https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102914
Bug ID: 102914
Summary: spurious warnings are emitted on ARM about
non-delegitimized UNSPEC UNSPEC_TLS
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: ardb at kernel dot org
Target Milestone: ---
Target: ARM
The Linux/ARM kernel uses __builtin_thread_pointer() to access the TPIDRURO TLS
register, which triggers warning such as this one when using GCC 12.0.0. The
warning does not appear with 11.2
/home/ard/linux/init/calibrate.c: In function ‘calibrate_delay’:
/home/ard/linux/init/calibrate.c:275:6: note: non-delegitimized UNSPEC
UNSPEC_TLS (17) found in variable location
275 | void calibrate_delay(void)
| ^~~~~~~~~~~~~~~
This appears to be triggered by the presence of notes in the RTL such as the
one below:
(note 1826 74 76 2 (var_location this_cpu (mem:SI (plus:SI (unspec:SI [
(const_int 0 [0])
] UNSPEC_TLS)
(const_int 8 [0x8])) [5 MEM[(struct thread_info *)cur_24].cpu+0 S4
A64])) NOTE_INSN_VAR_LOCATION)
which are generated from dereferences of the (struct thread_info *) pointer
which is initialized from __builtin_thread_pointer().
(insn 50 2215 2217 2 (set (reg/v/f:SI 3 r3 [orig:124 cur ] [124])
(unspec:SI [
(const_int 0 [0])
] UNSPEC_TLS))
"/home/ard/linux/arch/arm/include/asm/current.h":36:8 401 {load_tp_hard}
(expr_list:REG_EQUIV (unspec:SI [
(const_int 0 [0])
] UNSPEC_TLS)
(nil)))
(insn 54 2226 1499 2 (set (reg/v:SI 2 r2 [orig:125 this_cpu ] [125])
(mem:SI (plus:SI (reg/v/f:SI 3 r3 [orig:124 cur ] [124])
(const_int 8 [0x8])) [5 MEM[(struct thread_info *)cur_24].cpu+0
S4 A64])) "/home/ard/linux/init/calibrate.c":279:6 990 {*thumb2_movsi_insn}
(expr_list:REG_DEAD (reg/v/f:SI 3 r3 [orig:124 cur ] [124])
(nil)))
