OpenE2K/gcc
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

re PR rtl-optimization/17236 (inefficient code for long long multiply on x86)

Browse Source 
PR rtl-optimization/17236
	* optabs.c (expand_doubleword_mult): New helper function split out
	from expand_binop.  Permute the order in which instructions are
	emitted to minimize the number of simultaneously live registers.
	(expand_binop): Call expand_doubleword_mult to synthesize a double
	word multiplication.

From-SVN: r96441
This commit is contained in:
Roger Sayle 2005-03-14 18:24:15 +00:00 committed by Roger Sayle
parent a6ee1a1532
commit f927760bad
2 changed files with 197 additions and 172 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
gcc/ChangeLog
View File

@ -1,3 +1,12 @@
2005-03-14 Roger Sayle <roger@eyesopen.com>
PR rtl-optimization/17236
* optabs.c (expand_doubleword_mult): New helper function split out
from expand_binop. Permute the order in which instructions are
emitted to minimize the number of simultaneously live registers.
(expand_binop): Call expand_doubleword_mult to synthesize a double
word multiplication.
2005-03-14 Kazu Hirata <kazu@cs.umass.edu>
* basic-block.h: Update the prototypes of cached_make_edge and

360
gcc/optabs.c
View File

@ -756,6 +756,168 @@ expand_doubleword_shift (enum machine_mode op1_mode, optab binoptab,
return true;
}
/* Subroutine of expand_binop. Perform a double word multiplication of
operands OP0 and OP1 both of mode MODE, which is exactly twice as wide
as the target's word_mode. This function return NULL_RTX if anything
goes wrong, in which case it may have already emitted instructions
which need to be deleted.
If we want to multiply two two-word values and have normal and widening
multiplies of single-word values, we can do this with three smaller
multiplications. Note that we do not make a REG_NO_CONFLICT block here
because we are not operating on one word at a time.
The multiplication proceeds as follows:
_______________________
[__op0_high_|__op0_low__]
_______________________
* [__op1_high_|__op1_low__]
_______________________________________________
_______________________
(1) [__op0_low__*__op1_low__]
_______________________
(2a) [__op0_low__*__op1_high_]
_______________________
(2b) [__op0_high_*__op1_low__]
_______________________
(3) [__op0_high_*__op1_high_]
This gives a 4-word result. Since we are only interested in the
lower 2 words, partial result (3) and the upper words of (2a) and
(2b) don't need to be calculated. Hence (2a) and (2b) can be
calculated using non-widening multiplication.
(1), however, needs to be calculated with an unsigned widening
multiplication. If this operation is not directly supported we
try using a signed widening multiplication and adjust the result.
This adjustment works as follows:
If both operands are positive then no adjustment is needed.
If the operands have different signs, for example op0_low < 0 and
op1_low >= 0, the instruction treats the most significant bit of
op0_low as a sign bit instead of a bit with significance
2**(BITS_PER_WORD-1), i.e. the instruction multiplies op1_low
with 2**BITS_PER_WORD - op0_low, and two's complements the
result. Conclusion: We need to add op1_low * 2**BITS_PER_WORD to
the result.
Similarly, if both operands are negative, we need to add
(op0_low + op1_low) * 2**BITS_PER_WORD.
We use a trick to adjust quickly. We logically shift op0_low right
(op1_low) BITS_PER_WORD-1 steps to get 0 or 1, and add this to
op0_high (op1_high) before it is used to calculate 2b (2a). If no
logical shift exists, we do an arithmetic right shift and subtract
the 0 or -1. */
static rtx
expand_doubleword_mult (enum machine_mode mode, rtx op0, rtx op1, rtx target,
bool umulp, enum optab_methods methods)
{
int low = (WORDS_BIG_ENDIAN ? 1 : 0);
int high = (WORDS_BIG_ENDIAN ? 0 : 1);
rtx wordm1 = umulp ? NULL_RTX : GEN_INT (BITS_PER_WORD - 1);
rtx product, adjust, product_high, temp;
rtx op0_high = operand_subword_force (op0, high, mode);
rtx op0_low = operand_subword_force (op0, low, mode);
rtx op1_high = operand_subword_force (op1, high, mode);
rtx op1_low = operand_subword_force (op1, low, mode);
/* If we're using an unsigned multiply to directly compute the product
of the low-order words of the operands and perform any required
adjustments of the operands, we begin by trying two more multiplications
and then computing the appropriate sum.
