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Add comment to expand_mult max_cost change. 

From-SVN: r104379
This commit is contained in:
David Edelsohn 2005-09-17 19:08:03 -04:00
parent 579ad6bf42
commit 5e839bc820
1 changed files with 8 additions and 4 deletions
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12
gcc/expmed.c
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@ -3022,7 +3022,7 @@ expand_mult (enum machine_mode mode, rtx op0, rtx op1, rtx target,
&& (unsignedp || !flag_trapv))
{
HOST_WIDE_INT coeff = 0;
rtx reg = gen_raw_REG (mode, LAST_VIRTUAL_REGISTER + 1);
rtx fake_reg = gen_raw_REG (mode, LAST_VIRTUAL_REGISTER + 1);
/* synth_mult does an `unsigned int' multiply. As long as the mode is
less than or equal in size to `unsigned int' this doesn't matter.
@ -3040,8 +3040,10 @@ expand_mult (enum machine_mode mode, rtx op0, rtx op1, rtx target,
&& GET_MODE_BITSIZE (mode) > HOST_BITS_PER_WIDE_INT)
{
/* Its safe to use -INTVAL (op1) even for INT_MIN, as the
result is interpreted as an unsigned coefficient. */
max_cost = rtx_cost (gen_rtx_MULT (mode, reg, op1), SET)
result is interpreted as an unsigned coefficient.
Exclude cost of op0 from max_cost to match the cost
calculation of the synth_mult. */
max_cost = rtx_cost (gen_rtx_MULT (mode, fake_reg, op1), SET)
- neg_cost[mode];
if (max_cost > 0
&& choose_mult_variant (mode, -INTVAL (op1), &algorithm,
@ -3084,7 +3086,9 @@ expand_mult (enum machine_mode mode, rtx op0, rtx op1, rtx target,
build_int_cst (NULL_TREE, floor_log2 (coeff)),
target, unsignedp);
max_cost = rtx_cost (gen_rtx_MULT (mode, reg, op1), SET);
/* Exclude cost of op0 from max_cost to match the cost
calculation of the synth_mult. */
max_cost = rtx_cost (gen_rtx_MULT (mode, fake_reg, op1), SET);
if (choose_mult_variant (mode, coeff, &algorithm, &variant,
max_cost))
return expand_mult_const (mode, op0, coeff, target,