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[Bug c/77478] New: Incorrect code generated with -O3, m32, -msse2 and -ffast-math


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77478

            Bug ID: 77478
           Summary: Incorrect code generated with -O3, m32, -msse2 and
                    -ffast-math
           Product: gcc
           Version: 5.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc_bugzilla at appletonaudio dot com
  Target Milestone: ---

Created attachment 39555
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39555&action=edit
The output of -save-temps

Apologies if I've selected the wrong component - I suspect this issue is
something wrong in one of the optimization phases, but was not sure what
"component" to select.

The attached program will crash with a segmentation fault when compiled with
the specified arguments. The generated code appears to be generating aligned
vector load instructions on a not properly aligned address. I've tried to
reduce the program and compiler arguments as much as I can into something which
still triggers the behavior.

* the exact version of GCC;
* the system type;
* the options given when GCC was configured/built;

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
5.4.0-6ubuntu1~16.04.2' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.2) 

(This GCC was obtained using apt)

* the complete command line that triggers the bug;

gcc -msse2 -O3 -ffast-math -m32 test.c

* the compiler output (error messages, warnings, etc.); and

The compiler produces no warnings with -Wextra. When I tried to use the
undefined behavior sanitizer (-fsanitize=undefined), the crash vanishes.

* the preprocessed file (*.i*) that triggers the bug, generated by adding
-save-temps to the complete compilation command, or, in the case of a bug
report for the GNAT front end, a complete set of source files (see below).

This file is attached and is identical to the .c file which generated it (minus
the hash-prefixed lines at the top).

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