https://gcc.gnu.org/g:500d82452bdba0de71dae1056ccf366fa07147e9
commit r17-3142-g500d82452bdba0de71dae1056ccf366fa07147e9 Author: Jakub Jelinek <[email protected]> Date: Fri Aug 7 21:20:35 2026 +0200 gimple-range-op: Use widen method even for sqrt reverse op [PR126534] For glibc the target hook returns 0 for sqrt precision (i.e. 0.5ulp precise), but we didn't apply the +-0.5ulp widening when doing reverse op and so still came up with a wrong range, even with 0.5ulp precision certain values around 25.0 result in sqrt (x) being 5.0. Even if the hook returns non-zero, I'd say more reasonable handling of it is that it is say worst case 1ulp (or 2ulps etc.) from the correct result (i.e. half ulp precise), rather than just 1ulp from mathematically exact result. So, the following patch uses the newly added widen method to add this 0.5ulp before we feed it into frange_arithmetic. 2026-08-07 Jakub Jelinek <[email protected]> PR tree-optimization/126534 * gimple-range-op.cc (cfn_sqrt::op1_range): Widen lb or ub by further 0.5ulp or 1ulp before squaring it. * gcc.dg/pr126534.c: New test. Reviewed-by: Aldy Hernandez <[email protected]> Diff: --- gcc/gimple-range-op.cc | 10 +++++++-- gcc/testsuite/gcc.dg/pr126534.c | 45 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 53 insertions(+), 2 deletions(-) diff --git a/gcc/gimple-range-op.cc b/gcc/gimple-range-op.cc index da8feda22567..9be143f85cd1 100644 --- a/gcc/gimple-range-op.cc +++ b/gcc/gimple-range-op.cc @@ -573,7 +573,10 @@ public: frange_nextafter (TYPE_MODE (type), lb, dconstninf); if (real_less (&dconst0, &lb)) { - REAL_VALUE_TYPE op = lb; + frange wlhs (type, lb, dconstinf); + wlhs.clear_nan (); + wlhs.widen (type); + REAL_VALUE_TYPE op = wlhs.lower_bound (); frange_arithmetic (MULT_EXPR, type, lb, op, op, dconstninf); } else @@ -587,7 +590,10 @@ public: frange_nextafter (TYPE_MODE (type), ub, dconstinf); if (real_isfinite (&ub)) { - REAL_VALUE_TYPE op = ub; + frange wlhs (type, dconstninf, ub); + wlhs.clear_nan (); + wlhs.widen (type); + REAL_VALUE_TYPE op = wlhs.upper_bound (); frange_arithmetic (MULT_EXPR, type, ub, op, op, dconstinf); } else diff --git a/gcc/testsuite/gcc.dg/pr126534.c b/gcc/testsuite/gcc.dg/pr126534.c new file mode 100644 index 000000000000..4ffb49a8d6ad --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr126534.c @@ -0,0 +1,45 @@ +/* PR tree-optimization/126534 */ +/* { dg-do run } */ +/* { dg-options "-O2" } */ + +[[gnu::noipa]] int +foo (double x) +{ + double y = __builtin_sqrt (x); + if (y <= 5.0) + { + if (x > 25.0) + return 1; + return 2; + } + return 3; +} + +[[gnu::noipa]] int +bar (double x) +{ + double y = __builtin_sqrt (x); + if (y >= 5.0) + { + if (x < 25.0) + return 1; + return 2; + } + return 3; +} + +int +main () +{ +#if __DBL_MANT_DIG__ == 53 && __DBL_MAX_EXP__ == 1024 && __FLT_EVAL_METHOD__ == 0 + volatile double x = 0x1.9000000000001p+4; + volatile double y = 0x1.8ffffffffffffp+4; + if (__builtin_sqrt (x) == 5.0 && __builtin_sqrt (y) == 5.0) + { + if (foo (0x1.9000000000001p+4) != 1) /* 25.000000000000004 */ + __builtin_abort (); + if (bar (0x1.8ffffffffffffp+4) != 1) /* 24.999999999999996 */ + __builtin_abort (); + } +#endif +}
