参照元†
- rtx x
- machine_mode mem_mode
- rtx insn
- bool may_use_invariant
- bool for_costs
返り値†
/* Scan X and replace any eliminable registers (such as fp) with a
replacement (such as sp), plus an offset.
MEM_MODE is the mode of an enclosing MEM. We need this to know how
much to adjust a register for, e.g., PRE_DEC. Also, if we are inside a
MEM, we are allowed to replace a sum of a register and the constant zero
with the register, which we cannot do outside a MEM. In addition, we need
to record the fact that a register is referenced outside a MEM.
If INSN is an insn, it is the insn containing X. If we replace a REG
in a SET_DEST with an equivalent MEM and INSN is nonzero, write a
CLOBBER of the pseudo after INSN so find_equiv_regs will know that
the REG is being modified.
Alternatively, INSN may be a note (an EXPR_LIST or INSN_LIST).
That's used when we eliminate in expressions stored in notes.
This means, do not set ref_outside_mem even if the reference
is outside of MEMs.
If FOR_COSTS is true, we are being called before reload in order to
estimate the costs of keeping registers with an equivalence unallocated.
REG_EQUIV_MEM and REG_EQUIV_ADDRESS contain address that have had
replacements done assuming all offsets are at their initial values. If
they are not, or if REG_EQUIV_ADDRESS is nonzero for a pseudo we
encounter, return the actual location so that find_reloads will do
the proper thing. */
static rtx
eliminate_regs_1 (rtx x, machine_mode mem_mode, rtx insn,
bool may_use_invariant, bool for_costs)
{
enum rtx_code code = GET_CODE (x);
struct elim_table *ep;
int regno;
rtx new_rtx;
int i, j;
const char *fmt;
int copied = 0;
if (! current_function_decl)
return x;
switch (code)
{
CASE_CONST_ANY:
case CONST:
case SYMBOL_REF:
case CODE_LABEL:
case PC:
case CC0:
case ASM_INPUT:
case ADDR_VEC:
case ADDR_DIFF_VEC:
case RETURN:
return x;
case REG:
regno = REGNO (x);
/* First handle the case where we encounter a bare register that
is eliminable. Replace it with a PLUS. */
if (regno < FIRST_PSEUDO_REGISTER)
{
for (ep = reg_eliminate; ep < ®_eliminate[NUM_ELIMINABLE_REGS];
ep++)
if (ep->from_rtx == x && ep->can_eliminate)
return plus_constant (Pmode, ep->to_rtx, ep->previous_offset);
}
else if (reg_renumber && reg_renumber[regno] < 0
&& reg_equivs
&& reg_equiv_invariant (regno))
{
if (may_use_invariant || (insn && DEBUG_INSN_P (insn)))
return eliminate_regs_1 (copy_rtx (reg_equiv_invariant (regno)),
mem_mode, insn, true, for_costs);
/* There exists at least one use of REGNO that cannot be
eliminated. Prevent the defining insn from being deleted. */
reg_equiv_init (regno) = NULL;
if (!for_costs)
alter_reg (regno, -1, true);
}
return x;
/* You might think handling MINUS in a manner similar to PLUS is a
good idea. It is not. It has been tried multiple times and every
time the change has had to have been reverted.
Other parts of reload know a PLUS is special (gen_reload for example)
and require special code to handle code a reloaded PLUS operand.
Also consider backends where the flags register is clobbered by a
MINUS, but we can emit a PLUS that does not clobber flags (IA-32,
lea instruction comes to mind). If we try to reload a MINUS, we
may kill the flags register that was holding a useful value.
So, please before trying to handle MINUS, consider reload as a
whole instead of this little section as well as the backend issues. */
case PLUS:
/* If this is the sum of an eliminable register and a constant, rework
the sum. */
if (REG_P (XEXP (x, 0))
&& REGNO (XEXP (x, 0)) < FIRST_PSEUDO_REGISTER
&& CONSTANT_P (XEXP (x, 1)))
{
for (ep = reg_eliminate; ep < ®_eliminate[NUM_ELIMINABLE_REGS];
ep++)
if (ep->from_rtx == XEXP (x, 0) && ep->can_eliminate)
{
/* The only time we want to replace a PLUS with a REG (this
occurs when the constant operand of the PLUS is the negative
of the offset) is when we are inside a MEM. We won't want
to do so at other times because that would change the
structure of the insn in a way that reload can't handle.
