"Roger Sayle" <ro...@nextmovesoftware.com> writes:
> Hi Richard,
>
> All excellent suggestions. The revised patch below implements all of
> your (and Andreas') recommendations. I'm happy to restrict GCC's support
> for saturating arithmetic to integer types, even though I do know of one
> target (nvptx) that supports saturating floating point math, where results
> are clamped to [0.0, 1.0], but I've not investigated how NaNs or signed
> zeros are handled.
>
> Good catch on my min/max typo. It convinced me to work harder to come
> up with some test cases for these simplifications, which I've managed to
> trigger on x86_64-pc-linux-gnu in the four new attached test cases.
>
> 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?
>
> 2021-09-29 Roger Sayle <ro...@nextmovesoftware.com>
> Richard Sandiford <richard.sandif...@arm.com>
Thanks for the cite, but I don't think I should be listed here.
I didn't really write anything :-)
The new patch is OK, thanks. I don't know whether the x86 tests need
special markup.
Richard
>
> gcc/ChangeLog
> * gcc/rtl.def (SMUL_HIGHPART, UMUL_HIGHPART): New RTX codes for
> representing signed and unsigned high-part multiplication resp.
> * gcc/simplify-rtx.c (simplify_binary_operation_1) [SMUL_HIGHPART,
> UMUL_HIGHPART]: 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, SMUL_HIGHPART, UMUL_HIGHPART]:
> Implement compile-time evaluation for constant operands.
>
> * gcc/dwarf2out.c (mem_loc_descriptor): Skip SMUL_HIGHPART and
> UMUL_HIGHPART.
> * doc/rtl.texi (smul_highpart, umul_highpart): Document RTX codes.
> * doc/md.texi (smul@var{m}3_highpart, umul@var{m3}_highpart):
> Mention the new smul_highpart and umul_highpart RTX codes.
> * doc/invoke.texi: Silence @xref "compilation" warnings.
>
> gcc/testsuite/ChangeLog
> * gcc.target/i386/sse2-mmx-paddsb-2.c: New test case.
> * gcc.target/i386/sse2-mmx-paddusb-2.c: New test case.
> * gcc.target/i386/sse2-mmx-subsb-2.c: New test case.
> * gcc.target/i386/sse2-mmx-subusb-2.c: New test case.
>
> Roger
> --
>
> -----Original Message-----
> From: Richard Sandiford <richard.sandif...@arm.com>
> Sent: 27 September 2021 16:44
> To: Roger Sayle <ro...@nextmovesoftware.com>
> Cc: 'GCC Patches' <gcc-patches@gcc.gnu.org>
> Subject: Re: [PATCH] Introduce sh_mul and uh_mul RTX codes for high-part
> multiplications
>
> "Roger Sayle" <ro...@nextmovesoftware.com> 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
>> smul<mode>3_highpart and umul<mode>3_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 <ro...@nextmovesoftware.com>
>>
>> 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_SIGNED_ZEROS (mode)
>> + && !side_effects_p (op0))
>> + return op1;
>> + return 0;
>> +
>> case SS_DIV:
>> case US_DIV:
>> - /* ??? There are simplifications that can be done. */
>> + /* Simplify x / 1 to x, if possible. */
>> + if (trueop1 == CONST1_RTX (mode) && !HONOR_SNANS (mode))
>> + return op0;
>> return 0;
>>
>> case VEC_SERIES:
>> @@ -5011,6 +5040,63 @@ simplify_const_binary_operation (enum rtx_code code,
>> machine_mode mode,
>> }
>> break;
>> }
>> +
>> + case SS_PLUS:
>> + result = wi::add (pop0, pop1, SIGNED, &overflow);
>
> I think a goto label would be good here, so that later signed ops can reuse
> this code instead of having to repeat it.
> Same idea for the unsigned case.
>
>> + if (overflow == wi::OVF_OVERFLOW)
>> + result = wi::max_value (GET_MODE_PRECISION (int_mode), SIGNED);
>> + else if (overflow == wi::OVF_UNDERFLOW)
>> + result = wi::max_value (GET_MODE_PRECISION (int_mode), SIGNED);
>
> Should be min_value. Same for the other underflow handlers.
