https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89056
Bug ID: 89056
Summary: Optimizer generates bad code for non-void function
that fails to return a value
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: darryl_okahata at keysight dot com
Target Milestone: ---
Created attachment 45530
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45530&action=edit
preprocessed file
System: ancient Red Hat Enterprise Linux Server release 6.10 (Santiago)
Intel x86_64 system.
g++ -v
Using built-in specs.
COLLECT_GCC=/hped/builds/tfstools/gcc540/linux_x86_64//gcc/8.2.0/bin/g++_x86_64
COLLECT_LTO_WRAPPER=/a/new/sr/proton/d11/build/tfstools/gcc472/linux_x86_64/gcc/8.2.0/bin/../libexec/gcc/x86_64-pc-linux-gnu/8.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --enable-checking=release --enable-languages=c,c++
--enable-shared --enable-threads=posix --enable-__cxa_atexit
--enable-clocale=gnu --disable-multilib --with-system-zlib
--prefix=/hped/builds/tfstools/gcc472/linux_x86_64/gcc/8.2.0_rebld
--with-gmp=/gfs/sr/sherry/d1/local/dbjornba/btmp
--with-mpfr=/gfs/sr/sherry/d1/local/dbjornba/btmp
--with-mpc=/gfs/sr/sherry/d1/local/dbjornba/btmp
Thread model: posix
gcc version 8.2.0 (GCC)
If you have cruddy code with a non-void function that fails to return a value,
the gcc optimizer can generate an "infinite" loop for a simple iterative loop
(see the end of the *.ii file):
bool test::bah(void)
{
std::deque<struct foo>::iterator iter;
for (iter = values.begin(); iter != values.end(); iter++)
iter->myval -= 0.1;
// returning a value here causes correct code to be generated.
}
The bug can be easily seen using:
g++ -S -O badbad.cc
badbad.cc: In member function 'bool test::bah()':
badbad.cc:42:1: warning: no return statement in function returning non-void
[-Wreturn-type]
}
^
The generated assembly code shows an "infinite" loop for the simple iterative
loop (which only "terminates" when a bus error occurs). The correct code is
generated if you add a proper return value.
Yes, this is a poster child for using -Werror=return-type, but gcc should still
not generate bad code (the return value will, of course, still be undefined).
