[PATCH] Introduce sh_mul and uh_mul RTX codes for high-part multiplications
This patch introduces new RTX codes to allow the RTL passes and
backends to consistently represent high-part multiplications.
Currently, the RTL used by different backends for expanding
smul3_highpart and umul3_highpart varies greatly,
with many but not all choosing to express this something like:
(define_insn "smuldi3_highpart"
[(set (match_operand:DI 0 "nvptx_register_operand" "=R")
(truncate:DI
(lshiftrt:TI
(mult:TI (sign_extend:TI
(match_operand:DI 1 "nvptx_register_operand" "R"))
(sign_extend:TI
(match_operand:DI 2 "nvptx_register_operand" "R")))
(const_int 64]
""
"%.\\tmul.hi.s64\\t%0, %1, %2;")
One complication with using this "widening multiplication" representation
is that it requires an intermediate in a wider mode, making it difficult
or impossible to encode a high-part multiplication of the widest supported
integer mode. A second is that it can interfere with optimization; for
example simplify-rtx.c contains the comment:
case TRUNCATE:
/* Don't optimize (lshiftrt (mult ...)) as it would interfere
with the umulXi3_highpart patterns. */
Hopefully these problems are solved (or reduced) by introducing a
new canonical form for high-part multiplications in RTL passes.
This also simplifies insn patterns when one operand is constant.
Whilst implementing some constant folding simplifications and
compile-time evaluation of these new RTX codes, I noticed that
this functionality could also be added for the existing saturating
arithmetic RTX codes. Then likewise when documenting these new RTX
codes, I also took the opportunity to silence the @xref warnings in
invoke.texi.
This patch has been tested on x86_64-pc-linux-gnu with "make bootstrap"
and "make -k check" with no new failures. Ok for mainline?
2021-09-25 Roger Sayle
gcc/ChangeLog
* gcc/rtl.def (SH_MULT, UH_MULT): New RTX codes for representing
signed and unsigned high-part multiplication respectively.
* gcc/simplify-rtx.c (simplify_binary_operation_1) [SH_MULT,
UH_MULT]: Simplify high-part multiplications by zero.
[SS_PLUS, US_PLUS, SS_MINUS, US_MINUS, SS_MULT, US_MULT,
SS_DIV, US_DIV]: Similar simplifications for saturating
arithmetic.
(simplify_const_binary_operation) [SS_PLUS, US_PLUS, SS_MINUS,
US_MINUS, SS_MULT, US_MULT, SH_MULT, UH_MULT]: Implement
compile-time evaluation for constant operands.
* gcc/dwarf2out.c (mem_loc_descriptor): Skip SH_MULT and UH_MULT.
* doc/rtl.texi (sh_mult, uhmult): Document new RTX codes.
* doc/md.texi (smul@var{m}3_highpart, umul@var{m3}_highpart):
Mention the new sh_mul and uh_mul RTX codes.
* doc/invoke.texi: Silence @xref "compilation" warnings.
Roger
--
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 4acb941..2de7d99 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -3125,7 +3125,7 @@ errors if these functions are not inlined everywhere they
are called.
@itemx -fno-modules-ts
@opindex fmodules-ts
@opindex fno-modules-ts
-Enable support for C++20 modules (@xref{C++ Modules}). The
+Enable support for C++20 modules, see @xref{C++ Modules}. The
@option{-fno-modules-ts} is usually not needed, as that is the
default. Even though this is a C++20 feature, it is not currently
implicitly enabled by selecting that standard version.
@@ -33553,7 +33553,7 @@ version selected, although in pre-C++20 versions, it is
of course an
extension.
No new source file suffixes are required or supported. If you wish to
-use a non-standard suffix (@xref{Overall Options}), you also need
+use a non-standard suffix, see @xref{Overall Options}, you also need
to provide a @option{-x c++} option too.@footnote{Some users like to
distinguish module interface files with a new suffix, such as naming
the source @code{module.cppm}, which involves
@@ -33615,8 +33615,8 @@ to be resolved at the end of compilation. Without
this, imported
macros are only resolved when expanded or (re)defined. This option
detects conflicting import definitions for all macros.
-@xref{C++ Module Mapper} for details of the @option{-fmodule-mapper}
-family of options.
+For details of the @option{-fmodule-mapper} family of options,
+see @xref{C++ Module Mapper}.
@menu
* C++ Module Mapper:: Module Mapper
@@ -33833,8 +33833,8 @@ dialect used and imports of the module.@footnote{The
precise contents
of this output may change.} The timestamp is the same value as that
provided by the @code{__DATE__} & @code{__TIME__} macros, and may be
explicitly specified with the environment variable
-@code{SOURCE_DATE_EPOCH}. @xref{Environment Variables} for further
-details.
+@code{SOURCE_DATE_EPOCH}. For further details see
+@xref{Environment Variables}.
A set of related CMIs may be copied, provided the relative pathnames
are preserved.
diff --git a/gcc/doc/md.texi b/gcc/doc/m
Re: [PATCH] Introduce sh_mul and uh_mul RTX codes for high-part multiplications
On Sep 25 2021, Roger Sayle wrote:
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 4acb941..2de7d99 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -3125,7 +3125,7 @@ errors if these functions are not inlined everywhere
> they are called.
> @itemx -fno-modules-ts
> @opindex fmodules-ts
> @opindex fno-modules-ts
> -Enable support for C++20 modules (@xref{C++ Modules}). The
> +Enable support for C++20 modules, see @xref{C++ Modules}. The
Or (@pxref{...}).
