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expmed.c (expand_sdiv_pow2): New function to expand signed division by a positive power of two...

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* expmed.c (expand_sdiv_pow2): New function to expand signed division
	by a positive power of two, split out from expand_divmod.  Provide
	an alternate implementation when shifts are expensive.  Lower the
	threshold for using a branchless implementation to BRANCH_COST >= 2.
	(expand_divmod): Call expand_sdiv_pow2 for suitable divisions.

From-SVN: r84686
This commit is contained in:
Roger Sayle 2004-07-14 13:50:39 +00:00 committed by Roger Sayle
parent 51a61243e7
commit 39cab01994
2 changed files with 57 additions and 32 deletions
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8
gcc/ChangeLog
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@ -1,3 +1,11 @@
2004-07-14 Roger Sayle <roger@eyesopen.com>
* expmed.c (expand_sdiv_pow2): New function to expand signed division
by a positive power of two, split out from expand_divmod. Provide
an alternate implementation when shifts are expensive. Lower the
threshold for using a branchless implementation to BRANCH_COST >= 2.
(expand_divmod): Call expand_sdiv_pow2 for suitable divisions.
2004-07-14 Paolo Bonzini <bonzini@gnu.org>
* tree-dfa.c (make_rename_temp): *Really* work just

81
gcc/expmed.c
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@ -52,6 +52,7 @@ static rtx extract_split_bit_field (rtx, unsigned HOST_WIDE_INT,
unsigned HOST_WIDE_INT, int);
static void do_cmp_and_jump (rtx, rtx, enum rtx_code, enum machine_mode, rtx);
static rtx expand_smod_pow2 (enum machine_mode, rtx, HOST_WIDE_INT);
static rtx expand_sdiv_pow2 (enum machine_mode, rtx, HOST_WIDE_INT);
/* Nonzero means divides or modulus operations are relatively cheap for
powers of two, so don't use branches; emit the operation instead.
@ -3170,6 +3171,53 @@ expand_smod_pow2 (enum machine_mode mode, rtx op0, HOST_WIDE_INT d)
emit_label (label);
return result;
}
/* Expand signed division of OP0 by a power of two D in mode MODE.
This routine is only called for positive values of D. */
static rtx
expand_sdiv_pow2 (enum machine_mode mode, rtx op0, HOST_WIDE_INT d)
{
rtx temp, label;
tree shift;
int logd;
logd = floor_log2 (d);
shift = build_int_2 (logd, 0);
if (d == 2 && BRANCH_COST >= 1)
{
temp = gen_reg_rtx (mode);
temp = emit_store_flag (temp, LT, op0, const0_rtx, mode, 0, 1);
temp = expand_binop (mode, add_optab, temp, op0, NULL_RTX,
0, OPTAB_LIB_WIDEN);
return expand_shift (RSHIFT_EXPR, mode, temp, shift, NULL_RTX, 0);
}
if (BRANCH_COST >= 2)
{
int ushift = GET_MODE_BITSIZE (mode) - logd;
temp = gen_reg_rtx (mode);
temp = emit_store_flag (temp, LT, op0, const0_rtx, mode, 0, -1);
if (shift_cost[mode][ushift] > COSTS_N_INSNS (1))
temp = expand_binop (mode, and_optab, temp, GEN_INT (d - 1),
NULL_RTX, 0, OPTAB_LIB_WIDEN);
else
temp = expand_shift (RSHIFT_EXPR, mode, temp,
build_int_2 (ushift, 0), NULL_RTX, 1);
temp = expand_binop (mode, add_optab, temp, op0, NULL_RTX,
0, OPTAB_LIB_WIDEN);
return expand_shift (RSHIFT_EXPR, mode, temp, shift, NULL_RTX, 0);
}
label = gen_label_rtx ();
temp = copy_to_mode_reg (mode, op0);
do_cmp_and_jump (temp, const0_rtx, GE, mode, label);
expand_inc (temp, GEN_INT (d - 1));
emit_label (label);
return expand_shift (RSHIFT_EXPR, mode, temp, shift, NULL_RTX, 0);
}
/* Emit the code to divide OP0 by OP1, putting the result in TARGET
if that is convenient, and returning where the result is.
@ -3582,38 +3630,7 @@ expand_divmod (int rem_flag, enum tree_code code, enum machine_mode mode,
if (remainder)
return gen_lowpart (mode, remainder);
}
lgup = floor_log2 (abs_d);
if (BRANCH_COST < 1 || (abs_d != 2 && BRANCH_COST < 3))
{
rtx label = gen_label_rtx ();
rtx t1;
t1 = copy_to_mode_reg (compute_mode, op0);
do_cmp_and_jump (t1, const0_rtx, GE,
compute_mode, label);
expand_inc (t1, gen_int_mode (abs_d - 1,
compute_mode));
emit_label (label);
quotient = expand_shift (RSHIFT_EXPR, compute_mode, t1,
build_int_2 (lgup, 0),
tquotient, 0);
}
else
{
rtx t1, t2, t3;
t1 = expand_shift (RSHIFT_EXPR, compute_mode, op0,
build_int_2 (size - 1, 0),
NULL_RTX, 0);
t2 = expand_shift (RSHIFT_EXPR, compute_mode, t1,
build_int_2 (size - lgup, 0),
NULL_RTX, 1);
t3 = force_operand (gen_rtx_PLUS (compute_mode,
op0, t2),
NULL_RTX);
quotient = expand_shift (RSHIFT_EXPR, compute_mode, t3,
build_int_2 (lgup, 0),
tquotient, 0);
}
quotient = expand_sdiv_pow2 (compute_mode, op0, abs_d);
/* We have computed OP0 / abs(OP1). If OP1 is negative,
negate the quotient. */