint.
+     */
+    [0xe0] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xe1] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xe2] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xe3] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xe4] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xe5] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xe6] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xe7] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+
+    [0xe8] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xe9] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xea] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xeb] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xec] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xed] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xee] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
+    [0xef] = X86_OP_ENTRY3(CMPccXADD,   M,y, G,y, B,y,  vex13 xchg chk(o64) cpuid(CMPCCXADD) p_66),
 };
 
 /* five rows for no prefix, 66, F3, F2, 66+F2  */
@@ -1503,6 +1525,9 @@ static bool has_cpuid_feature(DisasContext *s, X86CPUIDFeature cpuid)
         return (s->cpuid_7_0_ebx_features & CPUID_7_0_EBX_AVX2);
     case X86_FEAT_SHA_NI:
         return (s->cpuid_7_0_ebx_features & CPUID_7_0_EBX_SHA_NI);
+
+    case X86_FEAT_CMPCCXADD:
+        return (s->cpuid_7_1_eax_features & CPUID_7_1_EAX_CMPCCXADD);
     }
     g_assert_not_reached();
 }

target/i386/tcg/decode-new.h

@@ -104,6 +104,7 @@ typedef enum X86CPUIDFeature {
     X86_FEAT_AVX2,
     X86_FEAT_BMI1,
     X86_FEAT_BMI2,
+    X86_FEAT_CMPCCXADD,
     X86_FEAT_F16C,
     X86_FEAT_FMA,
     X86_FEAT_MOVBE,

target/i386/tcg/emit.c.inc

@@ -1190,6 +1190,110 @@ static void gen_BZHI(DisasContext *s, CPUX86State *env, X86DecodedInsn *decode)
     prepare_update2_cc(decode, s, CC_OP_BMILGB + ot);
 }
 
