http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50038
Bug #: 50038
Summary: redundant zero extensions
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: tocarip.in...@gmail.com
Following code
void t_run_test(int Pels,unsigned char * ImageInPtr,unsigned char *
ImageOutPtr)
{
int i;
unsigned char xr, xg;
unsigned char xy=0;
for (i = 0; i < Pels; i++)
{
xr = *ImageInPtr++;
xg = *ImageInPtr++;
xy = (unsigned char) ((19595*xr + 38470*xg) >> 16);
*ImageOutPtr++ = xy;
}
}
Is compiled -O2 with both gcc 4.5.1
(Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,lto --enable-plugin
--enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-ppl --with-cloog --with-tune=generic --with-arch_32=i686
--build=x86_64-redhat-linux)
and trunk version
(Target: x86_64-unknown-linux-gnu
Configured with: ../configure --enable-languages=c --disable-bootsrap
Thread model: posix
gcc version 4.7.0 20110808 (experimental) (GCC) )
to
...
movzbl (%rsi), %edi
movzbl 1(%rsi), %eax
movq %rcx, %rsi
movzbl %dil, %edi <- redundant
movzbl %al, %eax <- redundant
imull $19595, %edi, %edi
imull $38470, %eax, %eax
addl %edi, %eax
...
For example icc does
...
movzbl (%rsi), %ecx
incl %eax
movzbl 1(%rsi), %r8d
addq $2, %rsi
imull $19595, %ecx, %r10d
....
Without unnecessary zero extensions.
