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expmed.c (expand_shift): Consider expanding LSHIFT_EXPR by a constant as a sequence of additions... 

* expmed.c (expand_shift): Consider expanding LSHIFT_EXPR by a
	constant as a sequence of additions depending upon the rtx_costs.
	(synth_mult): Update the "observed" cost of a shift, based upon
	the above optimization.

From-SVN: r83956
This commit is contained in:
Roger Sayle 2004-07-01 04:27:09 +00:00 committed by Roger Sayle
parent f8a57be818
commit 15bad393a1
2 changed files with 31 additions and 1 deletions
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7
gcc/ChangeLog
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@ -1,3 +1,10 @@
2004-06-30 Roger Sayle <roger@eyesopen.com>
* expmed.c (expand_shift): Consider expanding LSHIFT_EXPR by a
constant as a sequence of additions depending upon the rtx_costs.
(synth_mult): Update the "observed" cost of a shift, based upon
the above optimization.
2004-06-28 Geoffrey Keating <geoffk@apple.com>
Andreas Tobler <a.tobler@schweiz.ch>

25
gcc/expmed.c
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@ -2017,6 +2017,24 @@ expand_shift (enum tree_code code, enum machine_mode mode, rtx shifted,
if (op1 == const0_rtx)
return shifted;
/* Check whether its cheaper to implement a left shift by a constant
bit count by a sequence of additions. */
if (code == LSHIFT_EXPR
&& GET_CODE (op1) == CONST_INT
&& INTVAL (op1) > 0
&& INTVAL (op1) < GET_MODE_BITSIZE (mode)
&& shift_cost[mode][INTVAL (op1)] > INTVAL (op1) * add_cost[mode])
{
int i;
for (i = 0; i < INTVAL (op1); i++)
{
temp = force_reg (mode, shifted);
shifted = expand_binop (mode, add_optab, temp, temp, NULL_RTX,
unsignedp, OPTAB_LIB_WIDEN);
}
return shifted;
}
for (try = 0; temp == 0 && try < 3; try++)
{
enum optab_methods methods;
@ -2242,7 +2260,12 @@ synth_mult (struct algorithm *alg_out, unsigned HOST_WIDE_INT t,
if (m < maxm)
{
q = t >> m;
cost = shift_cost[mode][m];
/* The function expand_shift will choose between a shift and
a sequence of additions, so the observed cost is given as
MIN (m * add_cost[mode], shift_cost[mode][m]). */
cost = m * add_cost[mode];
if (shift_cost[mode][m] < cost)
cost = shift_cost[mode][m];
synth_mult (alg_in, q, cost_limit - cost, mode);
cost += alg_in->cost;