+static void gen_CMPccXADD(DisasContext *s, CPUX86State *env, X86DecodedInsn *decode)
+{
+    TCGLabel *label_top = gen_new_label();
+    TCGLabel *label_bottom = gen_new_label();
+    TCGv oldv = tcg_temp_new();
+    TCGv newv = tcg_temp_new();
+    TCGv cmpv = tcg_temp_new();
+    TCGCond cond;
+
+    TCGv cmp_lhs, cmp_rhs;
+    MemOp ot, ot_full;
+
+    int jcc_op = (decode->b >> 1) & 7;
+    static const TCGCond cond_table[8] = {
+        [JCC_O] = TCG_COND_LT,  /* test sign bit by comparing against 0 */
+        [JCC_B] = TCG_COND_LTU,
+        [JCC_Z] = TCG_COND_EQ,
+        [JCC_BE] = TCG_COND_LEU,
+        [JCC_S] = TCG_COND_LT,  /* test sign bit by comparing against 0 */
+        [JCC_P] = TCG_COND_EQ,  /* even parity - tests low bit of popcount */
+        [JCC_L] = TCG_COND_LT,
+        [JCC_LE] = TCG_COND_LE,
+    };
+
+    cond = cond_table[jcc_op];
+    if (decode->b & 1) {
+        cond = tcg_invert_cond(cond);
+    }
+
+    ot = decode->op[0].ot;
+    ot_full = ot | MO_LE;
+    if (jcc_op >= JCC_S) {
+        /*
+         * Sign-extend values before subtracting for S, P (zero/sign extension
+         * does not matter there) L, LE and their inverses.
+         */
+        ot_full |= MO_SIGN;
+    }
+
+    /*
+     * cmpv will be moved to cc_src *after* cpu_regs[] is written back, so use
+     * tcg_gen_ext_tl instead of gen_ext_tl.
+     */
+    tcg_gen_ext_tl(cmpv, cpu_regs[decode->op[1].n], ot_full);
+
+    /*
+     * Cmpxchg loop starts here.
+     * - s->T1: addition operand (from decoder)
+     * - s->A0: dest address (from decoder)
+     * - s->cc_srcT: memory operand (lhs for comparison)
+     * - cmpv: rhs for comparison
+     */
+    gen_set_label(label_top);
+    gen_op_ld_v(s, ot_full, s->cc_srcT, s->A0);
+    tcg_gen_sub_tl(s->T0, s->cc_srcT, cmpv);
+
+    /* Compute the comparison result by hand, to avoid clobbering cc_*.  */
+    switch (jcc_op) {
+    case JCC_O:
+        /* (src1 ^ src2) & (src1 ^ dst). newv is only used here for a moment */
+        tcg_gen_xor_tl(newv, s->cc_srcT, s->T0);
+        tcg_gen_xor_tl(s->tmp0, s->cc_srcT, cmpv);
+        tcg_gen_and_tl(s->tmp0, s->tmp0, newv);
+        tcg_gen_sextract_tl(s->tmp0, s->tmp0, 0, 8 << ot);
+        cmp_lhs = s->tmp0, cmp_rhs = tcg_constant_tl(0);
+        break;
+
+    case JCC_P:
+        tcg_gen_ext8u_tl(s->tmp0, s->T0);
+        tcg_gen_ctpop_tl(s->tmp0, s->tmp0);
+        tcg_gen_andi_tl(s->tmp0, s->tmp0, 1);
+        cmp_lhs = s->tmp0, cmp_rhs = tcg_constant_tl(0);
+        break;
+
+    case JCC_S:
+        tcg_gen_sextract_tl(s->tmp0, s->T0, 0, 8 << ot);
+        cmp_lhs = s->tmp0, cmp_rhs = tcg_constant_tl(0);
+        break;
+
+    default:
+        cmp_lhs = s->cc_srcT, cmp_rhs = cmpv;
+        break;
+    }
+
+    /* Compute new value: if condition does not hold, just store back s->cc_srcT */
+    tcg_gen_add_tl(newv, s->cc_srcT, s->T1);
+    tcg_gen_movcond_tl(cond, newv, cmp_lhs, cmp_rhs, newv, s->cc_srcT);
+    tcg_gen_atomic_cmpxchg_tl(oldv, s->A0, s->cc_srcT, newv, s->mem_index, ot_full);
+
+    /* Exit unconditionally if cmpxchg succeeded.  */
+    tcg_gen_brcond_tl(TCG_COND_EQ, oldv, s->cc_srcT, label_bottom);
+
+    /* Try again if there was actually a store to make.  */
+    tcg_gen_brcond_tl(cond, cmp_lhs, cmp_rhs, label_top);
+    gen_set_label(label_bottom);
+
+    /* Store old value to registers only after a successful store.  */
+    gen_writeback(s, decode, 1, s->cc_srcT);
+
+    decode->cc_dst = s->T0;
+    decode->cc_src = cmpv;
+    decode->cc_op = CC_OP_SUBB + ot;
+}
+
 static void gen_CRC32(DisasContext *s, CPUX86State *env, X86DecodedInsn *decode)
 {
     MemOp ot = decode->op[2].ot;

target/i386/tcg/translate.c

@@ -122,6 +122,7 @@ typedef struct DisasContext {
     int cpuid_ext3_features;
     int cpuid_7_0_ebx_features;
     int cpuid_7_0_ecx_features;
+    int cpuid_7_1_eax_features;
     int cpuid_xsave_features;
 
     /* TCG local temps */
@@ -6963,6 +6964,7 @@ static void i386_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cpu)
     dc->cpuid_ext3_features = env->features[FEAT_8000_0001_ECX];
     dc->cpuid_7_0_ebx_features = env->features[FEAT_7_0_EBX];
     dc->cpuid_7_0_ecx_features = env->features[FEAT_7_0_ECX];
+    dc->cpuid_7_1_eax_features = env->features[FEAT_7_1_EAX];
     dc->cpuid_xsave_features = env->features[FEAT_XSAVE];
     dc->jmp_opt = !((cflags & CF_NO_GOTO_TB) ||
                     (flags & (HF_TF_MASK | HF_INHIBIT_IRQ_MASK)));