https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101188
Georg-Johann Lay <gjl at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Last reconfirmed|2021-06-25 00:00:00 |2023-5-24 Component|target |rtl-optimization CC| |vmakarov at gcc dot gnu.org Keywords| |ra --- Comment #3 from Georg-Johann Lay <gjl at gcc dot gnu.org> --- With the test case from comment #2 $ avr-gcc fail1.c -save-temps -dp -dumpbase "" -mmcu=atmega128 -c -Os -da typedef __UINT8_TYPE__ uint8_t; typedef __UINT16_TYPE__ uint16_t; typedef __UINT32_TYPE__ uint32_t; typedef uint8_t (*fn1)(void *a); typedef void (*fn2)(void *a, const uint32_t *arg); struct S { uint8_t buffer[64]; uint16_t n; fn2 f2; void *a; fn1 f1; }; volatile uint16_t x; void foo (uint16_t); void __attribute__((noinline)) testfn (struct S *self) { uint32_t arg; foo (self->n); self->n++; self->f2 (self->a, &arg); self->buffer[0] = self->f1 (self->a); } For all what I can tell, this looks like a bug in the register allocator, not a backend issue. Allow me to CC Vladimir. With current master 14.0.0 20230523 the .postreload dump shows that insn 14 uses HI:30, and insn 17 continues using HI:30. But for insn 15, reload provides scratch QI:31 which shreds the value in HI:30: (insn 14 13 44 2 (set (mem:HI (reg:HI 30 r30) [1 self_10(D)->n+0 S2 A8]) (reg:HI 24 r24 [56])) "fail1.c":28:12 101 {*movhi_split} (nil)) (insn 44 14 15 2 (set (reg/f:HI 14 r14 [58]) (reg/v/f:HI 16 r16 [orig:51 self ] [51])) "fail1.c":29:5 101 {*movhi_split} (nil)) (insn 15 44 16 2 (parallel [ (set (reg/f:HI 14 r14 [58]) (plus:HI (reg/f:HI 14 r14 [58]) (const_int 68 [0x44]))) (clobber (reg:QI 31 r31)) ]) "fail1.c":29:5 175 {addhi3_clobber} (nil)) (note 16 15 17 2 NOTE_INSN_DELETED) >>> Where is insn 45 ??? (insn 17 16 18 2 (set (reg/f:HI 30 r30 [60]) (plus:HI (reg/f:HI 30 r30 [60]) (const_int 2 [0x2]))) "fail1.c":29:9 165 {*addhi3_split} (nil)) In the .reload dump however, there is a move insn 45 that restores HI:30 after the addhi3_clobber: ... (note 16 15 45 2 NOTE_INSN_DELETED) (insn 45 16 17 2 (set (reg/f:HI 30 r30 [60]) (reg/v/f:HI 16 r16 [orig:51 self ] [51])) "fail1.c":28:9 101 {*movhi_split} (nil)) (insn 17 45 18 2 (parallel [ (set (reg/f:HI 30 r30 [60]) (plus:HI (reg/f:HI 30 r30 [60]) (const_int 66 [0x42]))) (clobber (scratch:QI)) ]) "fail1.c":28:9 175 {addhi3_clobber} (nil))