{"id":2221617,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2221617/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/b7d9dcdd-6638-4e12-8580-89696c06fd90@gmail.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/1.1/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},"msgid":"","date":"2026-04-10T00:52:46","name":"[fortran] Fix Bug 94978 - [13/14/15/16 Regression] Bogus warning \"Array reference at (1) out of bounds ...\"","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"6d8950ae4368a500ce1e1677d142414e64131e93","submitter":{"id":78264,"url":"http://patchwork.ozlabs.org/api/1.1/people/78264/?format=json","name":"Jerry D","email":"jvdelisle2@gmail.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/b7d9dcdd-6638-4e12-8580-89696c06fd90@gmail.com/mbox/","series":[{"id":499374,"url":"http://patchwork.ozlabs.org/api/1.1/series/499374/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=499374","date":"2026-04-10T00:52:46","name":"[fortran] Fix Bug 94978 - [13/14/15/16 Regression] Bogus warning \"Array reference at (1) out of bounds ...\"","version":1,"mbox":"http://patchwork.ozlabs.org/series/499374/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2221617/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2221617/checks/","tags":{},"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=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=UsiIZp7B;\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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boundary=\"------------cWDi5lzKEf00OHHDaALvKp2c\"","Message-ID":"","Date":"Thu, 9 Apr 2026 17:52:46 -0700","MIME-Version":"1.0","User-Agent":"Mozilla Thunderbird","Content-Language":"en-US","To":"gfortran , gcc-patches ","Cc":"Harald Anlauf , Thomas Koenig ,\n Paul Richard Thomas ","From":"Jerry D ","Subject":"[PATCH,fortran] Fix Bug 94978 - [13/14/15/16 Regression] Bogus\n warning \"Array reference at (1) out of bounds ...\"","Autocrypt":"addr=jvdelisle2@gmail.com; keydata=\n xjMEY5TlkxYJKwYBBAHaRw8BAQdAyrkRDhmJhSTTlV/50gJLlvliU6/Lm5C9ViKV8T9y1GnN\n HkplcnJ5IEQgPGp2ZGVsaXNsZTJAZ21haWwuY29tPsKJBBMWCAAxFiEEOFR0TS0390uh8dRV\n uWXAJaWpwWoFAmOU5ZMCGwMECwkIBwUVCAkKCwUWAgMBAAAKCRC5ZcAlpanBalsJAP4wdCiH\n 2Of9oZv1QWgZ/AVdbWFM3Fv47/WZQHOXfoZ9HgD6AkXrKeJ+6usST7PEaDJjptaViT1fLiYY\n V/6XaOKSsgLOOARjlOWTEgorBgEEAZdVAQUBAQdAdA7PczYnl07vnOT9oP/wvvMDd4HP09Zl\n g3LzwXQJWT8DAQgHwngEGBYIACAWIQQ4VHRNLTf3S6Hx1FW5ZcAlpanBagUCY5TlkwIbDAAK\n CRC5ZcAlpanBasF/AQCa5WjlsVpLsEiggZyT18MOJNAdeRd7wkGDUrwedHrvawD/cE1H+/Ms\n L1ZwvQiLfGdx8crigQqWTQyos4kH8Wx82wc=","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":"Hi all,\n\nThe attached patch avoids the bogus warning. I completed regression testing on \nx86_64.\n\nI would appreciate others to take a look.\n\nOK to commit on mainline?\n\nRegards,\n\nJerry\n---\n\nfortran: Avoid bogus do-subscript warnings in skipped inner\n loops [PR94978]\n\nDo not warn from an outer-loop bound substitution when a nested inner loop may\nbe zero-trip after that substitution, because the guarded array reference may\nthen be unreachable.\n\ngcc/fortran/ChangeLog:\n\n\tPR fortran/94978\n\t* frontend-passes.cc (evaluate_loop_bound): New helper.\n\t(inner_loop_may_be_skipped): New helper.\n\t(do_subscript): Skip outer-loop bound warnings when nested inner loops\n\tmay be zero-trip for the substituted bound.\n\ngcc/testsuite/ChangeLog:\n\n\tPR fortran/94978\n\t* gfortran.dg/pr94978.f90: New test.\n\nSigned-off-by: Christopher Albert ","diff":"From f87d2443e27cafde0de1923cd186be92f9cef2a0 Mon Sep 17 00:00:00 2001\nFrom: Christopher Albert \nDate: Sat, 28 Mar 2026 17:26:05 +0100\nSubject: [PATCH] fortran: Avoid bogus do-subscript warnings in skipped inner\n loops [PR94978]\n\nDo not warn from an outer-loop bound substitution when a nested inner loop may\nbe zero-trip after that substitution, because the guarded array reference may\nthen be unreachable.\n\ngcc/fortran/ChangeLog:\n\n\tPR fortran/94978\n\t* frontend-passes.cc (evaluate_loop_bound): New helper.\n\t(inner_loop_may_be_skipped): New helper.