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tcg: Improve register allocation for matching constraints

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Try harder to honor the output_pref. When we're forced to allocate
a second register for the input, it does not need to use the input
constraint; that will be honored by the register we allocate for the
output and a move is already required.

Backports commit d62816f2db439b2dd761c674f0256f21d9dd2ed0 from qemu
This commit is contained in:
Richard Henderson 2019-01-05 06:57:15 -05:00 committed by Lioncash
parent 83a7de2566
commit 494d802781
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GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 24 additions and 12 deletions
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36
qemu/tcg/tcg.c
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@ -2749,6 +2749,8 @@ static void tcg_reg_alloc_op(TCGContext *s, const TCGOp *op)
/* satisfy input constraints */ /* satisfy input constraints */
for (k = 0; k < nb_iargs; k++) { for (k = 0; k < nb_iargs; k++) {
TCGRegSet i_preferred_regs, o_preferred_regs;
i = def->sorted_args[nb_oargs + k]; i = def->sorted_args[nb_oargs + k];
arg = op->args[i]; arg = op->args[i];
arg_ct = &def->args_ct[i]; arg_ct = &def->args_ct[i];
@ -2759,17 +2761,18 @@ static void tcg_reg_alloc_op(TCGContext *s, const TCGOp *op)
/* constant is OK for instruction */ /* constant is OK for instruction */
const_args[i] = 1; const_args[i] = 1;
new_args[i] = ts->val; new_args[i] = ts->val;
goto iarg_end; continue;
} }
temp_load(s, ts, arg_ct->u.regs, i_allocated_regs, 0); i_preferred_regs = o_preferred_regs = 0;
if (arg_ct->ct & TCG_CT_IALIAS) { if (arg_ct->ct & TCG_CT_IALIAS) {
o_preferred_regs = op->output_pref[arg_ct->alias_index];
if (ts->fixed_reg) { if (ts->fixed_reg) {
/* if fixed register, we must allocate a new register /* if fixed register, we must allocate a new register
if the alias is not the same register */ if the alias is not the same register */
if (arg != op->args[arg_ct->alias_index]) if (arg != op->args[arg_ct->alias_index]) {
goto allocate_in_reg; goto allocate_in_reg;
}
} else { } else {
/* if the input is aliased to an output and if it is /* if the input is aliased to an output and if it is
not dead after the instruction, we must allocate not dead after the instruction, we must allocate
@ -2777,33 +2780,42 @@ static void tcg_reg_alloc_op(TCGContext *s, const TCGOp *op)
if (!IS_DEAD_ARG(i)) { if (!IS_DEAD_ARG(i)) {
goto allocate_in_reg; goto allocate_in_reg;
} }
/* check if the current register has already been allocated /* check if the current register has already been allocated
for another input aliased to an output */ for another input aliased to an output */
int k2, i2; if (ts->val_type == TEMP_VAL_REG) {
for (k2 = 0 ; k2 < k ; k2++) { int k2, i2;
i2 = def->sorted_args[nb_oargs + k2]; reg = ts->reg;
if ((def->args_ct[i2].ct & TCG_CT_IALIAS) && for (k2 = 0 ; k2 < k ; k2++) {
(new_args[i2] == ts->reg)) { i2 = def->sorted_args[nb_oargs + k2];
goto allocate_in_reg; if ((def->args_ct[i2].ct & TCG_CT_IALIAS) &&
reg == new_args[i2]) {
goto allocate_in_reg;
}
} }
} }
i_preferred_regs = o_preferred_regs;
} }
} }
temp_load(s, ts, arg_ct->u.regs, i_allocated_regs, i_preferred_regs);
reg = ts->reg; reg = ts->reg;
if (tcg_regset_test_reg(arg_ct->u.regs, reg)) { if (tcg_regset_test_reg(arg_ct->u.regs, reg)) {
/* nothing to do : the constraint is satisfied */ /* nothing to do : the constraint is satisfied */
} else { } else {
allocate_in_reg: allocate_in_reg:
/* allocate a new register matching the constraint /* allocate a new register matching the constraint
and move the temporary register into it */ and move the temporary register into it */
temp_load(s, ts, s->tcg_target_available_regs[ts->type],
i_allocated_regs, 0);
reg = tcg_reg_alloc(s, arg_ct->u.regs, i_allocated_regs, reg = tcg_reg_alloc(s, arg_ct->u.regs, i_allocated_regs,
0, ts->indirect_base); o_preferred_regs, ts->indirect_base);
tcg_out_mov(s, ts->type, reg, ts->reg); tcg_out_mov(s, ts->type, reg, ts->reg);
} }
new_args[i] = reg; new_args[i] = reg;
const_args[i] = 0; const_args[i] = 0;
tcg_regset_set_reg(i_allocated_regs, reg); tcg_regset_set_reg(i_allocated_regs, reg);
iarg_end: ;
} }
/* mark dead temporaries and free the associated registers */ /* mark dead temporaries and free the associated registers */