The inline assembly can end up generating instructions of the form
mulq %rax when the two operands should be distinct (i.e. one should not compute
%rax * %rax, a square but a product of two different numbers).(The x86 mulq
instruction will compute the product of the operand with the %rax register).
This happens with -O1 and any higher level of optimizations.
Version information:
gcc -m64 -c -O1 -v -save-temps gnu_bug_test.c
Using built-in specs.
Target: x86_64-suse-linux
Configured with: ../configure --enable-threads=posix --prefix=/usr
--with-local-prefix=/usr/local --infodir=/usr/share/info
--mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64
--enable-languages=c,c++,objc,fortran,obj-c++,java,ada
--enable-checking=release --with-gxx-include-dir=/usr/include/c++/4.2.1
--enable-ssp --disable-libssp --disable-libgcj --with-slibdir=/lib64
--with-system-zlib --enable-shared --enable-__cxa_atexit
--enable-libstdcxx-allocator=new --disable-libstdcxx-pch --program-suffix=-4.2
--enable-version-specific-runtime-libs --without-system-libunwind
--with-cpu=generic --host=x86_64-suse-linux
Thread model: posix
gcc version 4.2.1 (SUSE Linux)
/usr/lib64/gcc/x86_64-suse-linux/4.2.1/cc1 -E -quiet -v gnu_bug_test.c -m64
-mtune=generic -O1 -fpch-preprocess -o gnu_bug_test.i
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/usr/lib64/gcc/x86_64-suse-linux/4.2.1/include
/usr/lib64/gcc/x86_64-suse-linux/4.2.1/../../../../x86_64-suse-linux/include
/usr/include
End of search list.
/usr/lib64/gcc/x86_64-suse-linux/4.2.1/cc1 -fpreprocessed gnu_bug_test.i
-quiet -dumpbase gnu_bug_test.c -m64 -mtune=generic -auxbase gnu_bug_test -O1
-version -o gnu_bug_test.s
GNU C version 4.2.1 (SUSE Linux) (x86_64-suse-linux)
compiled by GNU C version 4.2.1 (SUSE Linux).
GGC heuristics: --param ggc-min-expand=94 --param ggc-min-heapsize=120388
Compiler executable checksum: 15875aa798ad559dcc04a8709924cdb9
/usr/lib64/gcc/x86_64-suse-linux/4.2.1/../../../../x86_64-suse-linux/bin/as -V
-Qy --64 -o gnu_bug_test.o gnu_bug_test.s
GNU assembler version 2.17.50 (x86_64-suse-linux) using BFD version (GNU
Binutils) 2.17.50.20070726-14 (SUSE Linux)
--
Summary: wrong register used when generating assembly with -O1
Product: gcc
Version: 4.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: inline-asm
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: fabrice at mocana dot com
GCC build triplet: x86_64-suse-linux
GCC host triplet: x86_64-suse-linux
GCC target triplet: x86_64-suse-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39116
