From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by sourceware.org (Postfix) with ESMTP id EE905385694C for ; Thu, 16 Jun 2022 16:10:01 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org EE905385694C Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9DCCA12FC; Thu, 16 Jun 2022 09:10:01 -0700 (PDT) Received: from localhost (e121540-lin.manchester.arm.com [10.32.98.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8F0503F73B; Thu, 16 Jun 2022 09:10:00 -0700 (PDT) From: Richard Sandiford To: Tamar Christina Mail-Followup-To: Tamar Christina , gcc-patches@gcc.gnu.org, nd@arm.com, Richard.Earnshaw@arm.com, Marcus.Shawcroft@arm.com, Kyrylo.Tkachov@arm.com, richard.sandiford@arm.com Cc: gcc-patches@gcc.gnu.org, nd@arm.com, Richard.Earnshaw@arm.com, Marcus.Shawcroft@arm.com, Kyrylo.Tkachov@arm.com Subject: Re: [PATCH 1/2]AArch64 Add fallback case using sdot for usdot References: Date: Thu, 16 Jun 2022 17:09:59 +0100 In-Reply-To: (Tamar Christina's message of "Thu, 16 Jun 2022 11:48:44 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Spam-Status: No, score=-57.8 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_NONE, KAM_DMARC_STATUS, KAM_LAZY_DOMAIN_SECURITY, KAM_SHORT, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 16 Jun 2022 16:10:04 -0000 Tamar Christina writes: > Hi All, > > The usdot operation is common in video encoder and decoders including some of > the most widely used ones. > > This patch adds a +dotprod version of the optab as a fallback for when you do > have sdot but not usdot available. > > The fallback works by adding a bias to the unsigned argument to convert it to > a signed value and then correcting for the bias later on. > > Essentially it relies on (x - 128)y + 128y == xy where x is unsigned and y is > signed (assuming both are 8-bit values). Because the range of a signed byte is > only to 127 we split the bias correction into: > > (x - 128)y + 127y + y I bet you knew this question was coming, but: this technique isn't target-specific, so wouldn't it be better to handle it in tree-vect-patterns.cc instead? Thanks, Richard > Concretely for: > > #define N 480 > #define SIGNEDNESS_1 unsigned > #define SIGNEDNESS_2 signed > #define SIGNEDNESS_3 signed > #define SIGNEDNESS_4 unsigned > > SIGNEDNESS_1 int __attribute__ ((noipa)) > f (SIGNEDNESS_1 int res, SIGNEDNESS_3 char *restrict a, > SIGNEDNESS_4 char *restrict b) > { > for (__INTPTR_TYPE__ i = 0; i < N; ++i) > { > int av = a[i]; > int bv = b[i]; > SIGNEDNESS_2 short mult = av * bv; > res += mult; > } > return res; > } > > we generate: > > movi v5.16b, 0x7f > mov x3, 0 > movi v4.16b, 0x1 > movi v3.16b, 0xffffffffffffff80 > movi v0.4s, 0 > .L2: > ldr q2, [x2, x3] > ldr q1, [x1, x3] > add x3, x3, 16 > sub v2.16b, v2.16b, v3.16b > sdot v0.4s, v2.16b, v1.16b > sdot v0.4s, v5.16b, v1.16b > sdot v0.4s, v4.16b, v1.16b > cmp x3, 480 > bne .L2 > > instead of: > > movi v0.4s, 0 > mov x3, 0 > .L2: > ldr q2, [x1, x3] > ldr q1, [x2, x3] > add x3, x3, 16 > sxtl v4.8h, v2.8b > sxtl2 v3.8h, v2.16b > uxtl v2.8h, v1.8b > uxtl2 v1.8h, v1.16b > mul v2.8h, v2.8h, v4.8h > mul v1.8h, v1.8h, v3.8h > saddw v0.4s, v0.4s, v2.4h > saddw2 v0.4s, v0.4s, v2.8h > saddw v0.4s, v0.4s, v1.4h > saddw2 v0.4s, v0.4s, v1.8h > cmp x3, 480 > bne .L2 > > The new sequence is significantly faster as the operations it uses are well > optimized. Note that execution tests are already in the mid-end testsuite. > > Thanks to James Greenhalgh for the tip-off. > > Bootstrapped Regtested on aarch64-none-linux-gnu