https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78085
Bug ID: 78085
Summary: Unexpected cltq instruction on Linux x86-64 for
conversion of positive int to long
Product: gcc
Version: 6.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: l.s.r at web dot de
Target Milestone: ---
Created attachment 39873
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39873&action=edit
Preprocesses test code
The attached file includes three functions that perform basic arithmetic
operations on an int and return the result as a long in different ways. The
first and the last are compiled to code that contains a cltq instruction, while
the second one omits it. I'd expect the other two to omit it as well because
the higher bits are already cleared by the arithmetic operations. Perhaps the
mov instruction in between prevents this elimination?
Using built-in specs.
COLLECT_GCC=gcc
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 6.2.0-6'
--with-bugurl=file:///usr/share/doc/gcc-6/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-6 --program-prefix=x86_64-linux-gnu- --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-6-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-6-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-6-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --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 6.2.0 20161010 (Debian 6.2.0-6)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-S' '-mtune=generic'
'-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/6/cc1 -E -quiet -v -imultiarch x86_64-linux-gnu
a.c -mtune=generic -march=x86-64 -O2 -fpch-preprocess -o a.i
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/6/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-linux-gnu/6/include
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/6/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-S' '-mtune=generic'
'-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/6/cc1 -fpreprocessed a.i -quiet -dumpbase a.c
-mtune=generic -march=x86-64 -auxbase a -O2 -version -o a.s
GNU C11 (Debian 6.2.0-6) version 6.2.0 20161010 (x86_64-linux-gnu)
compiled by GNU C version 6.2.0 20161010, GMP version 6.1.1, MPFR
version 3.1.5, MPC version 1.0.3, isl version 0.15
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C11 (Debian 6.2.0-6) version 6.2.0 20161010 (x86_64-linux-gnu)
compiled by GNU C version 6.2.0 20161010, GMP version 6.1.1, MPFR
version 3.1.5, MPC version 1.0.3, isl version 0.15
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 7b884337c1b75b774181841eebd770e3
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/6/:/usr/lib/gcc/x86_64-linux-gnu/6/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/6/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/6/:/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/6/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/6/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-S' '-mtune=generic'
'-march=x86-64'