We special-case the commonest situation in
eliminate_regs_in_insn, so just replace a PLUS with a
PLUS here, unless inside a MEM. */
rtx _t;
if (mem_mode != 0
&& CONST_INT_P (XEXP (x, 1))
&& known_eq (INTVAL (XEXP (x, 1)), -ep->previous_offset))
return ep->to_rtx;
else
return gen_rtx_PLUS (Pmode, ep->to_rtx,
plus_constant (Pmode, XEXP (x, 1),
ep->previous_offset));
}
}
/* If the register is not eliminable, we are done since the other
operand is a constant. */
return x;
}
/* If this is part of an address, we want to bring any constant to the
outermost PLUS. We will do this by doing register replacement in
our operands and seeing if a constant shows up in one of them.
Note that there is no risk of modifying the structure of the insn,
since we only get called for its operands, thus we are either
modifying the address inside a MEM, or something like an address
operand of a load-address insn. */
{
rtx new0 = eliminate_regs_1 (XEXP (x, 0), mem_mode, insn, true,
for_costs);
rtx new1 = eliminate_regs_1 (XEXP (x, 1), mem_mode, insn, true,
for_costs);
if (reg_renumber && (new0 != XEXP (x, 0) || new1 != XEXP (x, 1)))
{
/* If one side is a PLUS and the other side is a pseudo that
didn't get a hard register but has a reg_equiv_constant,
we must replace the constant here since it may no longer
be in the position of any operand. */
if (GET_CODE (new0) == PLUS && REG_P (new1)
&& REGNO (new1) >= FIRST_PSEUDO_REGISTER
&& reg_renumber[REGNO (new1)] < 0
&& reg_equivs
&& reg_equiv_constant (REGNO (new1)) != 0)
new1 = reg_equiv_constant (REGNO (new1));
else if (GET_CODE (new1) == PLUS && REG_P (new0)
&& REGNO (new0) >= FIRST_PSEUDO_REGISTER
&& reg_renumber[REGNO (new0)] < 0
&& reg_equiv_constant (REGNO (new0)) != 0)
new0 = reg_equiv_constant (REGNO (new0));
new_rtx = form_sum (GET_MODE (x), new0, new1);
/* As above, if we are not inside a MEM we do not want to
turn a PLUS into something else. We might try to do so here
for an addition of 0 if we aren't optimizing. */
if (! mem_mode && GET_CODE (new_rtx) != PLUS)
return gen_rtx_PLUS (GET_MODE (x), new_rtx, const0_rtx);
else
return new_rtx;
}
}
return x;
case MULT:
/* If this is the product of an eliminable register and a
constant, apply the distribute law and move the constant out
so that we have (plus (mult ..) ..). This is needed in order
to keep load-address insns valid. This case is pathological.