We have checked above that the required addition is provided.
Full-word addition will normally always succeed, especially if
it is provided at all, so we don't worry about its failure. The
multiplication may well fail, however, so we do handle that. */
if (!umulp)
{
/* ??? This could be done with emit_store_flag where available. */
temp = expand_binop (word_mode, lshr_optab, op0_low, wordm1,
NULL_RTX, 1, methods);
if (temp)
op0_high = expand_binop (word_mode, add_optab, op0_high, temp,
op0_high, 0, OPTAB_DIRECT);
else
{
temp = expand_binop (word_mode, ashr_optab, op0_low, wordm1,
NULL_RTX, 0, methods);
if (!temp)
return NULL_RTX;
op0_high = expand_binop (word_mode, sub_optab, op0_high, temp,
op0_high, 0, OPTAB_DIRECT);
}
if (!op0_high)
return NULL_RTX;
}
adjust = expand_binop (word_mode, smul_optab, op0_high, op1_low,
NULL_RTX, 0, OPTAB_DIRECT);
if (!adjust)
return NULL_RTX;
/* OP0_HIGH should now be dead. */
if (!umulp)
{
/* ??? This could be done with emit_store_flag where available. */
temp = expand_binop (word_mode, lshr_optab, op1_low, wordm1,
NULL_RTX, 1, methods);
if (temp)
op1_high = expand_binop (word_mode, add_optab, op1_high, temp,
op1_high, 0, OPTAB_DIRECT);
else
{
temp = expand_binop (word_mode, ashr_optab, op1_low, wordm1,
NULL_RTX, 0, methods);
if (!temp)
return NULL_RTX;
op1_high = expand_binop (word_mode, sub_optab, op1_high, temp,
op1_high, 0, OPTAB_DIRECT);
}
if (!op1_high)
return NULL_RTX;
}
temp = expand_binop (word_mode, smul_optab, op1_high, op0_low,
NULL_RTX, 0, OPTAB_DIRECT);
if (!temp)
return NULL_RTX;
/* OP1_HIGH should now be dead. */
adjust = expand_binop (word_mode, add_optab, adjust, temp,
adjust, 0, OPTAB_DIRECT);
if (target && !REG_P (target))
target = NULL_RTX;
if (umulp)
product = expand_binop (mode, umul_widen_optab, op0_low, op1_low,
target, 1, OPTAB_DIRECT);
else
product = expand_binop (mode, smul_widen_optab, op0_low, op1_low,
target, 1, OPTAB_DIRECT);
if (!product)
return NULL_RTX;
product_high = operand_subword (product, high, 1, mode);
adjust = expand_binop (word_mode, add_optab, product_high, adjust,
REG_P (product_high) ? product_high : adjust,
0, OPTAB_DIRECT);
emit_move_insn (product_high, adjust);
return product;
}
/* Wrapper around expand_binop which takes an rtx code to specify
the operation to perform, not an optab pointer. All other
arguments are the same. */
@ -1399,197 +1561,51 @@ expand_binop (enum machine_mode mode, optab binoptab, rtx op0, rtx op1,
delete_insns_since (last);
}
/* If we want to multiply two two-word values and have normal and widening
multiplies of single-word values, we can do this with three smaller
multiplications. Note that we do not make a REG_NO_CONFLICT block here
because we are not operating on one word at a time.
