https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127378
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> --- I'd go with 2026-09-17 Jakub Jelinek <[email protected]> Manjunath Matti <[email protected]> PR middle-end/127378 * gimple-lower-bitint.cc (bitint_large_huge::lower_mergeable_stmt): On big endian, compare idx_next in separate_ext loop against bo_idx + total - 1 - end, and if that wraps around, compare idx against 0 instead. * gcc.dg/bitint-145.c: New test. --- a/gcc/gimple-lower-bitint.cc 2026-09-08 22:18:28.493021390 +0200 +++ b/gcc/gimple-lower-bitint.cc 2026-09-17 17:24:10.713167910 +0200 @@ -3271,15 +3271,18 @@ bitint_large_huge::lower_mergeable_stmt bitint_big_endian ? size_int (-1) : size_one_node); insert_before (g); - if (bitint_big_endian && rem != 0) - g = gimple_build_cond (NE_EXPR, idx, - size_int (bo_idx + 1), + /* For big-endian, if bo_idx + total - 1 - end is all ones, then + compare idx (which is equal to idx_next + 1) against 0 + instead. */ + if (bitint_big_endian && bo_idx + total - end == 0) + g = gimple_build_cond (NE_EXPR, idx, size_zero_node, NULL_TREE, NULL_TREE); else g = gimple_build_cond (NE_EXPR, idx_next, size_int (bo_idx + (bitint_big_endian - ? 0 : end)), + ? total - 1 - end + : end)), NULL_TREE, NULL_TREE); insert_before (g); m_gsi = gsi_for_stmt (stmt); --- a/gcc/testsuite/gcc.dg/bitint-145.c 2026-09-17 17:08:34.038519108 +0200 +++ b/gcc/testsuite/gcc.dg/bitint-145.c 2026-09-17 17:08:07.047875025 +0200 @@ -0,0 +1,35 @@ +/* PR middle-end/127378 */ +/* { dg-do run { target bitint } } */ +/* { dg-options "-std=c23 -O2" } */ + +#if __BITINT_MAXWIDTH__ >= 768 +unsigned _BitInt(512) a; +unsigned _BitInt(768) b = -1; + +__attribute__((noipa)) void +foo (unsigned _BitInt(135) *p) +{ + a = (_BitInt(135)) (p[0] + p[1]); +} + +__attribute__((noipa)) void +bar (unsigned _BitInt(200) *p) +{ + b = p[0] + p[1]; +} +#endif + +int +main () +{ +#if __BITINT_MAXWIDTH__ >= 768 + static unsigned _BitInt(135) p[2] = { -1, 0 }; + static unsigned _BitInt(200) q[2] = { 1, 2 }; + foo (p); + if (a != (unsigned _BitInt(512)) -1) + __builtin_abort (); + bar (q); + if (b != 3) + __builtin_abort (); +#endif +} instead. So far tested on cfarm121 with make -j192 -k check-gcc GCC_TEST_RUN_EXPENSIVE=1 RUNTESTFLAGS="GCC_TEST_RUN_EXPENSIVE=1 --target_board=unix\{-m32,-m64\} dg.exp='*bitint* pr112673.c builtin-stdc-bit-*.c pr112566-2.c pr112511.c pr116588.c pr116003.c pr113693.c pr113602.c flex-array-counted-by-7.c' dg-torture.exp='*bitint* pr116480-2.c pr114312.c pr114121.c' dfp.exp=*bitint* vect.exp='vect-early-break_99-pr113287.c' tree-ssa.exp=pr113735.c" where without this patch I see FAIL: gcc.dg/bitint-28.c execution test FAIL: gcc.dg/bitint-29.c execution test FAIL: gcc.dg/bitint-30.c execution test FAIL: gcc.dg/bitint-31.c execution test FAIL: gcc.dg/dfp/bitint-8.c execution test FAIL: gcc.dg/torture/bitint-16.c -O1 execution test FAIL: gcc.dg/torture/bitint-16.c -O2 execution test FAIL: gcc.dg/torture/bitint-16.c -O2 -flto -fno-use-linker-plugin -flto-partition=none execution test FAIL: gcc.dg/torture/bitint-16.c -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects execution test FAIL: gcc.dg/torture/bitint-16.c -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer -finline-functions execution test FAIL: gcc.dg/torture/bitint-16.c -O3 -g execution test FAIL: gcc.dg/torture/bitint-16.c -Os execution test failures and with this patch the bitint-16.c failures are gone. Going to test it on s390x next.
