diff --git a/include/tcg/tcg.h b/include/tcg/tcg.h
index d84bae6e3f..5c2254ce9f 100644
--- a/include/tcg/tcg.h
+++ b/include/tcg/tcg.h
@@ -951,6 +951,8 @@ typedef struct TCGArgConstraint {
     unsigned ct : 16;
     unsigned alias_index : 4;
     unsigned sort_index : 4;
+    unsigned pair_index : 4;
+    unsigned pair : 2;  /* 0: none, 1: first, 2: second, 3: second alias */
     bool oalias : 1;
     bool ialias : 1;
     bool newreg : 1;
diff --git a/tcg/tcg.c b/tcg/tcg.c
index 660d5eb098..e9ff3c92e5 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -1985,15 +1985,32 @@ static void tcg_dump_ops(TCGContext *s, FILE *f, bool have_prefs)
 static int get_constraint_priority(const TCGOpDef *def, int k)
 {
     const TCGArgConstraint *arg_ct = &def->args_ct[k];
-    int n;
+    int n = ctpop64(arg_ct->regs);
 
-    if (arg_ct->oalias) {
-        /* an alias is equivalent to a single register */
-        n = 1;
-    } else {
-        n = ctpop64(arg_ct->regs);
+    /*
+     * Sort constraints of a single register first, which includes output
+     * aliases (which must exactly match the input already allocated).
+     */
+    if (n == 1 || arg_ct->oalias) {
+        return INT_MAX;
     }
-    return TCG_TARGET_NB_REGS - n + 1;
+
+    /*
+     * Sort register pairs next, first then second immediately after.
+     * Arbitrarily sort multiple pairs by the index of the first reg;
+     * there shouldn't be many pairs.
+     */
+    switch (arg_ct->pair) {
+    case 1:
+    case 3:
+        return (k + 1) * 2;
+    case 2:
+        return (arg_ct->pair_index + 1) * 2 - 1;
+    }
+
+    /* Finally, sort by decreasing register count. */
+    assert(n > 1);
+    return -n;
 }
 
 /* sort from highest priority to lowest */
@@ -2028,7 +2045,8 @@ static void process_op_defs(TCGContext *s)
     for (op = 0; op < NB_OPS; op++) {
         TCGOpDef *def = &tcg_op_defs[op];
         const TCGTargetOpDef *tdefs;
-        int i, nb_args;
+        bool saw_alias_pair = false;
+        int i, o, i2, o2, nb_args;
 
         if (def->flags & TCG_OPF_NOT_PRESENT) {
             continue;
@@ -2050,58 +2068,175 @@ static void process_op_defs(TCGContext *s)
 
         for (i = 0; i < nb_args; i++) {
             const char *ct_str = tdefs->args_ct_str[i];
+            bool input_p = i >= def->nb_oargs;
+
             /* Incomplete TCGTargetOpDef entry. */
             tcg_debug_assert(ct_str != NULL);
 
