https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93674
Bug ID: 93674
Summary: GCC eliminates conditions it should not, when
strict-enums is on
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gbuella at gmail dot com
Target Milestone: ---
$ cat code.cc
enum some_enum { x = 1000 };
void sink(some_enum);
void func()
{
for (int i = 0; i < 3; ++i) {
for (int j = 3; j >= 0; --j) {
sink((some_enum)(i + j));
}
}
}
$ g++-8 -Wall -Wextra -pedantic -std=c++14 code.cc -fstrict-enums -S -o
/dev/stdout -fno-dwarf2-cfi-asm -O3 | head -20
.file "code.cc"
.text
.p2align 4,,15
.globl _Z4funcv
.type _Z4funcv, @function
_Z4funcv:
.LFB0:
pushq %rbx
.LCFI0:
movl $3, %ebx
.p2align 4,,10
.p2align 3
.L2:
movl %ebx, %edi
subl $1, %ebx
call _Z4sink9some_enum@PLT
jmp .L2
.LFE0:
.size _Z4funcv, .-_Z4funcv
.section .eh_frame,"a",@progbits
$ g++-8 --version
g++-8 (Ubuntu 8.3.0-6ubuntu1~18.04.1) 8.3.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Notice the infinite loop in generated assembly (unconditional jmp to .L2).
This doesn't happen without "-fstruct-enums", doesn't happen without -O2 or
-O3.
I'v seen this bug with GCC 8, GCC 9 .
GCC-7 seems to be OK.
I spent hours trying to find more compact code for reproducing it, but I just
couldn't...
The loop, and the addition (i + j) seems to be needed to trigger this.
