{"id":2225424,"url":"http://patchwork.ozlabs.org/api/patches/2225424/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/aeboBtP2T1w1r05A@cowardly-lion.the-meissners.org/","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":"","list_archive_url":null,"date":"2026-04-21T02:59:18","name":"GCC 17.0 PowerPC patches V6 [PATCH 2/5]: Add saturate subtract support","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"2b00d63501d60a21d3bb85ecb890032b82aa18a8","submitter":{"id":73991,"url":"http://patchwork.ozlabs.org/api/people/73991/?format=json","name":"Michael Meissner","email":"meissner@linux.ibm.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/aeboBtP2T1w1r05A@cowardly-lion.the-meissners.org/mbox/","series":[{"id":500716,"url":"http://patchwork.ozlabs.org/api/series/500716/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=500716","date":"2026-04-21T02:59:18","name":"GCC 17.0 PowerPC patches V6 [PATCH 2/5]: Add saturate subtract support","version":1,"mbox":"http://patchwork.ozlabs.org/series/500716/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2225424/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2225424/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=ibm.com header.i=@ibm.com header.a=rsa-sha256\n header.s=pp1 header.b=XiJTCwpT;\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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charset=us-ascii","Content-Disposition":"inline","In-Reply-To":"","X-TM-AS-GCONF":"00","X-Proofpoint-Spam-Details-Enc":"AW1haW4tMjYwNDIxMDAyNiBTYWx0ZWRfX+dUpl++07saL\n 3eXflQGditASMhHlGFZm0Us1VulRfH/Dc1yEjH8wjOvSSd8DodEq3YKfUiRB24sH+7qm6txC7Bn\n wbbzaqrGNyreDv862VP6SWITvgvjdul3sECOPJXpTOfEwL+VrgejxW9z+rGSPVy07JcGyyT6Au/\n w095LQLHkLKPLqL2dYllfAi1rkPlGPQDwk6A4vF48LQdjgX6YhxnDmxH0NSPBnMuI85KjhTBDWF\n 8QArC8k+zzPch17s+BpK1ksePbj9p33GEB9hQnPWzkClmyF/5PUtsogEzNpyhBmQhojKG+4dOAx\n R+LfRlZKegBvPM27LTN8Ct7jbunV4jcQSx8AqThxUtcPOocdVRz33yqOcBrvzRrr85MPlmIGijG\n jqGgTCrmNDG8EZaOxLwOPbpWvZk4kNwx/DuXzk4Tb/FLrxByIJ8nia/3RfQhL2JAa7rl2m9lKVG\n 3ISbBObA8pVpSDN0OAA==","X-Proofpoint-GUID":"hwN6N8lYHs0toA-gg0IC3QPBxeC5dtYl","X-Authority-Analysis":"v=2.4 cv=SOJykuvH c=1 sm=1 tr=0 ts=69e6e80c cx=c_pps\n a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17\n a=kj9zAlcOel0A:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22\n a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=mDV3o1hIAAAA:8\n a=VnNF1IyMAAAA:8 a=H_X61Btrdrbtd-VXSpwA:9 a=CjuIK1q_8ugA:10","X-Proofpoint-ORIG-GUID":"hwN6N8lYHs0toA-gg0IC3QPBxeC5dtYl","X-Proofpoint-Virus-Version":"vendor=baseguard\n engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49\n definitions=2026-04-20_05,2026-04-20_02,2025-10-01_01","X-Proofpoint-Spam-Details":"rule=outbound_notspam policy=outbound score=0\n malwarescore=0 spamscore=0 priorityscore=1501 lowpriorityscore=0\n clxscore=1015 phishscore=0 suspectscore=0 adultscore=0 impostorscore=0\n bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound\n adjust=0 reason=mlx scancount=1 