https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68841
--- Comment #4 from ktkachov at gcc dot gnu.org ---
I suspect that more aggressive if-conversion is exposing a bug in another RTL
pass. If-conversion creates:
(insn 22 21 73 7 (set (reg:CCGC 17 flags)
(compare:CCGC (reg/v:SI 88 [ i ])
(const_int 3 [0x3]))) file.c:19 7 {*cmpsi_1}
(nil))
(insn 73 22 74 7 (parallel [
(set (reg:SI 94)
(ashift:SI (reg/v:SI 88 [ i ])
(const_int 1 [0x1])))
(clobber (reg:CC 17 flags))
]) zdenek.c:20 525 {*ashlsi3_1}
(nil))
(insn 74 73 75 7 (set (reg/v:SI 93 [ k ])
(eq:SI (reg:CCGC 17 flags)
(const_int 0 [0]))) file.c:20 626 {*setcc_si_1_movzbl}
(nil))
(insn 75 74 76 7 (set (reg:SI 95)
(plus:SI (ashift:SI (reg/v:SI 93 [ k ])
(const_int 2 [0x2]))
(const_int 8 [0x8]))) file.c:20 212 {*leasi}
(nil))
(insn 76 75 77 7 (set (reg:CCGC 17 flags)
(compare:CCGC (reg/v:SI 88 [ i ])
(const_int 4 [0x4]))) file.c:20 7 {*cmpsi_1}
(nil))
(insn 77 76 33 7 (set (reg/v:SI 87 [ k ])
(if_then_else:SI (lt (reg:CCGC 17 flags)
(const_int 0 [0]))
(reg:SI 95)
(reg:SI 94))) file.c:20 966 {*movsicc_noc}
(nil))
but during lr_shrinkage the first compare in insn 22 is deemed dead code and
eliminated:
(insn 73 21 74 7 (parallel [
(set (reg:SI 94)
(ashift:SI (reg/v:SI 88 [ i ])
(const_int 1 [0x1])))
(clobber (reg:CC 17 flags))
]) file.c:20 525 {*ashlsi3_1}
(nil))
(insn 74 73 75 7 (set (reg/v:SI 93 [ k ])
(eq:SI (reg:CCGC 17 flags)
(const_int 0 [0]))) file.c:20 626 {*setcc_si_1_movzbl}
(expr_list:REG_DEAD (reg:CCGC 17 flags)
(nil)))
(insn 75 74 76 7 (set (reg:SI 95)
(plus:SI (ashift:SI (reg/v:SI 93 [ k ])
(const_int 2 [0x2]))
(const_int 8 [0x8]))) file.c:20 212 {*leasi}
(expr_list:REG_DEAD (reg/v:SI 93 [ k ])
(nil)))
(insn 76 75 77 7 (set (reg:CCGC 17 flags)
(compare:CCGC (reg/v:SI 88 [ i ])
(const_int 4 [0x4]))) zdenek.c:20 7 {*cmpsi_1}
(nil))
(insn 77 76 33 7 (set (reg/v:SI 87 [ k ])
(if_then_else:SI (lt (reg:CCGC 17 flags)
(const_int 0 [0]))
(reg:SI 95)
(reg:SI 94))) file.c:20 966 {*movsicc_noc}
(expr_list:REG_DEAD (reg:SI 95)
(expr_list:REG_DEAD (reg:SI 94)
(expr_list:REG_DEAD (reg:CCGC 17 flags)
(nil)))))
However, the result of the comparison had a use in insn 74.
I'll dig deeper, but I'm not very familiar with that part of the code, so any
insight would be appreciated.
