{"id":2232261,"url":"http://patchwork.ozlabs.org/api/patches/2232261/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/20260504065508.399252-1-herumi@nifty.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null,"list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260504065508.399252-1-herumi@nifty.com>","list_archive_url":null,"date":"2026-05-04T06:55:08","name":"[v4,3/3] i386: Add peephole2 to convert highpart mul to mulx","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"eebc4ffc02b163d5e5507e5bfa4fc1c842b2ac9d","submitter":{"id":92964,"url":"http://patchwork.ozlabs.org/api/people/92964/?format=json","name":null,"email":"herumi@nifty.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/20260504065508.399252-1-herumi@nifty.com/mbox/","series":[{"id":502615,"url":"http://patchwork.ozlabs.org/api/series/502615/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=502615","date":"2026-05-04T06:55:08","name":null,"version":4,"mbox":"http://patchwork.ozlabs.org/series/502615/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2232261/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2232261/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=nifty.com header.i=@nifty.com header.a=rsa-sha256\n header.s=default-1th84yt82rvi header.b=CrHoixxf;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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server2.sourceware.org","From":"herumi@nifty.com","To":"gcc-patches@gcc.gnu.org","Cc":"MITSUNARI Shigeo ","Subject":"[PATCH v4 3/3] i386: Add peephole2 to convert highpart mul to mulx","Date":"Mon, 4 May 2026 15:55:08 +0900","Message-ID":"<20260504065508.399252-1-herumi@nifty.com>","X-Mailer":"git-send-email 2.43.0","In-Reply-To":"\n ","References":"\n ","MIME-Version":"1.0","Content-Transfer-Encoding":"8bit","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com;\n s=default-1th84yt82rvi; t=1777877720;\n bh=GThbQ65werV71DibGXC47jjoeE+ENXK6XNbNw4USuQ4=;\n h=From:To:Cc:Subject:Date:In-Reply-To:References;\n b=CrHoixxf1i9mpfv+6rCK9OqoACjHH0XqchaaJPHYCyH2c66Vis35QRSPVz3eY889qVALCEhi\n hqnuuVLLhwRfugtagMvelPLbwq2MSP2h6jUvIaxLNYVJU44FtNft2wJRh0FRJj3sOkUebD+8l8\n 7Poqjr5i9xBwTS84zKOb0EJdNgx9qu5qUCG1tfyT+Owf21cqgniuHdc8xpqAiuWMw7FCxUfa9b\n zAfgqYV8eZWg1MFIb9IokXBl2wM/w5Vp5GyclekrJitT3YwoEeN3cm85ahyl/lm9gfrbHpCk8A\n EVrhP0QNizUhJhy7xjFbeXhJLvcOkhJf7LfBvtBdEOrADmmQ==","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"From: MITSUNARI Shigeo \n\nWhen the register allocator selects the MUL-based highpart pattern\n(umuldi3_highpart) with the source value already in %rdx, it inserts\na redundant mov to %rax before the mul instruction. Add a peephole2\nthat detects this mov + mul sequence and converts it to a single mulx,\neliminating the extra mov.\n\nThis improves inlined loops that perform multiple unsigned divisions\nby constants. For example, a loop with three div-by-constant\noperations now generates 15 instructions (matching LLVM) instead\nof 18.\n\nBefore (loop body excerpt):\n\tmov\trax, rdx\n\tmul\tr9\n\nAfter:\n\tmulx\trdx, rax, r9\n\ngcc/ChangeLog:\n\n\t* config/i386/i386.md: Add peephole2 to convert\n\tmov + umul_highpart to mulx on BMI2 targets.\n\ngcc/testsuite/ChangeLog:\n\n * gcc.target/i386/bmi2-mulx-highpart-2.c: New test.\n---\n gcc/config/i386/i386.md | 17 +++++++++++++++++\n .../gcc.target/i386/bmi2-mulx-highpart-2.c | 19 +++++++++++++++++++\n 2 files changed, 36 insertions(+)\n create mode 100644 gcc/testsuite/gcc.target/i386/bmi2-mulx-highpart-2.c","diff":"diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md\nindex 472f9d41332..1c394690b04 100644\n--- a/gcc/config/i386/i386.md\n+++ b/gcc/config/i386/i386.md\n@@ -11522,6 +11522,23 @@\n (set_attr \"prefix\" \"vex\")\n (set_attr \"mode\" \"\")])\n \n+;; Convert mov + highpart mul to mulx when the mov source is %rdx.\n+;; mov %rdx, %rax; mulq %src -> mulx %src, %rax, %out\n+(define_peephole2\n+ [(set (match_operand:DWIH 0 \"register_operand\")\n+\t(match_operand:DWIH 1 \"register_operand\"))\n+ (parallel [(set (match_operand:DWIH 2 \"register_operand\")\n+\t\t (umul_highpart:DWIH (match_dup 0)\n+\t\t\t(match_operand:DWIH 3 \"nonimmediate_operand\")))\n+\t (clobber (match_dup 0))\n+\t (clobber (reg:CC FLAGS_REG))])]\n+ \"TARGET_BMI2\n+ && REGNO (operands[1]) == DX_REG\n+ && REGNO (operands[0]) != REGNO (operands[2])\"\n+ [(parallel [(set (match_dup 2)\n+\t\t (umul_highpart:DWIH (match_dup 1) (match_dup 3)))\n+\t (clobber (match_dup 0))])])\n+\n ;; Highpart multiplication patterns\n (define_insn \"mul3_highpart\"\n [(set (match_operand:DWIH 0 \"register_operand\" \"=d\")\ndiff --git a/gcc/testsuite/gcc.target/i386/bmi2-mulx-highpart-2.c b/gcc/testsuite/gcc.target/i386/bmi2-mulx-highpart-2.c\nnew file mode 100644\nindex 00000000000..be56cf15d07\n--- /dev/null\n+++ b/gcc/testsuite/gcc.target/i386/bmi2-mulx-highpart-2.c\n@@ -0,0 +1,19 @@\n+/* { dg-do compile { target { ! ia32 } } } */\n+/* { dg-options \"-O2 -mbmi2\" } */\n+/* { dg-final { check-function-bodies \"**\" \"\" \"\" { target *-*-linux* *-*-gnu* } } } */\n+\n+/*\n+**div7loop:\n+**...\n+**\tmulx\t%rsi, %rax, %rdx\n+**...\n+*/\n+\n+unsigned int\n+div7loop (unsigned int x)\n+{\n+ for (int i = 0; i < 10000; i++) {\n+ x ^= (i ^ x) / 7;\n+ }\n+ return x;\n+}\n","prefixes":["v4","3/3"]}