On 1/2/23 10:30, ro...@nextmovesoftware.com wrote:
Hi Jeff,
On 2 Jan 2023, at 15:45, Jeff Law <jeffreya...@gmail.com> wrote:
On 1/1/23 08:55, Roger Sayle wrote:
In 2011, the rtl.texi documentation was updated to reflect that the
modes of the RTX unary operations FFS, POPCOUNT and PARITY must
match those of their operands. Unfortunately, some of the transformations
in simplify-rtx.cc predate this tightening of RTL semantics, and have
not (until now) been updated/fixed. i.e. The POPCOUNT and PARITY
optimizations were "correct" when I originally added them back in 2007.
Segher requested that I split this piece out from a fix for PR 106594 in
https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601501.html
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?
2023-01-01 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
* gcc/simplify-rtx.cc (simplify_unary_operation_1) <case FFS>:
Avoid generating FFS with mismatched operand and result modes, by
using an explicit SIGN_EXTEND/ZERO_EXTEND instead.
<case POPCOUNT>: Likewise, for POPCOUNT of ZERO_EXTEND.
<case PARITY>: Likewise, for PARITY of {ZERO,SIGN}_EXTEND.
?!? The docs still seem to indicate to me that the modes of the input and
output operands can differ.
Let's take PARITY as an example:
@cindex @code{parity@var{m}2} instruction pattern
@item @samp{parity@var{m}2}
Store into operand 0 the parity of operand 1, i.e.@: the number of 1-bits
in operand 1 modulo 2.
@var{m} is either a scalar or vector integer mode. When it is a scalar,
operand 1 has mode @var{m} but operand 0 can have whatever scalar
integer mode is suitable for the target.
The mode of the pattern name has to match the mode of the input operand. The
mode of the
output operand can differ from the mode of the input operand. we seem to have
a disagreement
on the documented semantics of these opcodes.
The documentation that you're looking at is the definition of the parity optab
in
md.texi, not the definition of the PARITY rtx in rtl.texi. The distinction is
subtle.
Hence a backend can define paritysiqi2 but in the RTL pattern it expands to the
unary PARITY operator must have the same result type as its operand type,
wrapped in either a truncate or extension if necessary.
Hmm, yea I was looking at md.texi, not rtl.texi. I'll take a look at
the latter after I get some coffee.
Thanks!
jeff