Andreas.
--
Andreas Schwab, sch...@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
"And now for something completely different."
Re: [PATCH] Introduce sh_mul and uh_mul RTX codes for high-part multiplications
"Roger Sayle" writes:
> This patch introduces new RTX codes to allow the RTL passes and
> backends to consistently represent high-part multiplications.
> Currently, the RTL used by different backends for expanding
> smul3_highpart and umul3_highpart varies greatly,
> with many but not all choosing to express this something like:
>
> (define_insn "smuldi3_highpart"
> [(set (match_operand:DI 0 "nvptx_register_operand" "=R")
>(truncate:DI
> (lshiftrt:TI
> (mult:TI (sign_extend:TI
>(match_operand:DI 1 "nvptx_register_operand" "R"))
> (sign_extend:TI
>(match_operand:DI 2 "nvptx_register_operand" "R")))
> (const_int 64]
> ""
> "%.\\tmul.hi.s64\\t%0, %1, %2;")
>
> One complication with using this "widening multiplication" representation
> is that it requires an intermediate in a wider mode, making it difficult
> or impossible to encode a high-part multiplication of the widest supported
> integer mode.
Yeah. It's also a problem when representing vector ops.
> A second is that it can interfere with optimization; for
> example simplify-rtx.c contains the comment:
>
>case TRUNCATE:
> /* Don't optimize (lshiftrt (mult ...)) as it would interfere
> with the umulXi3_highpart patterns. */
>
> Hopefully these problems are solved (or reduced) by introducing a
> new canonical form for high-part multiplications in RTL passes.
> This also simplifies insn patterns when one operand is constant.
>
> Whilst implementing some constant folding simplifications and
> compile-time evaluation of these new RTX codes, I noticed that
> this functionality could also be added for the existing saturating
> arithmetic RTX codes. Then likewise when documenting these new RTX
> codes, I also took the opportunity to silence the @xref warnings in
> invoke.texi.
>
> This patch has been tested on x86_64-pc-linux-gnu with "make bootstrap"
> and "make -k check" with no new failures. Ok for mainline?
>
>
> 2021-09-25 Roger Sayle
>
> gcc/ChangeLog
> * gcc/rtl.def (SH_MULT, UH_MULT): New RTX codes for representing
> signed and unsigned high-part multiplication respectively.
> * gcc/simplify-rtx.c (simplify_binary_operation_1) [SH_MULT,
> UH_MULT]: Simplify high-part multiplications by zero.
> [SS_PLUS, US_PLUS, SS_MINUS, US_MINUS, SS_MULT, US_MULT,
> SS_DIV, US_DIV]: Similar simplifications for saturating
> arithmetic.
> (simplify_const_binary_operation) [SS_PLUS, US_PLUS, SS_MINUS,
> US_MINUS, SS_MULT, US_MULT, SH_MULT, UH_MULT]: Implement
> compile-time evaluation for constant operands.
> * gcc/dwarf2out.c (mem_loc_descriptor): Skip SH_MULT and UH_MULT.
> * doc/rtl.texi (sh_mult, uhmult): Document new RTX codes.
> * doc/md.texi (smul@var{m}3_highpart, umul@var{m3}_highpart):
> Mention the new sh_mul and uh_mul RTX codes.
> * doc/invoke.texi: Silence @xref "compilation" warnings.
Look like a good idea to me. Only real comment is on the naming:
if possible, I think we should try to avoid introducing yet more
differences between optab names and rtl codes. How about umul_highpart
for the unsigned code, to match both the optab and the existing
convention of adding “u” directly to the front of non-saturating
operations?
Things are more inconsistent for signed rtx codes: sometimes the
“s” is present and sometimes it isn't. But since “smin” and “smax”
have it, I think we can justify having it here too.
So I think we should use smul_highpart and umul_highpart.
It's a bit more wordy than sh_mul, but still a lot shorter than
the status quo ;-)
> diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
> index ebad5cb..b4b04b9 100644
> --- a/gcc/simplify-rtx.c
> +++ b/gcc/simplify-rtx.c
> @@ -4142,11 +4142,40 @@ simplify_context::simplify_binary_operation_1
> (rtx_code code,
> case US_PLUS:
> case SS_MINUS:
> case US_MINUS:
> + /* Simplify x + 0 to x, if possible. */
Nit: +/-
> + if (trueop1 == CONST0_RTX (mode) && !HONOR_SIGNED_ZEROS (mode))
The HONOR_SIGNED_ZEROS check is redundant, since these ops don't support
modes with signed zero.
Same for the other HONOR_* macros in the patch. E.g. I don't think
we should try to guess how infinities and saturation work together.
> + return op0;
> + return 0;
> +
> case SS_MULT:
> case US_MULT:
> + /* Simplify x * 0 to 0, if possible. */
> + if (trueop1 == CONST0_RTX (mode)
> + && !HONOR_NANS (mode)
> + && !HONOR_SIGNED_ZEROS (mode)
> + && !side_effects_p (op0))
> + return op1;
> +
> + /* Simplify x * 1 to x, if possible. */
> + if (trueop1 == CONST1_RTX (mode) && !HONOR_SNANS (mode))
> + return op0;
> + return 0;
> +
> +case SH_MULT:
> +case UH_MULT:
> + /* Simplify x * 0 to 0, if possible. */
> + if (trueop1 == CONST0_RTX (mode)
> + && !HONOR_NANS (mode)
> + && !HONOR_