engine=8.22.0-2604070000\n definitions=main-2604210026","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":"This patch adds support for saturating subtract instructions that might be added\nto a future PowerPC. I think I had originally submitted patches that added a\nnew built-in function to generate the subfus and subdus instructions. Segher\nsuggested that instead of generating a built-in function, that I should just\nhaving GCC automatically recognize cases where a saturating subtract could be\ngenerated. This patch generates the saturating subtract instructions in the\nappropriate context.\n\nThis patch needs the -mcpu=future patch posted on April 8th, 2026:\n\n * https://gcc.gnu.org/pipermail/gcc-patches/2026-April/712532.html\n\nI have built bootstrap little endian compilers on power10 systems, and\nbig endian compiler on power9 systems. There were no regression in the\ntests. Can I add the patches to the GCC trunk after the -mcpu=future\npatch is applied and GCC 17 has opened up?\n\ngcc/\n\n2026-04-20 Michael Meissner \n\n\t* config/rs6000/rs6000.md (gtu_geu): New code iterator.\n\t(subfus3_): New insns.\n\ngcc/testsuite/\n\n2026-04-16 Michael Meissner \n\n\t* gcc.target/powerpc/saturate-subtract-1.c: New test.\n\t* gcc.target/powerpc/saturate-subtract-2.c: Likewise.\n\t* lib/target-supports.exp (check_effective_target_powerpc_future_ok):\n\tNew target test.\n---\n gcc/config/rs6000/rs6000.md | 14 +++++++\n .../gcc.target/powerpc/saturate-subtract-1.c | 39 ++++++++++++++++++\n .../gcc.target/powerpc/saturate-subtract-2.c | 40 +++++++++++++++++++\n gcc/testsuite/lib/target-supports.exp | 13 ++++++\n 4 files changed, 106 insertions(+)\n create mode 100644 gcc/testsuite/gcc.target/powerpc/saturate-subtract-1.c\n create mode 100644 gcc/testsuite/gcc.target/powerpc/saturate-subtract-2.c","diff":"diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md\nindex 57a239791ee..199a95b84c4 100644\n--- a/gcc/config/rs6000/rs6000.md\n+++ b/gcc/config/rs6000/rs6000.md\n@@ -2397,6 +2397,20 @@ (define_insn_and_split \"*subfsi3_carry_in_xx_64\"\n \"\"\n )\n \n+;; Saturating subtract\n+(define_code_iterator gtu_geu [gtu geu])\n+\n+(define_insn \"*subfus3_\"\n+ [(set (match_operand:GPR 0 \"gpc_reg_operand\" \"=r\")\n+\t(if_then_else:GPR (gtu_geu (match_operand:GPR 1 \"gpc_reg_operand\" \"r\")\n+\t\t\t\t (match_operand:GPR 2 \"gpc_reg_operand\" \"r\"))\n+\t\t\t (minus:GPR (match_dup 1)\n+\t\t\t\t (match_dup 2))\n+\t\t\t (const_int 0)))]\n+ \"TARGET_FUTURE\"\n+ \"subus %0,%1,%2\"\n+ [(set_attr \"type\" \"add\")])\n+\n (define_insn \"@neg2\"\n [(set (match_operand:GPR 0 \"gpc_reg_operand\" \"=r\")\n \t(neg:GPR (match_operand:GPR 1 \"gpc_reg_operand\" \"r\")))]\ndiff --git a/gcc/testsuite/gcc.target/powerpc/saturate-subtract-1.c b/gcc/testsuite/gcc.target/powerpc/saturate-subtract-1.c\nnew file mode 100644\nindex 00000000000..c32a70a5e89\n--- /dev/null\n+++ b/gcc/testsuite/gcc.target/powerpc/saturate-subtract-1.c\n@@ -0,0 +1,39 @@\n+/* { dg-do compile } */\n+/* { dg-options \"-mdejagnu-cpu=future -O2\" } */\n+/* { dg-require-effective-target powerpc_future_ok } */\n+\n+/* Check that saturating subtract (subfus) is generated. Check that all\n+ combinations of >, >=, <, and <= are optimized. */\n+\n+#ifndef TYPE\n+#define TYPE\tunsigned int\n+#endif\n+\n+void\n+saturated_subtract_gt (TYPE a, TYPE b, TYPE *p)\n+{\n+ *p = (a > b) ? a - b : 0;\n+}\n+\n+void\n+saturated_subtract_ge (TYPE a, TYPE b, TYPE *p)\n+{\n+ *p = (a >= b) ? a - b : 0;\n+}\n+\n+void\n+saturated_subtract_lt (TYPE a, TYPE b, TYPE *p)\n+{\n+ *p = (a < b) ? 0 : a - b;\n+}\n+\n+void\n+saturated_subtract_le (TYPE a, TYPE b, TYPE *p)\n+{\n+ *p = (a <= b) ? 0 : a - b;\n+}\n+\n+/* { dg-final { scan-assembler-times {\\msubwus\\M} 4 } } */\n+/* { dg-final { scan-assembler-not {\\mcmplw\\M} } } */\n+/* { dg-final { scan-assembler-not {\\misel\\M} } } */\n+/* { dg-final { scan-assembler-not {\\msubf\\M} } } */\ndiff --git a/gcc/testsuite/gcc.target/powerpc/saturate-subtract-2.c b/gcc/testsuite/gcc.target/powerpc/saturate-subtract-2.c\nnew file mode 100644\nindex 00000000000..482d7384c17\n--- /dev/null\n+++ b/gcc/testsuite/gcc.target/powerpc/saturate-subtract-2.c\n@@ -0,0 +1,40 @@\n+/* { dg-do compile } */\n+/* { dg-require-effective-target powerpc_future_ok } */\n+/* { dg-require-effective-target lp64 } */\n+/* { dg-options \"-mdejagnu-cpu=future -O2\" } */\n+\n+/* Check that saturating subtract (subfus) is generated. Check that all\n+ combinations of >, >=, <, and <= are optimized. */\n+\n+#ifndef TYPE\n+#define TYPE\tunsigned long long\n+#endif\n+\n+void\n+saturated_subtract_gt (TYPE a, TYPE b, TYPE *p)\n+{\n+ *p = (a > b) ? a - b : 0;\n+}\n+\n+void\n+saturated_subtract_ge (TYPE a, TYPE b, TYPE *p)\n+{\n+ *p = (a >= b) ? a - b : 0;\n+}\n+\n+void\n+saturated_subtract_lt (TYPE a, TYPE b, TYPE *p)\n+{\n+ *p = (a < b) ? 0 : a - b;\n+}\n+\n+void\n+saturated_subtract_le (TYPE a, TYPE b, TYPE *p)\n+{\n+ *p = (a <= b) ? 0 : a - b;\n+}\n+\n+/* { dg-final { scan-assembler-times {\\msubdus\\M} 4 } } */\n+/* { dg-final { scan-assembler-not {\\mcmpld\\M} } } */\n+/* { dg-final { scan-assembler-not {\\misel\\M} } } */\n+/* { dg-final { scan-assembler-not {\\msubf\\M} } } */\ndiff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp\nindex 1b9e0bf8f49..0149f6f5c13 100644\n--- a/gcc/testsuite/lib/target-supports.exp\n+++ b/gcc/testsuite/lib/target-supports.exp\n@@ -8194,6 +8194,19 @@ proc check_htm_hw_available { } {\n \t}\n }]\n }\n+\n+# Return 1 if this is a PowerPC target supporting -mcpu=future\n+\n+proc check_effective_target_powerpc_future_ok { } {\n+ return [check_no_compiler_messages powerpc_future_ok object {\n+\tunsigned long a, b, c;\n+\tint main (void) {\n+\t asm (\"subdus %0,%1,%2\" : \"=r\" (a) : \"r\" (b), \"r\" (c));\n+\t return 0;\n+\t}\n+ } \"-mcpu=future\"]\n+}\n+\n # Return 1 if this is a PowerPC target supporting -mcpu=cell.\n \n proc check_effective_target_powerpc_ppu_ok { } {\n","prefixes":[]}