-            while (*ct_str != '\0') {
-                switch(*ct_str) {
-                case '0' ... '9':
-                    {
-                        int oarg = *ct_str - '0';
-                        tcg_debug_assert(ct_str == tdefs->args_ct_str[i]);
-                        tcg_debug_assert(oarg < def->nb_oargs);
-                        tcg_debug_assert(def->args_ct[oarg].regs != 0);
-                        def->args_ct[i] = def->args_ct[oarg];
-                        /* The output sets oalias.  */
-                        def->args_ct[oarg].oalias = true;
-                        def->args_ct[oarg].alias_index = i;
-                        /* The input sets ialias. */
-                        def->args_ct[i].ialias = true;
-                        def->args_ct[i].alias_index = oarg;
-                    }
-                    ct_str++;
-                    break;
-                case '&':
-                    def->args_ct[i].newreg = true;
-                    ct_str++;
-                    break;
+            switch (*ct_str) {
+            case '0' ... '9':
+                o = *ct_str - '0';
+                tcg_debug_assert(input_p);
+                tcg_debug_assert(o < def->nb_oargs);
+                tcg_debug_assert(def->args_ct[o].regs != 0);
+                tcg_debug_assert(!def->args_ct[o].oalias);
+                def->args_ct[i] = def->args_ct[o];
+                /* The output sets oalias.  */
+                def->args_ct[o].oalias = 1;
+                def->args_ct[o].alias_index = i;
+                /* The input sets ialias. */
+                def->args_ct[i].ialias = 1;
+                def->args_ct[i].alias_index = o;
+                if (def->args_ct[i].pair) {
+                    saw_alias_pair = true;
+                }
+                tcg_debug_assert(ct_str[1] == '\0');
+                continue;
+
+            case '&':
+                tcg_debug_assert(!input_p);
+                def->args_ct[i].newreg = true;
+                ct_str++;
+                break;
+
+            case 'p': /* plus */
+                /* Allocate to the register after the previous. */
+                tcg_debug_assert(i > (input_p ? def->nb_oargs : 0));
+                o = i - 1;
+                tcg_debug_assert(!def->args_ct[o].pair);
+                tcg_debug_assert(!def->args_ct[o].ct);
+                def->args_ct[i] = (TCGArgConstraint){
+                    .pair = 2,
+                    .pair_index = o,
+                    .regs = def->args_ct[o].regs << 1,
+                };
+                def->args_ct[o].pair = 1;
+                def->args_ct[o].pair_index = i;
+                tcg_debug_assert(ct_str[1] == '\0');
+                continue;
+
+            case 'm': /* minus */
+                /* Allocate to the register before the previous. */
+                tcg_debug_assert(i > (input_p ? def->nb_oargs : 0));
+                o = i - 1;
+                tcg_debug_assert(!def->args_ct[o].pair);
+                tcg_debug_assert(!def->args_ct[o].ct);
+                def->args_ct[i] = (TCGArgConstraint){
+                    .pair = 1,
+                    .pair_index = o,
+                    .regs = def->args_ct[o].regs >> 1,
+                };
+                def->args_ct[o].pair = 2;
+                def->args_ct[o].pair_index = i;
+                tcg_debug_assert(ct_str[1] == '\0');
+                continue;
+            }
+
+            do {
+                switch (*ct_str) {
                 case 'i':
                     def->args_ct[i].ct |= TCG_CT_CONST;
-                    ct_str++;
                     break;
 
                 /* Include all of the target-specific constraints. */
 
 #undef CONST
 #define CONST(CASE, MASK) \
-    case CASE: def->args_ct[i].ct |= MASK; ct_str++; break;
+    case CASE: def->args_ct[i].ct |= MASK; break;
 #define REGS(CASE, MASK) \
-    case CASE: def->args_ct[i].regs |= MASK; ct_str++; break;
+    case CASE: def->args_ct[i].regs |= MASK; break;
 
 #include "tcg-target-con-str.h"
 
 #undef REGS
 #undef CONST
                 default:
+                case '0' ... '9':
+                case '&':
+                case 'p':
+                case 'm':
                     /* Typo in TCGTargetOpDef constraint. */
                     g_assert_not_reached();
                 }
-            }
+            } while (*++ct_str != '\0');
         }
 
         /* TCGTargetOpDef entry with too much information? */
         tcg_debug_assert(i == TCG_MAX_OP_ARGS || tdefs->args_ct_str[i] == NULL);
 
