On Wed, May 18, 2022 at 7:30 PM Roger Sayle <ro...@nextmovesoftware.com> wrote:
>
>
> Hi Uros,
> Very many thanks for the speedy review and approval of my ix86_rtx_costs
> patch to correct the cost of multi-word multiplications. In the same
> spirit, this patch tidies up a few additional nits I noticed while there:
> Multi-word NOT requires two operations, but multi-word NEG requires
> three operations. Using SSE, vector NOT requires a pxor with -1, but
> AND of NOT is cheap thanks to the existence of pandn. There's also some
> legacy (aka incorrect) logic explicitly testing for DImode [independently
> of TARGET_64BIT] in determining the cost of logic operations that's not
> required.
>
> There should be no behavioural changes from this patch (as confirmed by
> testing) but hopefully vectorization and other middle-end passes can now
> rely on more sensible "cost" estimates.
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}, with
> no new failures. Ok for mainline?
>
>
> 2022-05-18 Roger Sayle <ro...@nextmovesoftware.com>
>
> gcc/ChangeLog
> * config/i386/i386.cc (ix86_rtx_costs): Split AND from XOR/IOR.
> Multi-word binary logic operations require two instructions.
> For vector integer modes, AND with a NOT operand requires only
> a single instruction (pandn).
> [NOT]: Vector integer NOT requires more than 1 instruction (pxor).
> [NEG]: Multi-word negation requires 3 instructions.
- case AND:
case IOR:
case XOR:
if (GET_MODE_CLASS (mode) == MODE_INT
&& GET_MODE_SIZE (mode) > UNITS_PER_WORD)
{
- *total = (cost->add * 2
- + (rtx_cost (XEXP (x, 0), mode, outer_code, opno, speed)
- << (GET_MODE (XEXP (x, 0)) != DImode))
- + (rtx_cost (XEXP (x, 1), mode, outer_code, opno, speed)
- << (GET_MODE (XEXP (x, 1)) != DImode)));
+ *total = cost->add * 2
+ + rtx_cost (XEXP (x, 0), mode, outer_code, opno, speed)
+ + rtx_cost (XEXP (x, 1), mode, outer_code, opno, speed);
+ return true;
+ }
+ else if (GET_MODE_CLASS (mode) == MODE_VECTOR_INT)
+ *total = ix86_vec_cost (mode, cost->sse_op);
+ else if (GET_MODE_SIZE (mode) > UNITS_PER_WORD)
+ *total = cost->add * 2;
+ else
+ *total = cost->add;
+ return false;
Shouldn't this be just:
if (GET_MODE_CLASS (mode) == MODE_VECTOR_INT)
*total = ix86_vec_cost (mode, cost->sse_op);
else if (GET_MODE_SIZE (mode) > UNITS_PER_WORD)
*total = cost->add * 2;
else
*total = cost->add;
return false;
When returning false, subexpressions will be scanned automatically.
+ else if (GET_MODE_CLASS (mode) == MODE_VECTOR_INT)
+ {
+ /* pandn is a single instruction. */
+ if (GET_CODE (XEXP (x, 0)) == NOT)
pandn is also a single instruction with BMI. IMO, this should be also
reflected in RTX costs.
Uros.