>
> Like Andreas said, @pxref would be better where applicable.
>
> Thanks,
> Richard
>
>> + else if (overflow != wi::OVF_NONE)
>> + return NULL_RTX;
>> + break;
>> +
>> + case US_PLUS:
>> + result = wi::add (pop0, pop1, UNSIGNED, &overflow);
>> + if (overflow != wi::OVF_NONE)
>> + result = wi::max_value (GET_MODE_PRECISION (int_mode), UNSIGNED);
>> + break;
>> +
>> + case SS_MINUS:
>> + result = wi::sub (pop0, pop1, SIGNED, &overflow);
>> + if (overflow == wi::OVF_OVERFLOW)
>> + result = wi::max_value (GET_MODE_PRECISION (int_mode), SIGNED);
>> + else if (overflow == wi::OVF_UNDERFLOW)
>> + result = wi::max_value (GET_MODE_PRECISION (int_mode), SIGNED);
>> + else if (overflow != wi::OVF_NONE)
>> + return NULL_RTX;
>> + break;
>> +
>> + case US_MINUS:
>> + result = wi::sub (pop0, pop1, UNSIGNED, &overflow);
>> + if (overflow != wi::OVF_NONE)
>> + result = wi::min_value (GET_MODE_PRECISION (int_mode), UNSIGNED);
>> + break;
>> +
>> + case SS_MULT:
>> + result = wi::mul (pop0, pop1, SIGNED, &overflow);
>> + if (overflow == wi::OVF_OVERFLOW)
>> + result = wi::max_value (GET_MODE_PRECISION (int_mode), SIGNED);
>> + else if (overflow == wi::OVF_UNDERFLOW)
>> + result = wi::max_value (GET_MODE_PRECISION (int_mode), SIGNED);
>> + else if (overflow != wi::OVF_NONE)
>> + return NULL_RTX;
>> + break;
>> +
>> + case US_MULT:
>> + result = wi::mul (pop0, pop1, UNSIGNED, &overflow);
>> + if (overflow != wi::OVF_NONE)
>> + result = wi::max_value (GET_MODE_PRECISION (int_mode), UNSIGNED);
>> + break;
>> +
>> + case SH_MULT:
>> + result = wi::mul_high (pop0, pop1, SIGNED);
>> + break;
>> +
>> + case UH_MULT:
>> + result = wi::mul_high (pop0, pop1, UNSIGNED);
>> + break;
>> +
>> default:
>> return NULL_RTX;
>> }
>
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 4acb941..7ed0c69 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 (@pxref{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 (@pxref{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,
> +@pxref{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
> +@pxref{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/md.texi
> index 2b41cb7..ed35b8f 100644
> --- a/gcc/doc/md.texi
> +++ b/gcc/doc/md.texi
> @@ -5776,11 +5776,13 @@ multiplication.
> @item @samp{smul@var{m}3_highpart}
> Perform a signed multiplication of operands 1 and 2, which have mode
> @var{m}, and store the most significant half of the product in operand 0.
> -The least significant half of the product is discarded.
> +The least significant half of the product is discarded. This may be
> +represented in RTL using a @code{smul_highpart} RTX expression.
>
> @cindex @code{umul@var{m}3_highpart} instruction pattern
> @item @samp{umul@var{m}3_highpart}
> -Similar, but the multiplication is unsigned.
> +Similar, but the multiplication is unsigned. This may be represented
> +in RTL using an @code{umul_highpart} RTX expression.
>
> @cindex @code{madd@var{m}@var{n}4} instruction pattern
> @item @samp{madd@var{m}@var{n}4}
> diff --git a/gcc/doc/rtl.texi b/gcc/doc/rtl.texi
> index e1e76a9..2058997 100644
> --- a/gcc/doc/rtl.texi
> +++ b/gcc/doc/rtl.texi
> @@ -2524,7 +2524,19 @@ not be the same.
> For unsigned widening multiplication, use the same idiom, but with
> @code{zero_extend} instead of @code{sign_extend}.
