[Qemu-devel] [PATCH 6/6] tcg-i386: Implement setcond, movcond, setcond2.

[Richard Henderson]

Implement conditional moves in the i386 backend.

Signed-off-by: Richard Henderson <address@hidden>
---
 tcg/i386/tcg-target.c |  173 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 173 insertions(+), 0 deletions(-)

diff --git a/tcg/i386/tcg-target.c b/tcg/i386/tcg-target.c
index f7b2416..98d667c 100644
--- a/tcg/i386/tcg-target.c
+++ b/tcg/i386/tcg-target.c
@@ -426,6 +426,165 @@ static void tcg_out_brcond2(TCGContext *s, const TCGArg 
*args,
     tcg_out_label(s, label_next, (tcg_target_long)s->code_ptr);
 }
 
+static void tcg_out_setcond(TCGContext *s, int cond, TCGArg arg0,
+                            TCGArg arg1, TCGArg arg2, int const_arg2)
+{
+    int use_xor = (arg0 != arg1 && (const_arg2 || arg0 != arg2));
+
+    if (use_xor)
+        tcg_out_movi(s, TCG_TYPE_I32, arg0, 0);
+    tcg_out_cond(s, cond, arg1, arg2, const_arg2);
+    tcg_out_modrm(s, 0x90 | tcg_cond_to_jcc[cond] | P_EXT, 0, arg0);
+    if (!use_xor)
+        tgen_arithi(s, ARITH_AND, arg0, 0xff, 0);
+}
+
+static void tcg_out_setcond2(TCGContext *s, const TCGArg *args,
+                             const int *const_args)
+{
+    TCGArg new_args[6];
+    int label_true, label_over;
+
+    memcpy(new_args, args+1, 5*sizeof(TCGArg));
+
+    if (args[0] == args[1] || args[0] == args[2]
+        || (!const_args[3] && args[0] == args[3])
+        || (!const_args[4] && args[0] == args[4])) {
+        /* When the destination overlaps with one of the argument
+           registers, don't do anything tricky.  */
+        label_true = gen_new_label();
+        label_over = gen_new_label();
+
+        new_args[5] = label_true;
+        tcg_out_brcond2(s, new_args, const_args+1, 1);
+
+        tcg_out_movi(s, TCG_TYPE_I32, args[0], 0);
+        tcg_out_jxx(s, JCC_JMP, label_over, 1);
+        tcg_out_label(s, label_true, (tcg_target_long)s->code_ptr);
+
+        tcg_out_movi(s, TCG_TYPE_I32, args[0], 1);
+        tcg_out_label(s, label_over, (tcg_target_long)s->code_ptr);
+    } else {
+        /* When the destination does not overlap one of the arguments,
+           clear the destination first, jump if cond false, and emit an
+           increment in the true case.  This results in smaller code.  */
+
+        tcg_out_movi(s, TCG_TYPE_I32, args[0], 0);
+
+        label_over = gen_new_label();
+        new_args[4] = tcg_invert_cond(new_args[4]);
+        new_args[5] = label_over;
+        tcg_out_brcond2(s, new_args, const_args+1, 1);
+
+        tgen_arithi(s, ARITH_ADD, args[0], 1, 0);
+        tcg_out_label(s, label_over, (tcg_target_long)s->code_ptr);
+    }
+}
+
+static inline int have_cmov(void)
+{
+#ifdef __i686__
+    /* Compiler options say that cmov is available.  */
+    return 1;
+#else
+    /* ??? Use cpuid or something and figure out what's running.  */
+    return 0;
+#endif
+}
+
+static void tcg_out_movcond(TCGContext *s, const TCGArg *args,
+                            const int *const_args)
+{
+    int vtc, vfc, cond, use_cmov = 0, do_swap = 0;
+    TCGArg d, vt, vf;
+
+    d = args[0];
+    vt = args[3];
+    vf = args[4];
+    vtc = const_args[3];
+    vfc = const_args[4];
+
+    /* ??? The jcc code path below assumes that one mov insn must be skipped.
+       Rather than complicate the code below, make sure to simplify the
+       conditional move here.  */
+    if (vtc == vfc && vt == vf) {
+        if (vtc)
+            tcg_out_movi(s, TCG_TYPE_I32, d, vt);
+        else
+            tcg_out_mov(s, d, vt);
+        return;
+    }
+
+    cond = args[5];
+
+    /* If both arguments are constants, we *could* do all the funny bits that
+       gcc does with sbc, masks, etc.  There's likely no point.  Just use the
+       jcc version in this case.  We also have to be careful about clobbering
+       inputs when trying to move constants into position.  */
+
+    if (have_cmov()) {
+        use_cmov = 1;
+        if (vtc) {
+            if (vfc || d == vf)
+                use_cmov = 0;
+            else
+                do_swap = 1;
+        } else if (d == vt) {
+            if (vfc)
+                use_cmov = 0;
+            else
+                do_swap = 1;
+        }
+    }
+
+    if (!use_cmov) {
+        /* We're going to follow the lead of cmov and set D=VF first,
+           which means inverting the condition upon which we jump.  */
+        cond = tcg_invert_cond(cond);
+
+        /* Don't allow the move we jump over to be a nop.  */
+        do_swap = (!vtc && d == vt);
+    }
+
+    if (do_swap) {
+        TCGArg t;
+        cond = tcg_invert_cond(cond);
+        t = vf, vf = vt, vt = t;
+        t = vfc, vfc = vtc, vtc = t;
+    }
+
+    /* If possible, set D=0 before the compare, so that we can use XOR.  */
+    if (vfc && vf == 0 && d != args[1] && (const_args[2] || d != args[2])) {
+        tcg_out_movi(s, TCG_TYPE_I32, d, 0);
+        vf = d, vfc = 0;
+    }
+
+    tcg_out_cond(s, cond, args[1], args[2], const_args[2]);
+
+    if (vfc) {
+        /* Force the use of "mov $0, d" to avoid clobbering flags.  */
+        tcg_out8(s, 0xb8 + d);
+        tcg_out32(s, vf);
+    } else {
+        tcg_out_mov(s, d, vf);
+    }
+
+    if (use_cmov) {
+        assert (!vtc);
+        tcg_out_modrm(s, 0x40 | tcg_cond_to_jcc[cond] | P_EXT, d, vt);
+    } else {
+        int label_next = gen_new_label();
+
+        tcg_out_jxx(s, tcg_cond_to_jcc[cond], label_next, 1);
+        if (vtc)
+            tcg_out_movi(s, TCG_TYPE_I32, d, vt);
+        else
+            tcg_out_mov(s, d, vt);
+
+        tcg_out_label(s, label_next, (tcg_target_long)s->code_ptr);
+    }
+}
+
 #if defined(CONFIG_SOFTMMU)
 