The multiplication proceeds as follows:
_______________________
[__op0_high_|__op0_low__]
_______________________
* [__op1_high_|__op1_low__]
_______________________________________________
_______________________
(1) [__op0_low__*__op1_low__]
_______________________
(2a) [__op0_low__*__op1_high_]
_______________________
(2b) [__op0_high_*__op1_low__]
_______________________
(3) [__op0_high_*__op1_high_]
This gives a 4-word result. Since we are only interested in the
lower 2 words, partial result (3) and the upper words of (2a) and
(2b) don't need to be calculated. Hence (2a) and (2b) can be
calculated using non-widening multiplication.
(1), however, needs to be calculated with an unsigned widening
multiplication. If this operation is not directly supported we
try using a signed widening multiplication and adjust the result.
This adjustment works as follows:
If both operands are positive then no adjustment is needed.
If the operands have different signs, for example op0_low < 0 and
op1_low >= 0, the instruction treats the most significant bit of
op0_low as a sign bit instead of a bit with significance
2**(BITS_PER_WORD-1), i.e. the instruction multiplies op1_low
with 2**BITS_PER_WORD - op0_low, and two's complements the
result. Conclusion: We need to add op1_low * 2**BITS_PER_WORD to
the result.
Similarly, if both operands are negative, we need to add
(op0_low + op1_low) * 2**BITS_PER_WORD.
We use a trick to adjust quickly. We logically shift op0_low right
(op1_low) BITS_PER_WORD-1 steps to get 0 or 1, and add this to
op0_high (op1_high) before it is used to calculate 2b (2a). If no
logical shift exists, we do an arithmetic right shift and subtract
the 0 or -1. */
/* Attempt to synthesize double word multiplies using a sequence of word
mode multiplications. We first attempt to generate a sequence using a
more efficient unsigned widening multiply, and if that fails we then
try using a signed widening multiply. */
if (binoptab == smul_optab
&& class == MODE_INT
&& GET_MODE_SIZE (mode) == 2 * UNITS_PER_WORD
&& smul_optab->handlers[(int) word_mode].insn_code != CODE_FOR_nothing
&& add_optab->handlers[(int) word_mode].insn_code != CODE_FOR_nothing
&& ((umul_widen_optab->handlers[(int) mode].insn_code
!= CODE_FOR_nothing)
|| (smul_widen_optab->handlers[(int) mode].insn_code
!= CODE_FOR_nothing)))
&& add_optab->handlers[(int) word_mode].insn_code != CODE_FOR_nothing)
{
int low = (WORDS_BIG_ENDIAN ? 1 : 0);
int high = (WORDS_BIG_ENDIAN ? 0 : 1);
rtx op0_high = operand_subword_force (op0, high, mode);
rtx op0_low = operand_subword_force (op0, low, mode);
rtx op1_high = operand_subword_force (op1, high, mode);
rtx op1_low = operand_subword_force (op1, low, mode);
rtx product = 0;
rtx op0_xhigh = NULL_RTX;
rtx op1_xhigh = NULL_RTX;
rtx product = NULL_RTX;
/* If the target is the same as one of the inputs, don't use it. This
prevents problems with the REG_EQUAL note. */
if (target == op0 || target == op1
|| (target != 0 && !REG_P (target)))
target = 0;
/* Multiply the two lower words to get a double-word product.