+        /*
+         * Fix up output pairs that are aliased with inputs.
+         * When we created the alias, we copied pair from the output.
+         * There are three cases:
+         *    (1a) Pairs of inputs alias pairs of outputs.
+         *    (1b) One input aliases the first of a pair of outputs.
+         *    (2)  One input aliases the second of a pair of outputs.
+         *
+         * Case 1a is handled by making sure that the pair_index'es are
+         * properly updated so that they appear the same as a pair of inputs.
+         *
+         * Case 1b is handled by setting the pair_index of the input to
+         * itself, simply so it doesn't point to an unrelated argument.
+         * Since we don't encounter the "second" during the input allocation
+         * phase, nothing happens with the second half of the input pair.
+         *
+         * Case 2 is handled by setting the second input to pair=3, the
+         * first output to pair=3, and the pair_index'es to match.
+         */
+        if (saw_alias_pair) {
+            for (i = def->nb_oargs; i < nb_args; i++) {
+                /*
+                 * Since [0-9pm] must be alone in the constraint string,
+                 * the only way they can both be set is if the pair comes
+                 * from the output alias.
+                 */
+                if (!def->args_ct[i].ialias) {
+                    continue;
+                }
+                switch (def->args_ct[i].pair) {
+                case 0:
+                    break;
+                case 1:
+                    o = def->args_ct[i].alias_index;
+                    o2 = def->args_ct[o].pair_index;
+                    tcg_debug_assert(def->args_ct[o].pair == 1);
+                    tcg_debug_assert(def->args_ct[o2].pair == 2);
+                    if (def->args_ct[o2].oalias) {
+                        /* Case 1a */
+                        i2 = def->args_ct[o2].alias_index;
+                        tcg_debug_assert(def->args_ct[i2].pair == 2);
+                        def->args_ct[i2].pair_index = i;
+                        def->args_ct[i].pair_index = i2;
+                    } else {
+                        /* Case 1b */
+                        def->args_ct[i].pair_index = i;
+                    }
+                    break;
+                case 2:
+                    o = def->args_ct[i].alias_index;
+                    o2 = def->args_ct[o].pair_index;
+                    tcg_debug_assert(def->args_ct[o].pair == 2);
+                    tcg_debug_assert(def->args_ct[o2].pair == 1);
+                    if (def->args_ct[o2].oalias) {
+                        /* Case 1a */
+                        i2 = def->args_ct[o2].alias_index;
+                        tcg_debug_assert(def->args_ct[i2].pair == 1);
+                        def->args_ct[i2].pair_index = i;
+                        def->args_ct[i].pair_index = i2;
+                    } else {
+                        /* Case 2 */
+                        def->args_ct[i].pair = 3;
+                        def->args_ct[o2].pair = 3;
+                        def->args_ct[i].pair_index = o2;
+                        def->args_ct[o2].pair_index = i;
+                    }
+                    break;
+                default:
+                    g_assert_not_reached();
+                }
+            }
+        }
+
         /* sort the constraints (XXX: this is just an heuristic) */
         sort_constraints(def, 0, def->nb_oargs);
         sort_constraints(def, def->nb_oargs, def->nb_iargs);
@@ -3197,6 +3332,52 @@ static TCGReg tcg_reg_alloc(TCGContext *s, TCGRegSet required_regs,
     tcg_abort();
 }
 
+static TCGReg tcg_reg_alloc_pair(TCGContext *s, TCGRegSet required_regs,
+                                 TCGRegSet allocated_regs,
+                                 TCGRegSet preferred_regs, bool rev)
+{
+    int i, j, k, fmin, n = ARRAY_SIZE(tcg_target_reg_alloc_order);
+    TCGRegSet reg_ct[2];
+    const int *order;
+
+    /* Ensure that if I is not in allocated_regs, I+1 is not either. */
+    reg_ct[1] = required_regs & ~(allocated_regs | (allocated_regs >> 1));
+    tcg_debug_assert(reg_ct[1] != 0);
+    reg_ct[0] = reg_ct[1] & preferred_regs;
+
+    order = rev ? indirect_reg_alloc_order : tcg_target_reg_alloc_order;
+
+    /*
+     * Skip the preferred_regs option if it cannot be satisfied,
+     * or if the preference made no difference.
+     */
+    k = reg_ct[0] == 0 || reg_ct[0] == reg_ct[1];
+
+    /*
+     * Minimize the number of flushes by looking for 2 free registers first,
+     * then a single flush, then two flushes.
+     */
+    for (fmin = 2; fmin >= 0; fmin--) {
+        for (j = k; j < 2; j++) {
+            TCGRegSet set = reg_ct[j];
+
+            for (i = 0; i < n; i++) {
+                TCGReg reg = order[i];
+
+                if (tcg_regset_test_reg(set, reg)) {
+                    int f = !s->reg_to_temp[reg] + !s->reg_to_temp[reg + 1];
+                    if (f >= fmin) {
+                        tcg_reg_free(s, reg, allocated_regs);
+                        tcg_reg_free(s, reg + 1, allocated_regs);
+                        return reg;
+                    }
+                }
+            }
+        }
+    }
+    tcg_abort();
+}
+
 /* Make sure the temporary is in a register.  If needed, allocate the register
    from DESIRED while avoiding ALLOCATED.  */
 static void temp_load(TCGContext *s, TCGTemp *ts, TCGRegSet desired_regs,
@@ -3606,8 +3787,10 @@ static void tcg_reg_alloc_op(TCGContext *s, const TCGOp *op)
 