 #include "../../softmmu_defs.h"
@@ -1087,6 +1246,16 @@ static inline void tcg_out_op(TCGContext *s, int opc,
         tcg_out_modrm(s, 0xb7 | P_EXT, args[0], args[1]);
         break;
 
+    case INDEX_op_setcond_i32:
+        tcg_out_setcond(s, args[3], args[0], args[1], args[2], const_args[2]);
+        break;
+    case INDEX_op_movcond_i32:
+        tcg_out_movcond(s, args, const_args);
+        break;
+    case INDEX_op_setcond2_i32:
+        tcg_out_setcond2(s, args, const_args);
+        break;
+
     case INDEX_op_qemu_ld8u:
         tcg_out_qemu_ld(s, args, 0);
         break;
@@ -1175,6 +1344,10 @@ static const TCGTargetOpDef x86_op_defs[] = {
     { INDEX_op_ext8u_i32, { "r", "q"} },
     { INDEX_op_ext16u_i32, { "r", "r"} },
 
+    { INDEX_op_setcond_i32, { "q", "r", "ri" } },
+    { INDEX_op_movcond_i32, { "r", "r", "ri", "ri", "ri" } },
+    { INDEX_op_setcond2_i32, { "r", "r", "r", "ri", "ri" } },
+
 #if TARGET_LONG_BITS == 32
     { INDEX_op_qemu_ld8u, { "r", "L" } },
     { INDEX_op_qemu_ld8s, { "r", "L" } },
-- 
1.6.5.2