Trunk expand_mult uses the following code to handle CONST_DOUBLEs:
/* If we are multiplying in DImode, it may still be a win
to try to work with shifts and adds. */
if (CONST_DOUBLE_HIGH (scalar_op1) == 0
&& (CONST_DOUBLE_LOW (scalar_op1) > 0
|| (CONST_DOUBLE_LOW (scalar_op1) < 0
&& EXACT_POWER_OF_2_OR_ZERO_P
(CONST_DOUBLE_LOW (scalar_op1)))))
{
coeff = CONST_DOUBLE_LOW (scalar_op1);
is_neg = false;
}
else if (CONST_DOUBLE_LOW (scalar_op1) == 0)
{
coeff = CONST_DOUBLE_HIGH (scalar_op1);
if (EXACT_POWER_OF_2_OR_ZERO_P (coeff))
{
int shift = floor_log2 (coeff) + HOST_BITS_PER_WIDE_INT;
if (shift < HOST_BITS_PER_DOUBLE_INT - 1
|| mode_bitsize <= HOST_BITS_PER_DOUBLE_INT)
return expand_shift (LSHIFT_EXPR, mode, op0,
shift, target, unsignedp);
}
goto skip_synth;
}
else
goto skip_synth;
So the only non-power-of-2 case that avoids the skip_synth treatment
is a CONST_DOUBLE whose high HWI is 0 and whose low HWI is positive.
I think that's outdated, because even on trunk such constants should be
CONST_INTs instead. They definitely are on wide-int. So we only need
to handle the power-of-2 case.
The shift handling for that case can be much simpler. We're dealing
with a constant in a particular mode, so if exact_log2 returns >= 0,
it's a valid shift for that mode. No truncation or boundary checks
are needed. wide ints really clean this up.
The same reasoning applies to simplify_binary_operation_1, except there
we're just saving a redundant upper bound test.
Tested on powerpc64-linux-gnu and by rerunning the assembly comparison.
OK to install?
Thanks,
Richard
Index: gcc/expmed.c
===================================================================
--- gcc/expmed.c 2013-11-09 10:50:12.836314443 +0000
+++ gcc/expmed.c 2013-11-09 10:50:37.333494113 +0000
@@ -3075,30 +3075,11 @@ expand_mult (enum machine_mode mode, rtx
else if (CONST_DOUBLE_AS_INT_P (scalar_op1))
#endif
{
- int p = GET_MODE_PRECISION (mode);
int shift = wi::exact_log2 (std::make_pair (scalar_op1, mode));
- /* Perfect power of 2. */
- is_neg = false;
+ /* Perfect power of 2 (other than 1, which is handled above). */
if (shift > 0)
- {
- /* Do the shift count trucation against the bitsize, not
- the precision. See the comment above
- wide-int.c:trunc_shift for details. */
- if (SHIFT_COUNT_TRUNCATED)
- shift &= GET_MODE_BITSIZE (mode) - 1;
- /* We could consider adding just a move of 0 to target
- if the shift >= p */
- if (shift < p)
- return expand_shift (LSHIFT_EXPR, mode, op0,
- shift, target, unsignedp);
- /* Any positive number that fits in a word. */
- coeff = CONST_WIDE_INT_ELT (scalar_op1, 0);
- }
- else if (wi::sign_mask (std::make_pair (scalar_op1, mode)) == 0)
- {
- /* Any positive number that fits in a word. */
- coeff = CONST_WIDE_INT_ELT (scalar_op1, 0);
- }
+ return expand_shift (LSHIFT_EXPR, mode, op0,
+ shift, target, unsignedp);
else
goto skip_synth;
}
Index: gcc/simplify-rtx.c
===================================================================
--- gcc/simplify-rtx.c 2013-11-09 10:50:12.836314443 +0000
+++ gcc/simplify-rtx.c 2013-11-09 10:50:14.046323332 +0000
@@ -2399,7 +2399,7 @@ simplify_binary_operation_1 (enum rtx_co
if (CONST_SCALAR_INT_P (trueop1))
{
val = wi::exact_log2 (std::make_pair (trueop1, mode));
- if (val >= 0 && val < GET_MODE_BITSIZE (mode))
+ if (val >= 0)
return simplify_gen_binary (ASHIFT, mode, op0, GEN_INT (val));
}
