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tcg: Allow an operand to be matching or a constant

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This allows an output operand to match an input operand
only when the input operand needs a register.

Backports commit 17280ff4a5f264e01e55ae514ee6d3586f9577b2 from qemu
This commit is contained in:
Richard Henderson 2018-03-01 15:49:03 -05:00 committed by Lioncash
parent 3f38611159
commit b4b173615c
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GPG key ID: 4E3C3CC1031BA9C7
2 changed files with 50 additions and 35 deletions
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13
qemu/tcg/README
View file

@ -533,24 +533,29 @@ version. Aliases are specified in the input operands as for GCC.
The same register may be used for both an input and an output, even when
they are not explicitly aliased. If an op expands to multiple target
instructions then care must be taken to avoid clobbering input values.
GCC style "early clobber" outputs are not currently supported.
GCC style "early clobber" outputs are supported, with '&'.
A target can define specific register or constant constraints. If an
operation uses a constant input constraint which does not allow all
constants, it must also accept registers in order to have a fallback.
The constraint 'i' is defined generically to accept any constant.
The constraint 'r' is not defined generically, but is consistently
used by each backend to indicate all registers.
The movi_i32 and movi_i64 operations must accept any constants.
The mov_i32 and mov_i64 operations must accept any registers of the
same type.
The ld/st instructions must accept signed 32 bit constant offsets. It
can be implemented by reserving a specific register to compute the
address if the offset is too big.
The ld/st/sti instructions must accept signed 32 bit constant offsets.
This can be implemented by reserving a specific register in which to
compute the address if the offset is too big.
The ld/st instructions must accept any destination (ld) or source (st)
register.
The sti instruction may fail if it cannot store the given constant.
4.3) Function call assumptions
- The only supported types for parameters and return value are: 32 and

72
qemu/tcg/tcg.c
View file

@ -1301,37 +1301,46 @@ static void process_op_defs(TCGContext *s)
tcg_regset_clear(def->args_ct[i].u.regs);
def->args_ct[i].ct = 0;
if (ct_str[0] >= '0' && ct_str[0] <= '9') {
int oarg;
oarg = ct_str[0] - '0';
tcg_debug_assert(oarg < def->nb_oargs);
tcg_debug_assert(def->args_ct[oarg].ct & TCG_CT_REG);
/* TCG_CT_ALIAS is for the output arguments. The input
argument is tagged with TCG_CT_IALIAS. */
def->args_ct[i] = def->args_ct[oarg];
def->args_ct[oarg].ct = TCG_CT_ALIAS;
def->args_ct[oarg].alias_index = i;
def->args_ct[i].ct |= TCG_CT_IALIAS;
def->args_ct[i].alias_index = oarg;
} else {
for(;;) {
if (*ct_str == '\0')
break;
switch(*ct_str) {
case '&':
def->args_ct[i].ct |= TCG_CT_NEWREG;
ct_str++;
break;
case 'i':
def->args_ct[i].ct |= TCG_CT_CONST;
ct_str++;
break;
default:
ct_str = target_parse_constraint(&def->args_ct[i],
ct_str, type);
/* Typo in TCGTargetOpDef constraint. */
tcg_debug_assert(ct_str != NULL);
while (*ct_str != '\0') {
switch(*ct_str) {
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '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].ct & TCG_CT_REG);
/* TCG_CT_ALIAS is for the output arguments.
The input is tagged with TCG_CT_IALIAS. */
def->args_ct[i] = def->args_ct[oarg];
def->args_ct[oarg].ct |= TCG_CT_ALIAS;
def->args_ct[oarg].alias_index = i;
def->args_ct[i].ct |= TCG_CT_IALIAS;
def->args_ct[i].alias_index = oarg;
}
ct_str++;
break;
case '&':
def->args_ct[i].ct |= TCG_CT_NEWREG;
ct_str++;
break;
case 'i':
def->args_ct[i].ct |= TCG_CT_CONST;
ct_str++;
break;
default:
ct_str = target_parse_constraint(&def->args_ct[i],
ct_str, type);
/* Typo in TCGTargetOpDef constraint. */
tcg_debug_assert(ct_str != NULL);
}
}
}
@ -2356,7 +2365,8 @@ static void tcg_reg_alloc_op(TCGContext *s,
arg = args[i];
arg_ct = &def->args_ct[i];
ts = &s->temps[arg];
if (arg_ct->ct & TCG_CT_ALIAS) {
if ((arg_ct->ct & TCG_CT_ALIAS)
&& !const_args[arg_ct->alias_index]) {
reg = new_args[arg_ct->alias_index];
} else if (arg_ct->ct & TCG_CT_NEWREG) {
reg = tcg_reg_alloc(s, arg_ct->u.regs,