and no issues. > > Ok for master? > > Thanks, > Tamar > > gcc/ChangeLog: > > * config/aarch64/aarch64-simd.md (usdot_prod): Generate fallback > or call original isns ... > (usdot_prod_insn): ...here. > > gcc/testsuite/ChangeLog: > > * gcc.target/aarch64/simd/vusdot-autovec-2.c: New test. > > --- inline copy of patch -- > diff --git a/gcc/config/aarch64/aarch64-simd.md b/gcc/config/aarch64/aarch64-simd.md > index cf2f4badacc594df9ecf06de3f8ea570ef9e0ff2..235a6fa371e471816284e3383e8564e9cf643a74 100644 > --- a/gcc/config/aarch64/aarch64-simd.md > +++ b/gcc/config/aarch64/aarch64-simd.md > @@ -623,7 +623,7 @@ (define_insn "dot_prod" > > ;; These instructions map to the __builtins for the Armv8.6-a I8MM usdot > ;; (vector) Dot Product operation and the vectorized optab. > -(define_insn "usdot_prod" > +(define_insn "usdot_prod_insn" > [(set (match_operand:VS 0 "register_operand" "=w") > (plus:VS > (unspec:VS [(match_operand: 1 "register_operand" "w") > @@ -635,6 +635,43 @@ (define_insn "usdot_prod" > [(set_attr "type" "neon_dot")] > ) > > +;; usdot auto-vec fallback code > +(define_expand "usdot_prod" > + [(set (match_operand:VS 0 "register_operand") > + (plus:VS > + (unspec:VS [(match_operand: 1 "register_operand") > + (match_operand: 2 "register_operand")] > + UNSPEC_USDOT) > + (match_operand:VS 3 "register_operand")))] > + "TARGET_DOTPROD || TARGET_I8MM" > +{ > + if (TARGET_I8MM) > + { > + emit_insn (gen_usdot_prod_insn (operands[0], operands[1], > + operands[2], operands[3])); > + DONE; > + } > + > + machine_mode elemmode = GET_MODE_INNER (mode); > + HOST_WIDE_INT val = 1 << (GET_MODE_BITSIZE (elemmode).to_constant () - 1); > + rtx signbit = gen_int_mode (val, elemmode); > + rtx t1 = gen_reg_rtx (mode); > + rtx t2 = gen_reg_rtx (mode); > + rtx tmp = gen_reg_rtx (mode); > + rtx c1 = gen_const_vec_duplicate (mode, > + gen_int_mode (val - 1, elemmode)); > + rtx c2 = gen_const_vec_duplicate (mode, gen_int_mode (1, elemmode)); > + rtx dup = gen_const_vec_duplicate (mode, signbit); > + c1 = force_reg (mode, c1); > + c2 = force_reg (mode, c2); > + dup = force_reg (mode, dup); > + emit_insn (gen_sub3 (tmp, operands[1], dup)); > + emit_insn (gen_sdot_prod (t1, tmp, operands[2], operands[3])); > + emit_insn (gen_sdot_prod (t2, c1, operands[2], t1)); > + emit_insn (gen_sdot_prod (operands[0], c2, operands[2], t2)); > + DONE; > +}) > + > ;; These instructions map to the __builtins for the Dot Product > ;; indexed operations. > (define_insn "aarch64_dot_lane" > diff --git a/gcc/testsuite/gcc.target/aarch64/simd/vusdot-autovec-2.c b/gcc/testsuite/gcc.target/aarch64/simd/vusdot-autovec-2.c > new file mode 100644 > index 0000000000000000000000000000000000000000..acd8e36209690386d021df72f1467a696750ac3e > --- /dev/null > +++ b/gcc/testsuite/gcc.target/aarch64/simd/vusdot-autovec-2.c > @@ -0,0 +1,25 @@ > +/* { dg-do compile } */ > +/* { dg-options "-O3 -march=armv8.2-a+noi8mm+dotprod" } */ > + > +#define N 480 > +#define SIGNEDNESS_1 unsigned > +#define SIGNEDNESS_2 signed > +#define SIGNEDNESS_3 signed > +#define SIGNEDNESS_4 unsigned > + > +SIGNEDNESS_1 int __attribute__ ((noipa)) > +f (SIGNEDNESS_1 int res, SIGNEDNESS_3 char *restrict a, > + SIGNEDNESS_4 char *restrict b) > +{ > + for (__INTPTR_TYPE__ i = 0; i < N; ++i) > + { > + int av = a[i]; > + int bv = b[i]; > + SIGNEDNESS_2 short mult = av * bv; > + res += mult; > + } > + return res; > +} > + > +/* { dg-final { scan-assembler-not {\tusdot\t} } } */ > +/* { dg-final { scan-assembler-times {\tsdot\t} 3 } } */