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{ "id": 2228384, "url": "http://patchwork.ozlabs.org/api/patches/2228384/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/patch/20260426111124.19995-1-sergey_v_kaplun@mail.ru/", "project": { "id": 17, "url": "http://patchwork.ozlabs.org/api/projects/17/?format=api", "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": "<20260426111124.19995-1-sergey_v_kaplun@mail.ru>", "list_archive_url": null, "date": "2026-04-26T11:11:24", "name": "[v1] x86_64: Ignore zero-sized arrays in struct in ABI [PR125023]", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "8efd09f196a462563a9d8e0cb8f38fdb60eae319", "submitter": { "id": 93257, "url": "http://patchwork.ozlabs.org/api/people/93257/?format=api", "name": "Sergey Kaplun", "email": "sergey_v_kaplun@mail.ru" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/gcc/patch/20260426111124.19995-1-sergey_v_kaplun@mail.ru/mbox/", "series": [ { "id": 501525, "url": "http://patchwork.ozlabs.org/api/series/501525/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=501525", "date": "2026-04-26T11:11:24", "name": "[v1] x86_64: Ignore zero-sized arrays in struct in ABI [PR125023]", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/501525/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2228384/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2228384/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>", "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": 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<sergey_v_kaplun@mail.ru>", "Subject": "[PATCH v1] x86_64: Ignore zero-sized arrays in struct in ABI\n [PR125023]", "Date": "Sun, 26 Apr 2026 14:11:24 +0300", "Message-ID": "<20260426111124.19995-1-sergey_v_kaplun@mail.ru>", "X-Mailer": "git-send-email 2.52.0", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "X-Mailru-Src": "smtp", "X-7564579A": "646B95376F6C166E", "X-77F55803": "\n 4F1203BC0FB41BD9DA546775E7411B7CE986616F3A3417347DFD4FF2BCFA280700894C459B0CD1B97D12BE10857CFFFA91417EB218679B8297BF961A42FD107A909B6ED457E85EBCB04C393452CF6677", "X-7FA49CB5": "\n 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0D63561A33F958A5B1B398A0A7B9D1EB5002B1117B3ED69625D3870E045E6445886DC9BC01168B20823CB91A9FED034534781492E4B8EEAD4022A62EF65EC23DC79554A2A72441328621D336A7BC284946AD531847A6065A535571D14F44ED41", "X-C8649E89": "\n 1C3962B70DF3F0AD73CAD6646DEDE191716CD42B3DD1D34C77DD89D51EBB774225B6776AC983F447FC0B9F89525902EE6F57B2FD27647F25E66C117BDB76D659993093AF6FE3C9DA3BA15E089C8B6896A34411CA02EE94C6CBE346A7C7DA3D083766A5FA4CAC60AAB8341EE9D5BE9A0AAFA8DE28019AA2BF4CFB380B334D02D73FE81E369918122D8CD93680B12512CF4C41F94D744909CE2512F26BEC029E554B0498F7145B5F5CA37170703DF706BD964550E41902C4E4", "X-D57D3AED": "\n 3ZO7eAau8CL7WIMRKs4sN3D3tLDjz0dLbV79QFUyzQ2Ujvy7cMT6pYYqY16iZVKkSc3dCLJ7zSJH7+u4VD18S7Vl4ZUrpaVfd2+vE6kuoey4m4VkSEu53w8ahmwBjZKM/YPHZyZHvz5uv+WouB9+ObcCpyrx6l7KImUglyhkEat/+ysWwi0gdhEs0JGjl6ggRWTy1haxBpVdbIX1nthFXMZebaIdHP2ghjoIc/363UZI6Kf1ptIMVW+UUD87bVUovXfPNd6MQts=", "X-Mailru-Sender": "\n 583F1D7ACE8F49BDD951BA70C165859E135C226DBB08E6B0ED188C5D0CCD93D425D8F0979836452C24086651E6B4CDF0DE8D183BFE63BE498B67290C0B8F2C0D542E45290E8F34C14AAFE97A8A54CD0C3AE1CD5F6FCBBECB3DDE9B364B0DF289AE208404248635DF", "X-Mras": "Ok", "X-BeenThere": "gcc-patches@gcc.gnu.