https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104814
Bug ID: 104814 Summary: [10/11/12 Regression] ifcvt: Deleting live variable in IF-CASE-2 Product: gcc Version: 12.0 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: rtl-optimization Assignee: unassigned at gcc dot gnu.org Reporter: stefansf at linux dot ibm.com Target Milestone: --- Target: s390x-*-* Created attachment 52570 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52570&action=edit dump ce2 short a = 0; static long b = 0; int c = 7; char d = 0; short *e = &a; long f = 0; unsigned long g (unsigned long h, long j) { return j == 0 ? h : h / j; } int main (void) { long k = f; for (; c; --c) { for (int i = 0; i < 7; ++i) ; long m = g (f, --b); d = ((char)m | *e) <= 43165; } if (b != -7) __builtin_abort (); return 0; } Variable b should be decremented in each iteration of the outer loop and thus equal -7 at the end. After combine a load, decrement, and store insn exists: (insn 13 12 14 3 (set (reg:DI 62 [ b_lsm.16 ]) (mem/c:DI (const:DI (plus:DI (symbol_ref:DI ("*.LANCHOR0") [flags 0x182]) (const_int 8 [0x8]))) [1 b+0 S8 A64])) 1469 {*movdi_64} (nil)) (jump_insn 40 39 46 6 (parallel [ (set (pc) (if_then_else (ne (reg:DI 62 [ b_lsm.16 ]) (const_int 1 [0x1])) (label_ref 38) (pc))) (set (reg:DI 62 [ b_lsm.16 ]) (plus:DI (reg:DI 62 [ b_lsm.16 ]) (const_int -1 [0xffffffffffffffff]))) (clobber (scratch:DI)) (clobber (reg:CC 33 %cc)) ]) "t.c":8:63 2164 {doloop_di} (expr_list:REG_UNUSED (reg:CC 33 %cc) (int_list:REG_BR_PROB 536870916 (nil))) -> 38) (insn 48 47 49 7 (set (mem/c:DI (const:DI (plus:DI (symbol_ref:DI ("*.LANCHOR0") [flags 0x182]) (const_int 8 [0x8]))) [1 b+0 S8 A64]) (reg:DI 62 [ b_lsm.16 ])) 1469 {*movdi_64} (expr_list:REG_DEAD (reg:DI 62 [ b_lsm.16 ]) (nil))) Pass ce2 deletes jump insn 40 including the decrement of variable b: IF-CASE-2 found, start 6, else 4 deleting insn with uid = 40. deleting block 4 Conversion succeeded on pass 1. Thus variable b equals 0 in the end.