     /* satisfy input constraints */ 
     for (k = 0; k < nb_iargs; k++) {
-        TCGRegSet i_preferred_regs;
-        bool allocate_new_reg;
+        TCGRegSet i_preferred_regs, i_required_regs;
+        bool allocate_new_reg, copyto_new_reg;
+        TCGTemp *ts2;
+        int i1, i2;
 
         i = def->args_ct[nb_oargs + k].sort_index;
         arg = op->args[i];
@@ -3624,43 +3807,142 @@ static void tcg_reg_alloc_op(TCGContext *s, const TCGOp *op)
 
         reg = ts->reg;
         i_preferred_regs = 0;
+        i_required_regs = arg_ct->regs;
         allocate_new_reg = false;
+        copyto_new_reg = false;
 
-        if (arg_ct->ialias) {
+        switch (arg_ct->pair) {
+        case 0: /* not paired */
+            if (arg_ct->ialias) {
+                i_preferred_regs = op->output_pref[arg_ct->alias_index];
+
+                /*
+                 * If the input is readonly, then it cannot also be an
+                 * output and aliased to itself.  If the input is not
+                 * dead after the instruction, we must allocate a new
+                 * register and move it.
+                 */
+                if (temp_readonly(ts) || !IS_DEAD_ARG(i)) {
+                    allocate_new_reg = true;
+                } else if (ts->val_type == TEMP_VAL_REG) {
+                    /*
+                     * Check if the current register has already been
+                     * allocated for another input.
+                     */
+                    allocate_new_reg =
+                        tcg_regset_test_reg(i_allocated_regs, reg);
+                }
+            }
+            if (!allocate_new_reg) {
+                temp_load(s, ts, i_required_regs, i_allocated_regs,
+                          i_preferred_regs);
+                reg = ts->reg;
+                allocate_new_reg = !tcg_regset_test_reg(i_required_regs, reg);
+            }
+            if (allocate_new_reg) {
+                /*
+                 * Allocate a new register matching the constraint
+                 * and move the temporary register into it.
+                 */
+                temp_load(s, ts, tcg_target_available_regs[ts->type],
+                          i_allocated_regs, 0);
+                reg = tcg_reg_alloc(s, i_required_regs, i_allocated_regs,
+                                    i_preferred_regs, ts->indirect_base);
+                copyto_new_reg = true;
+            }
+            break;
+
+        case 1:
+            /* First of an input pair; if i1 == i2, the second is an output. */
+            i1 = i;
+            i2 = arg_ct->pair_index;
+
+            /*
+             * It is easier to default to allocating a new pair
+             * and to identify a few cases where it's not required.
+             */
+            allocate_new_reg = true;
+            ts2 = i1 != i2 ? arg_temp(op->args[i2]) : NULL;
+
+            if (arg_ct->ialias) {
+                i_preferred_regs = op->output_pref[arg_ct->alias_index];
+                if (IS_DEAD_ARG(i1) &&
+                    IS_DEAD_ARG(i2) &&
+                    !temp_readonly(ts) &&
+                    ts->val_type == TEMP_VAL_REG &&
+                    ts->reg < TCG_TARGET_NB_REGS - 1 &&
+                    tcg_regset_test_reg(i_required_regs, reg) &&
+                    !tcg_regset_test_reg(i_allocated_regs, reg) &&
+                    !tcg_regset_test_reg(i_allocated_regs, reg + 1) &&
+                    (ts2
+                     ? !temp_readonly(ts2) &&
+                       ts2->val_type == TEMP_VAL_REG &&
+                       ts2->reg == reg + 1
+                     : s->reg_to_temp[reg + 1] == NULL)) {
+                    allocate_new_reg = false;
+                }
+            } else {
+                /* Without aliasing, the pair must also be an input. */
+                tcg_debug_assert(ts2);
+                if (ts->val_type == TEMP_VAL_REG &&
+                    ts2->val_type == TEMP_VAL_REG &&
+                    ts2->reg == reg + 1 &&
+                    tcg_regset_test_reg(i_required_regs, reg)) {
+                    allocate_new_reg = false;
+                }
+            }
+            if (allocate_new_reg) {
+                reg = tcg_reg_alloc_pair(s, i_required_regs, i_allocated_regs,
+                                         0, ts->indirect_base);
+                if (ts->val_type != TEMP_VAL_REG) {
+                    temp_load(s, ts, (TCGRegSet)1 << reg, i_allocated_regs, 0);
+                } else {
+                    copyto_new_reg = true;
+                }
+            }
+            break;
+
+        case 2: /* pair second */
+            reg = new_args[arg_ct->pair_index] + 1;
+            i_required_regs = (TCGRegSet)1 << reg;
+            temp_load(s, ts, i_required_regs, i_allocated_regs, 0);
+            allocate_new_reg = ts->reg != reg;
+            break;
+
+        case 3: /* ialias with second output, no first input */
+            tcg_debug_assert(arg_ct->ialias);
             i_preferred_regs = op->output_pref[arg_ct->alias_index];
 