We ignore the possibility of overflow here. */
if (REG_P (XEXP (x, 0))
&& REGNO (XEXP (x, 0)) < FIRST_PSEUDO_REGISTER
&& CONST_INT_P (XEXP (x, 1)))
for (ep = reg_eliminate; ep < ®_eliminate[NUM_ELIMINABLE_REGS];
ep++)
if (ep->from_rtx == XEXP (x, 0) && ep->can_eliminate)
{
if (! mem_mode
/* Refs inside notes or in DEBUG_INSNs don't count for
this purpose. */
&& ! (insn != 0 && (GET_CODE (insn) == EXPR_LIST
|| GET_CODE (insn) == INSN_LIST
|| DEBUG_INSN_P (insn))))
ep->ref_outside_mem = 1;
return
plus_constant (Pmode,
gen_rtx_MULT (Pmode, ep->to_rtx, XEXP (x, 1)),
ep->previous_offset * INTVAL (XEXP (x, 1)));
}
/* fall through */
case CALL:
case COMPARE:
/* See comments before PLUS about handling MINUS. */
case MINUS:
case DIV: case UDIV:
case MOD: case UMOD:
case AND: case IOR: case XOR:
case ROTATERT: case ROTATE:
case ASHIFTRT: case LSHIFTRT: case ASHIFT:
case NE: case EQ:
case GE: case GT: case GEU: case GTU:
case LE: case LT: case LEU: case LTU:
{
rtx new0 = eliminate_regs_1 (XEXP (x, 0), mem_mode, insn, false,
for_costs);
rtx new1 = XEXP (x, 1)
? eliminate_regs_1 (XEXP (x, 1), mem_mode, insn, false,
for_costs) : 0;
if (new0 != XEXP (x, 0) || new1 != XEXP (x, 1))
return gen_rtx_fmt_ee (code, GET_MODE (x), new0, new1);
}
return x;
case EXPR_LIST:
/* If we have something in XEXP (x, 0), the usual case, eliminate it. */
if (XEXP (x, 0))
{
new_rtx = eliminate_regs_1 (XEXP (x, 0), mem_mode, insn, true,
for_costs);
if (new_rtx != XEXP (x, 0))
{
/* If this is a REG_DEAD note, it is not valid anymore.
Using the eliminated version could result in creating a
REG_DEAD note for the stack or frame pointer. */
if (REG_NOTE_KIND (x) == REG_DEAD)
return (XEXP (x, 1)
? eliminate_regs_1 (XEXP (x, 1), mem_mode, insn, true,
for_costs)
: NULL_RTX);
x = alloc_reg_note (REG_NOTE_KIND (x), new_rtx, XEXP (x, 1));
}
}
/* fall through */
case INSN_LIST:
case INT_LIST:
/* Now do eliminations in the rest of the chain. If this was
an EXPR_LIST, this might result in allocating more memory than is
strictly needed, but it simplifies the code. */
if (XEXP (x, 1))
{
new_rtx = eliminate_regs_1 (XEXP (x, 1), mem_mode, insn, true,
for_costs);
if (new_rtx != XEXP (x, 1))
return
gen_rtx_fmt_ee (GET_CODE (x), GET_MODE (x), XEXP (x, 0), new_rtx);
}
return x;
case PRE_INC:
case POST_INC:
case PRE_DEC:
case POST_DEC:
/* We do not support elimination of a register that is modified.
elimination_effects has already make sure that this does not
happen. */
return x;
case PRE_MODIFY:
case POST_MODIFY:
/* We do not support elimination of a register that is modified.
elimination_effects has already make sure that this does not
happen. The only remaining case we need to consider here is
that the increment value may be an eliminable register. */
if (GET_CODE (XEXP (x, 1)) == PLUS
&& XEXP (XEXP (x, 1), 0) == XEXP (x, 0))
{
rtx new_rtx = eliminate_regs_1 (XEXP (XEXP (x, 1), 1), mem_mode,
insn, true, for_costs);
if (new_rtx != XEXP (XEXP (x, 1), 1))
return gen_rtx_fmt_ee (code, GET_MODE (x), XEXP (x, 0),
gen_rtx_PLUS (GET_MODE (x),
XEXP (x, 0), new_rtx));
}
return x;
case STRICT_LOW_PART:
case NEG: case NOT:
case SIGN_EXTEND: case ZERO_EXTEND:
case TRUNCATE: case FLOAT_EXTEND: case FLOAT_TRUNCATE:
case FLOAT: case FIX:
case UNSIGNED_FIX: case UNSIGNED_FLOAT:
case ABS:
case SQRT:
case FFS:
case CLZ:
case CTZ:
case POPCOUNT:
case PARITY:
case BSWAP:
new_rtx = eliminate_regs_1 (XEXP (x, 0), mem_mode, insn, false,
for_costs);
if (new_rtx != XEXP (x, 0))
return gen_rtx_fmt_e (code, GET_MODE (x), new_rtx);
return x;
case SUBREG:
/* Similar to above processing, but preserve SUBREG_BYTE.
Convert (subreg (mem)) to (mem) if not paradoxical.
