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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/113774] wrong code with _BitInt() arithmetics at -O2 Date: Wed, 07 Feb 2024 20:24:45 +0000 [thread overview] Message-ID: <bug-113774-4-xR6dCDRyZ5@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-113774-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113774 --- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- unsigned long long a[32], b[32], v[32], r[32]; void foo (unsigned int n) { unsigned long long c = 0; for (unsigned long i = 0; i < n; i += 2) { unsigned long j = i + 1; b[i] = __builtin_addcll (b[i], v[i], c, &c); b[j] = __builtin_addcll (b[j], v[j], c, &c); } b[4] = __builtin_addcll (b[4] & 1, v[4] & 1, c, &c) & 1; c = 0; for (unsigned long i = 0; i < n; i += 2) { unsigned long j = i + 1; unsigned long long k = i < 3 ? a[i] : 0; r[i] = b[i] | __builtin_subcll (k, b[i], c, &c); unsigned long long l = b[j]; if (j <= 3) { if (j == 3) k = a[3] & 0x7fffffffffffffffULL; else k = a[3]; } else k = 0; r[j] = l | __builtin_subcll (k, b[j], c, &c); } r[4] = (b[4] | __builtin_subcll (0, b[4] & 1, c, &c)) & 1; } might help understand better what bitintlower emits there, except it uses PARM_DECLs or automatic VAR_DECLs instead of the global ones (except for v) and n is 4 (I've used function argument only to avoid VRP figuring out earlier that certain paths are dead) and the var sizes is actually just 4 (for a) or 5 elts. That said, even _134 in the #c2 testcase at -O2 in the PHI argument is fishy, but the point is that bb 6 is really dead but it isn't known to the compiler yet; it is reached if _49 <= 2 is false, but given that _49 is incremented in increments of 2 and the array size is 5 maybe PRE knows that _49 then would have to be 4. bb 6 either jumps directly to bb 10 (if _140 (aka _49 + 1) > 3) or hops through bb 8 to bb 10.
next prev parent reply other threads:[~2024-02-07 20:24 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-02-05 18:13 [Bug tree-optimization/113774] New: " zsojka at seznam dot cz 2024-02-06 12:04 ` [Bug tree-optimization/113774] " zsojka at seznam dot cz 2024-02-07 18:28 ` jakub at gcc dot gnu.org 2024-02-07 20:24 ` jakub at gcc dot gnu.org [this message] 2024-02-08 13:54 ` jakub at gcc dot gnu.org 2024-02-08 14:04 ` rguenth at gcc dot gnu.org 2024-02-08 14:12 ` jakub at gcc dot gnu.org 2024-02-08 14:18 ` rguenth at gcc dot gnu.org 2024-02-09 10:06 ` cvs-commit at gcc dot gnu.org 2024-02-09 10:14 ` jakub at gcc dot gnu.org 2024-02-15 8:47 ` pinskia at gcc dot gnu.org
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