-            /*
-             * If the input is readonly, then it cannot also be an
-             * output and aliased to itself.  If the input is not
-             * dead after the instruction, we must allocate a new
-             * register and move it.
-             */
-            if (temp_readonly(ts) || !IS_DEAD_ARG(i)) {
-                allocate_new_reg = true;
-            } else if (ts->val_type == TEMP_VAL_REG) {
-                /*
-                 * Check if the current register has already been
-                 * allocated for another input.
-                 */
-                allocate_new_reg = tcg_regset_test_reg(i_allocated_regs, reg);
+            allocate_new_reg = true;
+            if (IS_DEAD_ARG(i) &&
+                ts->val_type == TEMP_VAL_REG &&
+                reg > 0 &&
+                !s->reg_to_temp[reg - 1] &&
+                tcg_regset_test_reg(i_required_regs, reg) &&
+                !tcg_regset_test_reg(i_allocated_regs, reg) &&
+                !tcg_regset_test_reg(i_allocated_regs, reg - 1)) {
+                tcg_regset_set_reg(i_allocated_regs, reg - 1);
+                allocate_new_reg = false;
             }
+            if (allocate_new_reg) {
+                reg = tcg_reg_alloc_pair(s, i_required_regs >> 1,
+                                         i_allocated_regs, 0,
+                                         ts->indirect_base);
+                tcg_regset_set_reg(i_allocated_regs, reg);
+                reg += 1;
+                if (ts->val_type != TEMP_VAL_REG) {
+                    temp_load(s, ts, (TCGRegSet)1 << reg, i_allocated_regs, 0);
+                } else {
+                    copyto_new_reg = true;
+                }
+            }
+            break;
+
+        default:
+            g_assert_not_reached();
         }
 