\n\t(do_subscript): Skip outer-loop bound warnings when nested inner loops\n\tmay be zero-trip for the substituted bound.\n\ngcc/testsuite/ChangeLog:\n\n\tPR fortran/94978\n\t* gfortran.dg/pr94978.f90: New test.\n\nSigned-off-by: Christopher Albert \n---\n gcc/fortran/frontend-passes.cc | 69 ++++++++++++++++++++++++++-\n gcc/testsuite/gfortran.dg/pr94978.f90 | 24 ++++++++++\n 2 files changed, 91 insertions(+), 2 deletions(-)\n create mode 100644 gcc/testsuite/gfortran.dg/pr94978.f90\n\ndiff --git a/gcc/fortran/frontend-passes.cc b/gcc/fortran/frontend-passes.cc\nindex 56d8e21b9f4..fa508794e20 100644\n--- a/gcc/fortran/frontend-passes.cc\n+++ b/gcc/fortran/frontend-passes.cc\n@@ -2746,6 +2746,66 @@ insert_index (gfc_expr *e, gfc_symbol *sym, mpz_t val, mpz_t ret)\n \n }\n \n+static bool\n+evaluate_loop_bound (gfc_expr *e, gfc_symbol *sym, mpz_t val, mpz_t ret)\n+{\n+ if (e->expr_type == EXPR_CONSTANT)\n+ {\n+ mpz_init_set (ret, e->value.integer);\n+ return true;\n+ }\n+\n+ return insert_index (e, sym, val, ret);\n+}\n+\n+/* Return true if any loop nested inside LOOP_INDEX is not provably entered\n+ after substituting OUTER_VAL for OUTER_SYM. In that case the guarded array\n+ reference may never be evaluated, so do not warn from the outer loop alone. */\n+\n+static bool\n+inner_loop_may_be_skipped (int loop_index, gfc_symbol *outer_sym, mpz_t outer_val)\n+{\n+ int k;\n+ do_t *lp;\n+\n+ FOR_EACH_VEC_ELT_FROM (doloop_list, k, lp, loop_index + 1)\n+ {\n+ gfc_code *loop = lp->c;\n+ int sgn, cmp;\n+ mpz_t do_start, do_end, do_step;\n+\n+ if (loop == NULL || loop->ext.iterator == NULL || loop->ext.iterator->var == NULL)\n+\treturn true;\n+\n+ if (!evaluate_loop_bound (loop->ext.iterator->step, outer_sym, outer_val, do_step))\n+\treturn true;\n+\n+ sgn = mpz_cmp_ui (do_step, 0);\n+ if (sgn == 0)\n+\t{\n+\t mpz_clear (do_step);\n+\t return true;\n+\t}\n+\n+ if (!evaluate_loop_bound (loop->ext.iterator->start, outer_sym, outer_val, do_start)\n+\t || !evaluate_loop_bound (loop->ext.iterator->end, outer_sym, outer_val, do_end))\n+\t{\n+\t mpz_clear (do_step);\n+\t return true;\n+\t}\n+\n+ cmp = mpz_cmp (do_end, do_start);\n+ mpz_clear (do_start);\n+ mpz_clear (do_end);\n+ mpz_clear (do_step);\n+\n+ if ((sgn > 0 && cmp < 0) || (sgn < 0 && cmp > 0))\n+\treturn true;\n+ }\n+\n+ return false;\n+}\n+\n /* Check array subscripts for possible out-of-bounds accesses in DO\n loops with constant bounds. */\n \n@@ -2880,10 +2940,15 @@ do_subscript (gfc_expr **e)\n \t\t mpz_clear (rem);\n \t\t}\n \n+\t bool skip_start = have_do_start\n+\t\t\t\t&& inner_loop_may_be_skipped (j, do_sym, do_start);\n+\t bool skip_end = have_do_end\n+\t\t\t && inner_loop_may_be_skipped (j, do_sym, do_end);\n+\n \t for (i = 0; i< ar->dimen; i++)\n \t\t{\n \t\t mpz_t val;\n-\t\t if (ar->dimen_type[i] == DIMEN_ELEMENT && have_do_start\n+\t\t if (ar->dimen_type[i] == DIMEN_ELEMENT && have_do_start && !skip_start\n \t\t && insert_index (ar->start[i], do_sym, do_start, val))\n \t\t {\n \t\t if (ar->as->lower[i]\n@@ -2909,7 +2974,7 @@ do_subscript (gfc_expr **e)\n \t\t mpz_clear (val);\n \t\t }\n \n-\t\t if (ar->dimen_type[i] == DIMEN_ELEMENT && have_do_end\n+\t\t if (ar->dimen_type[i] == DIMEN_ELEMENT && have_do_end && !skip_end\n \t\t && insert_index (ar->start[i], do_sym, do_end, val))\n \t\t {\n \t\t if (ar->as->lower[i]\ndiff --git a/gcc/testsuite/gfortran.dg/pr94978.f90 b/gcc/testsuite/gfortran.dg/pr94978.f90\nnew file mode 100644\nindex 00000000000..5d64d227fdc\n--- /dev/null\n+++ b/gcc/testsuite/gfortran.dg/pr94978.f90\n@@ -0,0 +1,24 @@\n+! { dg-do compile }\n+! { dg-options \"-Wdo-subscript\" }\n+\n+implicit none\n+\n+integer(4) :: i, j\n+integer(4) :: pascal(0:8, 0:8)\n+\n+do i = 0, 8\n+ pascal(i, 0) = 1\n+ do j = 1, i - 1\n+ pascal(i, j) = pascal(i - 1, j) + pascal(i - 1, j - 1) ! { dg-bogus \"Array reference at \\\\(1\\\\) out of bounds\" }\n+ end do\n+ do j = i, 8\n+ pascal(i, j) = 0\n+ end do\n+ pascal(i, i) = 1\n+end do\n+\n+do i = 0, 8\n+ print '(9I4)', pascal(i, :)\n+end do\n+\n+end\n-- \n2.53.0\n\n","prefixes":["fortran"]}