https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104054
--- Comment #8 from Uroš Bizjak <ubizjak at gmail dot com> ---
Without debug instructions, the compiler is able to rename insns to:
65: di:DI=si:DI
66: dx:DI=r11:DI
74: cx:QI=0x1
REG_EQUAL 0x1
41: L41:
42: NOTE_INSN_BASIC_BLOCK 6
43: NOTE_INSN_DELETED
but with debug instructions, the same sequence reads as:
50: debug b => si:TI
51: debug begin stmt marker
52: debug begin stmt marker
79: ax:DI=si:DI
80: dx:DI=di:DI
88: cx:QI=0x1
REG_EQUAL 0x1
53: L53:
54: NOTE_INSN_BASIC_BLOCK 6
55: debug b => si:TI
56: debug begin stmt marker
57: NOTE_INSN_DELETED
In the later case, the compiler is not able to rename ax:DI register in (insn
79) to di:DI, because debug insn 55 is still accessing di:DI in the register
si:TI - that is really formed from (si:DI,di:DI) register pair.
