On 11/09/2013 05:51 AM, Richard Sandiford wrote:
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 I think that's outdated, because even on trunk such constants should be CONST_INTs instead.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)); }
looks good to me. kenny