>
> +@findex smul_highpart
> +@findex umul_highpart
> +@cindex high-part multiplication
> +@cindex multiplication high part
> +@item (smul_highpart:@var{m} @var{x} @var{y})
> +@itemx (umul_highpart:@var{m} @var{x} @var{y})
> +Represents the high-part multiplication of @var{x} and @var{y} carried
> +out in machine mode @var{m}. @code{smul_highpart} returns the high part
> +of a signed multiplication, @code{umul_highpart} returns the high part
> +of an unsigned multiplication.
> +
> @findex fma
> +@cindex fused multiply-add
> @item (fma:@var{m} @var{x} @var{y} @var{z})
> Represents the @code{fma}, @code{fmaf}, and @code{fmal} builtin
> functions, which compute @samp{@var{x} * @var{y} + @var{z}}
> diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
> index 9876750..20f2c5d 100644
> --- a/gcc/dwarf2out.c
> +++ b/gcc/dwarf2out.c
> @@ -16809,6 +16809,8 @@ mem_loc_descriptor (rtx rtl, machine_mode mode,
> case CONST_FIXED:
> case CLRSB:
> case CLOBBER:
> + case SMUL_HIGHPART:
> + case UMUL_HIGHPART:
> break;
>
> case CONST_STRING:
> diff --git a/gcc/rtl.def b/gcc/rtl.def
> index c80144b..5710a2e 100644
> --- a/gcc/rtl.def
> +++ b/gcc/rtl.def
> @@ -467,6 +467,11 @@ DEF_RTL_EXPR(SS_MULT, "ss_mult", "ee", RTX_COMM_ARITH)
> /* Multiplication with unsigned saturation */
> DEF_RTL_EXPR(US_MULT, "us_mult", "ee", RTX_COMM_ARITH)
>
> +/* Signed high-part multiplication. */
> +DEF_RTL_EXPR(SMUL_HIGHPART, "smul_highpart", "ee", RTX_COMM_ARITH)
> +/* Unsigned high-part multiplication. */
> +DEF_RTL_EXPR(UMUL_HIGHPART, "umul_highpart", "ee", RTX_COMM_ARITH)
> +
> /* Operand 0 divided by operand 1. */
> DEF_RTL_EXPR(DIV, "div", "ee", RTX_BIN_ARITH)
> /* Division with signed saturation */
> diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
> index ebad5cb..7e8e2c3 100644
> --- a/gcc/simplify-rtx.c
> +++ b/gcc/simplify-rtx.c
> @@ -4142,11 +4142,36 @@ 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. */
> + if (trueop1 == CONST0_RTX (mode))
> + return op0;
> + return 0;
> +
> case SS_MULT:
> case US_MULT:
> + /* Simplify x * 0 to 0, if possible. */
> + if (trueop1 == CONST0_RTX (mode)
> + && !side_effects_p (op0))
> + return op1;
> +
> + /* Simplify x * 1 to x, if possible. */
> + if (trueop1 == CONST1_RTX (mode))
> + return op0;
> + return 0;
> +
> + case SMUL_HIGHPART:
> + case UMUL_HIGHPART:
> + /* Simplify x * 0 to 0, if possible. */
> + if (trueop1 == CONST0_RTX (mode)
> + && !side_effects_p (op0))
> + return op1;
> + return 0;
> +
> case SS_DIV:
> case US_DIV:
> - /* ??? There are simplifications that can be done. */
> + /* Simplify x / 1 to x, if possible. */
> + if (trueop1 == CONST1_RTX (mode))
> + return op0;
> return 0;
>
> case VEC_SERIES:
> @@ -5011,6 +5036,51 @@ simplify_const_binary_operation (enum rtx_code code,
> machine_mode mode,
> }
> break;
> }
> +
> + case SS_PLUS:
> + result = wi::add (pop0, pop1, SIGNED, &overflow);