Also, if we have a non-paradoxical (subreg (pseudo)) and the
pseudo didn't get a hard reg, we must replace this with the
eliminated version of the memory location because push_reload
may do the replacement in certain circumstances. */
if (REG_P (SUBREG_REG (x))
&& !paradoxical_subreg_p (x)
&& reg_equivs
&& reg_equiv_memory_loc (REGNO (SUBREG_REG (x))) != 0)
{
new_rtx = SUBREG_REG (x);
}
else
new_rtx = eliminate_regs_1 (SUBREG_REG (x), mem_mode, insn, false, for_costs);
if (new_rtx != SUBREG_REG (x))
{
poly_int64 x_size = GET_MODE_SIZE (GET_MODE (x));
poly_int64 new_size = GET_MODE_SIZE (GET_MODE (new_rtx));
if (MEM_P (new_rtx)
&& ((partial_subreg_p (GET_MODE (x), GET_MODE (new_rtx))
/* On RISC machines, combine can create rtl of the form
(set (subreg:m1 (reg:m2 R) 0) ...)
where m1 < m2, and expects something interesting to
happen to the entire word. Moreover, it will use the
(reg:m2 R) later, expecting all bits to be preserved.
So if the number of words is the same, preserve the
subreg so that push_reload can see it. */
&& !(WORD_REGISTER_OPERATIONS
&& known_equal_after_align_down (x_size - 1,
new_size - 1,
UNITS_PER_WORD)))
|| known_eq (x_size, new_size))
)
return adjust_address_nv (new_rtx, GET_MODE (x), SUBREG_BYTE (x));
else if (insn && GET_CODE (insn) == DEBUG_INSN)
return gen_rtx_raw_SUBREG (GET_MODE (x), new_rtx, SUBREG_BYTE (x));
else
return gen_rtx_SUBREG (GET_MODE (x), new_rtx, SUBREG_BYTE (x));
}
return x;
case MEM:
/* Our only special processing is to pass the mode of the MEM to our
recursive call and copy the flags. While we are here, handle this
case more efficiently. */
new_rtx = eliminate_regs_1 (XEXP (x, 0), GET_MODE (x), insn, true,
for_costs);
if (for_costs
&& memory_address_p (GET_MODE (x), XEXP (x, 0))
&& !memory_address_p (GET_MODE (x), new_rtx))
note_reg_elim_costly (XEXP (x, 0), insn);
return replace_equiv_address_nv (x, new_rtx);
case USE:
/* Handle insn_list USE that a call to a pure function may generate. */
new_rtx = eliminate_regs_1 (XEXP (x, 0), VOIDmode, insn, false,
for_costs);
if (new_rtx != XEXP (x, 0))
return gen_rtx_USE (GET_MODE (x), new_rtx);
return x;
case CLOBBER:
case ASM_OPERANDS:
gcc_assert (insn && DEBUG_INSN_P (insn));
break;
case SET:
gcc_unreachable ();
default:
break;
}
/* Process each of our operands recursively. If any have changed, make a
copy of the rtx. */
fmt = GET_RTX_FORMAT (code);
for (i = 0; i < GET_RTX_LENGTH (code); i++, fmt++)
{
if (*fmt == 'e')
{
new_rtx = eliminate_regs_1 (XEXP (x, i), mem_mode, insn, false,
for_costs);
if (new_rtx != XEXP (x, i) && ! copied)
{
x = shallow_copy_rtx (x);
copied = 1;
}
XEXP (x, i) = new_rtx;
}
else if (*fmt == 'E')
{
int copied_vec = 0;
for (j = 0; j < XVECLEN (x, i); j++)
{
new_rtx = eliminate_regs_1 (XVECEXP (x, i, j), mem_mode, insn, false,
for_costs);
if (new_rtx != XVECEXP (x, i, j) && ! copied_vec)
{
rtvec new_v = gen_rtvec_v (XVECLEN (x, i),
XVEC (x, i)->elem);
if (! copied)
{
x = shallow_copy_rtx (x);
copied = 1;
}
XVEC (x, i) = new_v;
copied_vec = 1;
}
XVECEXP (x, i, j) = new_rtx;
}
}
}
return x;
}
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