-        if (!allocate_new_reg) {
-            temp_load(s, ts, arg_ct->regs, i_allocated_regs, i_preferred_regs);
-            reg = ts->reg;
-            allocate_new_reg = !tcg_regset_test_reg(arg_ct->regs, reg);
-        }
-
-        if (allocate_new_reg) {
-            /*
-             * Allocate a new register matching the constraint
-             * and move the temporary register into it.
-             */
-            temp_load(s, ts, tcg_target_available_regs[ts->type],
-                      i_allocated_regs, 0);
-            reg = tcg_reg_alloc(s, arg_ct->regs, i_allocated_regs,
-                                i_preferred_regs, ts->indirect_base);
+        if (copyto_new_reg) {
             if (!tcg_out_mov(s, ts->type, reg, ts->reg)) {
                 /*
                  * Cross register class move not supported.  Sync the
@@ -3675,7 +3957,7 @@ static void tcg_reg_alloc_op(TCGContext *s, const TCGOp *op)
         const_args[i] = 0;
         tcg_regset_set_reg(i_allocated_regs, reg);
     }
-    
+
     /* mark dead temporaries and free the associated registers */
     for (i = nb_oargs; i < nb_oargs + nb_iargs; i++) {
         if (IS_DEAD_ARG(i)) {
@@ -3703,7 +3985,7 @@ static void tcg_reg_alloc_op(TCGContext *s, const TCGOp *op)
         }
         
         /* satisfy the output constraints */
-        for(k = 0; k < nb_oargs; k++) {
+        for (k = 0; k < nb_oargs; k++) {
             i = def->args_ct[k].sort_index;
             arg = op->args[i];
             arg_ct = &def->args_ct[i];
@@ -3712,15 +3994,46 @@ static void tcg_reg_alloc_op(TCGContext *s, const TCGOp *op)
             /* ENV should not be modified.  */
             tcg_debug_assert(!temp_readonly(ts));
 
-            if (arg_ct->oalias && !const_args[arg_ct->alias_index]) {
-                reg = new_args[arg_ct->alias_index];
-            } else if (arg_ct->newreg) {
-                reg = tcg_reg_alloc(s, arg_ct->regs,
-                                    i_allocated_regs | o_allocated_regs,
-                                    op->output_pref[k], ts->indirect_base);
-            } else {
-                reg = tcg_reg_alloc(s, arg_ct->regs, o_allocated_regs,
-                                    op->output_pref[k], ts->indirect_base);
+            switch (arg_ct->pair) {
+            case 0: /* not paired */
+                if (arg_ct->oalias && !const_args[arg_ct->alias_index]) {
+                    reg = new_args[arg_ct->alias_index];
+                } else if (arg_ct->newreg) {
+                    reg = tcg_reg_alloc(s, arg_ct->regs,
+                                        i_allocated_regs | o_allocated_regs,
+                                        op->output_pref[k], ts->indirect_base);
+                } else {
+                    reg = tcg_reg_alloc(s, arg_ct->regs, o_allocated_regs,
+                                        op->output_pref[k], ts->indirect_base);
+                }
+                break;
+
+            case 1: /* first of pair */
+                tcg_debug_assert(!arg_ct->newreg);
+                if (arg_ct->oalias) {
+                    reg = new_args[arg_ct->alias_index];
+                    break;
+                }
+                reg = tcg_reg_alloc_pair(s, arg_ct->regs, o_allocated_regs,
+                                         op->output_pref[k], ts->indirect_base);
+                break;
+
+            case 2: /* second of pair */
+                tcg_debug_assert(!arg_ct->newreg);
+                if (arg_ct->oalias) {
+                    reg = new_args[arg_ct->alias_index];
+                } else {
+                    reg = new_args[arg_ct->pair_index] + 1;
+                }
+                break;
+
+            case 3: /* first of pair, aliasing with a second input */
+                tcg_debug_assert(!arg_ct->newreg);
+                reg = new_args[arg_ct->pair_index] - 1;
+                break;
+
+            default:
+                g_assert_not_reached();
             }
             tcg_regset_set_reg(o_allocated_regs, reg);
             if (ts->val_type == TEMP_VAL_REG) {
@@ -3728,12 +4041,12 @@ static void tcg_reg_alloc_op(TCGContext *s, const TCGOp *op)
             }
             ts->val_type = TEMP_VAL_REG;
             ts->reg = reg;
+            s->reg_to_temp[reg] = ts;
             /*
              * Temp value is modified, so the value kept in memory is
              * potentially not the same.
              */
             ts->mem_coherent = 0;
-            s->reg_to_temp[reg] = ts;
             new_args[i] = reg;
         }
     }
