[Bug rtl-optimization/69047] New: memcpy of 64-bit integer to 32-bit integer causes pointless stack operations on ARM

[x.fix at o2 dot pl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69047

            Bug ID: 69047
           Summary: memcpy of 64-bit integer to 32-bit integer causes
                    pointless stack operations on ARM
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: x.fix at o2 dot pl
  Target Milestone: ---

Created attachment 37131
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37131&action=edit
d.c

When a function does memcpy to a local integer and returns it, pointless stack
operations are done (subtraction, and addition just after that).

Command line
============

arm-none-eabi-gcc -O3 -S -o- d.c

Output
======

Assembly code containing following function.

f:
        @ Function supports interworking.
        @ args = 0, pretend = 0, frame = 8
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        sub     sp, sp, #8
        add     sp, sp, #8
        @ sp needed
        bx      lr
        .size   f, .-f

Version information
===================

Using built-in specs.
COLLECT_GCC=arm-none-eabi-gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/arm-none-eabi/5.3.0/lto-wrapper
Target: arm-none-eabi
Configured with: /build/arm-none-eabi-gcc/src/gcc-5.3.0/configure
--target=arm-none-eabi --prefix=/usr --with-sysroot=/usr/arm-none-eabi
--with-native-system-header-dir=/include --libexecdir=/usr/lib
--enable-languages=c,c++ --enable-plugins --disable-decimal-float
--disable-libffi --disable-libgomp --disable-libmudflap --disable-libquadmath
--disable-libssp --disable-libstdcxx-pch --disable-nls --disable-shared
--disable-threads --disable-tls --with-gnu-as --with-gnu-ld --with-system-zlib
--with-newlib --with-headers=/usr/arm-none-eabi/include
--with-python-dir=share/gcc-arm-none-eabi --with-gmp --with-mpfr --with-mpc
--with-isl --with-libelf --enable-gnu-indirect-function
--with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm'
--with-pkgversion='Arch Repository' --with-bugurl=https://bugs.archlinux.org/
--with-multilib-list=armv6-m,armv7-m,armv7e-m,armv7-r
Thread model: single
gcc version 5.3.0 (Arch Repository)