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Gcc-patches mailing list <gcc-patches.gcc.gnu.org>", "List-Unsubscribe": "<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>", "List-Archive": "<https://gcc.gnu.org/pipermail/gcc-patches/>", "List-Post": "<mailto:gcc-patches@gcc.gnu.org>", "List-Help": "<mailto:gcc-patches-request@gcc.gnu.org?subject=help>", "List-Subscribe": "<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>", "Errors-To": "gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org" }, "content": "In cases when the pass-by-value structure has a multidimensional array\nfield like the following:\n| typedef struct\n| {\n| float x;\n| float hole[0][2][2];\n| float y;\n| } float_hole;\n\nthe structure is passed through the stack. Since sub-array ([2][2]) with\nthe first float field exceeds the 16-byte size to be passed in\nregisters, the total structure is considered to be passed through the\nstack. The current logic doesn't handle the zero-sized arrays (on the\ntop level or in the middle of a multidimensional array).\n\nThis patch skips zero-sized arrays and emits a warning for C and C++ for\npassing by value a struct with a zero-sized array field.\n\n PR target/125023\n * config/i386/i386.cc (classify_argument): Ignore zero-sized\n arrays fields in argument classification to avoid passing a\n structure through the stack. Add the diagnostic message about\n the ABI difference.\n\n * g++.target/i386/pr125023-struct-zero-arr-abi.C: New test.\n * gcc.target/i386/pr125023-struct-zero-arr-abi.c: New test.\n\nSigned-off-by: Sergey Kaplun <sergey_v_kaplun@mail.ru>\n---\n\nThe PR: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125023\n\nTested with on x86_64 Linux comparing with the current master.\n\n| for i in $(find gcc/ -name \"*.sum\");do ../contrib/dg-cmp-results.sh -v -v '*' ../../master/build/$i $i; done\n\nFAIL->PASS: gcc.target/i386/pr125023-struct-zero-arr-abi.c scan-assembler movdqa\nFAIL->PASS: gcc.target/i386/pr125023-struct-zero-arr-abi.c scan-assembler-not rsp\nFAIL->PASS: gcc.target/i386/pr125023-struct-zero-arr-abi.c (test for warnings, line 13)\n\n<snipped>\n\nFAIL->PASS: g++.target/i386/pr125023-struct-zero-arr-abi.C -std=gnu++20 scan-assembler movdqa\nFAIL->PASS: g++.target/i386/pr125023-struct-zero-arr-abi.C -std=gnu++20 scan-assembler-not rsp\nFAIL->PASS: g++.target/i386/pr125023-struct-zero-arr-abi.C -std=gnu++20 (test for warnings, line 13)\nFAIL->PASS: g++.target/i386/pr125023-struct-zero-arr-abi.C -std=gnu++26 scan-assembler movdqa\nFAIL->PASS: g++.target/i386/pr125023-struct-zero-arr-abi.C -std=gnu++26 scan-assembler-not rsp\nFAIL->PASS: g++.target/i386/pr125023-struct-zero-arr-abi.C -std=gnu++26 (test for warnings, line 13)\nFAIL->PASS: g++.target/i386/pr125023-struct-zero-arr-abi.C -std=gnu++98 scan-assembler movdqa\nFAIL->PASS: g++.target/i386/pr125023-struct-zero-arr-abi.C -std=gnu++98 scan-assembler-not rsp\nFAIL->PASS: g++.target/i386/pr125023-struct-zero-arr-abi.C -std=gnu++98 (test for warnings, line 13)\n\n gcc/config/i386/i386.cc | 17 ++++++++++++++++\n .../i386/pr125023-struct-zero-arr-abi.C | 20 +++++++++++++++++++\n .../i386/pr125023-struct-zero-arr-abi.c | 20 +++++++++++++++++++\n 3 files changed, 57 insertions(+)\n create mode 100644 gcc/testsuite/g++.target/i386/pr125023-struct-zero-arr-abi.C\n create mode 100644 gcc/testsuite/gcc.target/i386/pr125023-struct-zero-arr-abi.c", "diff": "diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc\nindex 4249c55ce6e..c3d5d397c0f 100644\n--- a/gcc/config/i386/i386.cc\n+++ b/gcc/config/i386/i386.cc\n@@ -2356,6 +2356,23 @@ classify_argument (machine_mode mode, const_tree type,\n \t\t\t }\n \t\t\t continue;\n \t\t\t}\n+\t\t /* Skip zero-sized arrays. */\n+\t\t else if (TYPE_MODE (type) == BLKmode\n+\t\t\t && TREE_CODE (type) == ARRAY_TYPE\n+\t\t\t && int_size_in_bytes (type) == 0)\n+\t\t\t{\n+\t\t\t static bool warned;\n+\n+\t\t\t if (!warned && warn_psabi)\n+\t\t\t {\n+\t\t\t warned = true;\n+\t\t\t inform (input_location,\n+\t\t\t\t \"the ABI of passing struct with\"\n+\t\t\t\t \" a zero-sized array member has\"\n+\t\t\t\t \" changed in GCC 16.1\");\n+\t\t\t }\n+\t\t\t continue;\n+\t\t\t}\n \t\t num = classify_argument (TYPE_MODE (type), type,\n \t\t\t\t\t subclasses,\n \t\t\t\t\t (int_bit_position (field)\ndiff --git a/gcc/testsuite/g++.target/i386/pr125023-struct-zero-arr-abi.C b/gcc/testsuite/g++.target/i386/pr125023-struct-zero-arr-abi.C\nnew file mode 100644\nindex 00000000000..f94a798d100\n--- /dev/null\n+++ b/gcc/testsuite/g++.target/i386/pr125023-struct-zero-arr-abi.C\n@@ -0,0 +1,20 @@\n+// PR target/125023\n+// { dg-do compile }\n+// { dg-options \"-O1 -msse\" }\n+\n+typedef struct\n+{\n+ float x;\n+ float hole[0][2][2];\n+ float y;\n+} float_hole;\n+\n+float\n+sum (float_hole h) // { dg-message \"the ABI of passing struct with a zero-sized array member has changed in GCC 16.1\" }\n+{\n+ return h.x + h.y;\n+}\n+\n+// Check that pass-by-value structure is placed in registers, not on stack.\n+// { dg-final { scan-assembler-not \"rsp\" } }\n+// { dg-final { scan-assembler \"movdqa\" } }\ndiff --git a/gcc/testsuite/gcc.target/i386/pr125023-struct-zero-arr-abi.c b/gcc/testsuite/gcc.target/i386/pr125023-struct-zero-arr-abi.c\nnew file mode 100644\nindex 00000000000..a69edd53568\n--- /dev/null\n+++ b/gcc/testsuite/gcc.target/i386/pr125023-struct-zero-arr-abi.c\n@@ -0,0 +1,20 @@\n+/* PR target/125023 */\n+/* { dg-do compile } */\n+/* { dg-options \"-O1 -msse\" } */\n+\n+typedef struct\n+{\n+ float x;\n+ float hole[0][2][2];\n+ float y;\n+} float_hole;\n+\n+float\n+sum (float_hole h) /* { dg-message \"the ABI of passing struct with a zero-sized array member has changed in GCC 16.1\" } */\n+{\n+ return h.x + h.y;\n+}\n+\n+/* Check that pass-by-value structure is placed in registers, not on stack. */\n+/* { dg-final { scan-assembler-not \"rsp\" } } */\n+/* { dg-final { scan-assembler \"movdqa\" } } */\n", "prefixes": [ "v1" ] }