https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83637
Bug ID: 83637
Summary: Inline assembly allocates the same register twice
Product: gcc
Version: 5.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: mini at cs dot technion.ac.il
Target Milestone: ---
Hi,
I am compiling this code:
int cmov(int pred, int t_val, int f_val) {
int result;
__asm__ volatile (
"mov %2, %0\n\t"
"test %1, %1\n\t"
"cmovz %3, %0\n\t"
"test %2, %2\n\t"
: [output] "=r" (result)
: [input] "r" (pred), "r" (t_val), "r" (f_val)
: "cc"
);
return result;
}
in the output, I see that the register allocated to the variable "result"
is the same one as for "pred".
This is the assembly it generates:
0x4005ac <cmov+22> mov %edx,%eax # result is eax
0x4005ae <cmov+24> test %eax,%eax # t_val is also eax!
0x4005b0 <cmov+26> cmove %ecx,%eax
0x4005b3 <cmov+29> test %edx,%edx
The output of this commans:
gcc -v -save-temps main.c
is:
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
5.4.0-6ubuntu1~16.04.4' --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 5.4.0-6ubuntu1~16.04.4)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/5/cc1 -E -quiet -v -imultiarch x86_64-linux-gnu
main.c -mtune=generic -march=x86-64 -fpch-preprocess -fstack-protector-strong
-Wformat -Wformat-security -o main.i
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/5/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-linux-gnu/5/include
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/5/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/5/cc1 -fpreprocessed main.i -quiet -dumpbase
main.c -mtune=generic -march=x86-64 -auxbase main -version
-fstack-protector-strong -Wformat -Wformat-security -o main.s
GNU C11 (Ubuntu 5.4.0-6ubuntu1~16.04.4) version 5.4.0 20160609
(x86_64-linux-gnu)
compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR
version 3.1.4, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C11 (Ubuntu 5.4.0-6ubuntu1~16.04.4) version 5.4.0 20160609
(x86_64-linux-gnu)
compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR
version 3.1.4, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 78b6f8b2ed219a71c67c16db887e4800
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=x86-64'
as -v --64 -o main.o main.s
GNU assembler version 2.29.1 (x86_64-pc-linux-gnu) using BFD version (GNU
Binutils) 2.29.1
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/5/collect2 -plugin
/usr/lib/gcc/x86_64-linux-gnu/5/liblto_plugin.so
-plugin-opt=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
-plugin-opt=-fresolution=main.res -plugin-opt=-pass-through=-lgcc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s --sysroot=/
--build-id --eh-frame-hdr -m elf_x86_64 --hash-style=gnu --as-needed
-dynamic-linker /lib64/ld-linux-x86-64.so.2 -z relro
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crt1.o
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/5/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/5
-L/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/5/../../../../lib -L/lib/x86_64-linux-gnu
-L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/x86_64-linux-gnu/5/../../.. main.o -lgcc --as-needed -lgcc_s
--no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc/x86_64-linux-gnu/5/crtend.o
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crtn.o