If unsigned widening multiplication is available, use that;
otherwise use the signed form and compensate. */
if (umul_widen_optab->handlers[(int) mode].insn_code != CODE_FOR_nothing)
if (umul_widen_optab->handlers[(int) mode].insn_code
!= CODE_FOR_nothing)
{
product = expand_binop (mode, umul_widen_optab, op0_low, op1_low,
target, 1, OPTAB_DIRECT);
/* If we didn't succeed, delete everything we did so far. */
if (product == 0)
product = expand_doubleword_mult (mode, op0, op1, target,
true, methods);
if (!product)
delete_insns_since (last);
else
op0_xhigh = op0_high, op1_xhigh = op1_high;
}
if (product == 0
if (product == NULL_RTX
&& smul_widen_optab->handlers[(int) mode].insn_code
!= CODE_FOR_nothing)
!= CODE_FOR_nothing)
{
rtx wordm1 = GEN_INT (BITS_PER_WORD - 1);
product = expand_binop (mode, smul_widen_optab, op0_low, op1_low,
target, 1, OPTAB_DIRECT);
op0_xhigh = expand_binop (word_mode, lshr_optab, op0_low, wordm1,
NULL_RTX, 1, next_methods);
if (op0_xhigh)
op0_xhigh = expand_binop (word_mode, add_optab, op0_high,
op0_xhigh, op0_xhigh, 0, next_methods);
else
{
op0_xhigh = expand_binop (word_mode, ashr_optab, op0_low, wordm1,
NULL_RTX, 0, next_methods);
if (op0_xhigh)
op0_xhigh = expand_binop (word_mode, sub_optab, op0_high,
op0_xhigh, op0_xhigh, 0,
next_methods);
}
op1_xhigh = expand_binop (word_mode, lshr_optab, op1_low, wordm1,
NULL_RTX, 1, next_methods);
if (op1_xhigh)
op1_xhigh = expand_binop (word_mode, add_optab, op1_high,
op1_xhigh, op1_xhigh, 0, next_methods);
else
{
op1_xhigh = expand_binop (word_mode, ashr_optab, op1_low, wordm1,
NULL_RTX, 0, next_methods);
if (op1_xhigh)
op1_xhigh = expand_binop (word_mode, sub_optab, op1_high,
op1_xhigh, op1_xhigh, 0,
next_methods);
}
product = expand_doubleword_mult (mode, op0, op1, target,
false, methods);
if (!product)
delete_insns_since (last);
}
/* If we have been able to directly compute the product of the
low-order words of the operands and perform any required adjustments
of the operands, we proceed by trying two more multiplications
and then computing the appropriate sum.
We have checked above that the required addition is provided.
Full-word addition will normally always succeed, especially if
it is provided at all, so we don't worry about its failure. The
multiplication may well fail, however, so we do handle that. */
if (product && op0_xhigh && op1_xhigh)
if (product != NULL_RTX)
{
rtx product_high = operand_subword (product, high, 1, mode);
rtx temp = expand_binop (word_mode, binoptab, op0_low, op1_xhigh,
NULL_RTX, 0, OPTAB_DIRECT);
if (!REG_P (product_high))
product_high = force_reg (word_mode, product_high);
if (temp != 0)
temp = expand_binop (word_mode, add_optab, temp, product_high,
product_high, 0, next_methods);
if (temp != 0 && temp != product_high)
emit_move_insn (product_high, temp);
if (temp != 0)
temp = expand_binop (word_mode, binoptab, op1_low, op0_xhigh,
NULL_RTX, 0, OPTAB_DIRECT);
if (temp != 0)
temp = expand_binop (word_mode, add_optab, temp,
product_high, product_high,
0, next_methods);
if (temp != 0 && temp != product_high)
emit_move_insn (product_high, temp);
emit_move_insn (operand_subword (product, high, 1, mode), product_high);
if (temp != 0)
if (mov_optab->handlers[(int) mode].insn_code != CODE_FOR_nothing)
{
if (mov_optab->handlers[(int) mode].insn_code != CODE_FOR_nothing)
{
temp = emit_move_insn (product, product);
set_unique_reg_note (temp,
REG_EQUAL,
gen_rtx_fmt_ee (MULT, mode,
copy_rtx (op0),
copy_rtx (op1)));
}
return product;
temp = emit_move_insn (target ? target : product, product);
set_unique_reg_note (temp,
REG_EQUAL,
gen_rtx_fmt_ee (MULT, mode,
copy_rtx (op0),
copy_rtx (op1)));
}
return product;
}
/* If we get here, we couldn't do it for some reason even though we
originally thought we could. Delete anything we've emitted in
trying to do it. */
delete_insns_since (last);
}
/* It can't be open-coded in this mode.