> + clamp_signed_saturation:
> + if (overflow == wi::OVF_OVERFLOW)
> + result = wi::max_value (GET_MODE_PRECISION (int_mode), SIGNED);
> + else if (overflow == wi::OVF_UNDERFLOW)
> + result = wi::min_value (GET_MODE_PRECISION (int_mode), SIGNED);
> + else if (overflow != wi::OVF_NONE)
> + return NULL_RTX;
> + break;
> +
> + case US_PLUS:
> + result = wi::add (pop0, pop1, UNSIGNED, &overflow);
> + clamp_unsigned_saturation:
> + if (overflow != wi::OVF_NONE)
> + result = wi::max_value (GET_MODE_PRECISION (int_mode), UNSIGNED);
> + break;
> +
> + case SS_MINUS:
> + result = wi::sub (pop0, pop1, SIGNED, &overflow);
> + goto clamp_signed_saturation;
> +
> + case US_MINUS:
> + result = wi::sub (pop0, pop1, UNSIGNED, &overflow);
> + if (overflow != wi::OVF_NONE)
> + result = wi::min_value (GET_MODE_PRECISION (int_mode), UNSIGNED);
> + break;
> +
> + case SS_MULT:
> + result = wi::mul (pop0, pop1, SIGNED, &overflow);
> + goto clamp_signed_saturation;
> +
> + case US_MULT:
> + result = wi::mul (pop0, pop1, UNSIGNED, &overflow);
> + goto clamp_unsigned_saturation;
> +
> + case SMUL_HIGHPART:
> + result = wi::mul_high (pop0, pop1, SIGNED);
> + break;
> +
> + case UMUL_HIGHPART:
> + result = wi::mul_high (pop0, pop1, UNSIGNED);
> + break;
> +
> default:
> return NULL_RTX;
> }
>
> /* { dg-do compile } */
> /* { dg-options "-O2" } */
>
> typedef char v8qi __attribute__ ((vector_size (8)));
>
> char foo()
> {
> v8qi tx = { 1, 0, 0, 0, 0, 0, 0, 0 };
> v8qi ty = { 2, 0, 0, 0, 0, 0, 0, 0 };
> v8qi t = __builtin_ia32_paddsb(tx, ty);
> return t[0];
> }
>
> char bar()
> {
> v8qi tx = { 100, 0, 0, 0, 0, 0, 0, 0 };
> v8qi ty = { 100, 0, 0, 0, 0, 0, 0, 0 };
> v8qi t = __builtin_ia32_paddsb(tx, ty);
> return t[0];
> }
>
> char baz()
> {
> v8qi tx = { -100, 0, 0, 0, 0, 0, 0, 0 };
> v8qi ty = { -100, 0, 0, 0, 0, 0, 0, 0 };
> v8qi t = __builtin_ia32_paddsb(tx, ty);
> return t[0];
> }
>
> /* { dg-final { scan-assembler-times "movl\[ \\t\]+\\\$3," 1 } } */
> /* { dg-final { scan-assembler-times "movl\[ \\t\]+\\\$127," 1 } } */
> /* { dg-final { scan-assembler-times "movl\[ \\t\]+\\\$-128," 1 } } */
> /* { dg-final { scan-assembler-not "paddsb\[ \\t\]+%xmm\[0-9\]+" } } */
>
>
>
> /* { dg-do compile } */
> /* { dg-options "-O2" } */
>
> typedef char v8qi __attribute__ ((vector_size (8)));
>
> char foo()
> {
> v8qi tx = { 5, 0, 0, 0, 0, 0, 0, 0 };
> v8qi ty = { 2, 0, 0, 0, 0, 0, 0, 0 };
> v8qi t = __builtin_ia32_psubusb(tx, ty);
> return t[0];
> }
>
> char bar()
> {
> v8qi tx = { 100, 0, 0, 0, 0, 0, 0, 0 };
> v8qi ty = { 200, 0, 0, 0, 0, 0, 0, 0 };
> v8qi t = __builtin_ia32_psubusb(tx, ty);
> return t[0];
> }
>
> /* { dg-final { scan-assembler-times "movl\[ \\t\]+\\\$3," 1 } } */
> /* { dg-final { scan-assembler-times "xorl\[ \\t\]+" 1 } } */
> /* { dg-final { scan-assembler-not "psubusb\[ \\t\]+%xmm\[0-9\]+" } } */
