[Bug tree-optimization/57701] New: Incorrect optimisation of inlined function with inline assembly when cross-compiling

[sqweek at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57701

            Bug ID: 57701
           Summary: Incorrect optimisation of inlined function with inline
                    assembly when cross-compiling
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sqweek at gmail dot com

Created attachment 30354
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30354&action=edit
Standalone source file for reproducing

gcc version 4.8.1 (GCC) 

My system is x86_64-unknown-linux-gnu, but I'm cross-compiling to x86 (-m32)

Configured with: /build/gcc-multilib/src/gcc-4.8.1/configure --prefix=/usr
--libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
--enable-threads=posix --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch
--enable-gnu-unique-object --enable-linker-build-id --enable-cloog-backend=isl
--disable-cloog-version-check --enable-lto --enable-gold --enable-ld=default
--enable-plugin --with-plugin-ld=ld.gold --with-linker-hash-style=gnu
--disable-install-libiberty --enable-multilib --disable-libssp --disable-werror
--enable-checking=release

I'm running the gcc-multilib binary from archlinux, which slightly modifies the
stock gcc build - it doesn't run fixinc.sh and adds -O2 to some configure
tests. I suspect they are not important, but in the interest of full disclosure
the  details available in the prepare() function at
https://projects.archlinux.org/svntogit/community.git/tree/repos/multilib-x86_64/PKGBUILD?h=packages/gcc-multilib


The problem: I've attached a program (which I've tried to make smaller but
failed to reproduce the problem) that runs fine when compiled with no flags,
but fails when compiled with -O. -O2 also fails, but -O3 works again *shrug*.

Build commands:
gcc -m32 fpe.c -o fpe       #produces a working binary
gcc -m32 -O fpe.c -o fpe-O  #produces the failing binary


Anyway, the code uses inline assembly to setup the floating point unit, then
calculates 0./0. The expected result is a NaN, but when compiled with -O the
FPU gets setup differently and we get a SIGFPE instead.

I'm pretty new at assembler, but I *think* I've ruled that out as the cause,
I've been stepping through the instructions in gdb and the results from the
inline assembly sections appear to be the same. The value returned from
getFPcontrol() seems to be where the differences begun.