In one case the C compiler can optimize away an inline memcpy() on a
MIPS target. The problem was duplicated with GCC 3.2.1 and 3.3.3.
The problem does not affect x86 targets or GCC 4.x (tested on 4.2.4).
The MIPS cross-compiler runs under RHEL. Tested MIPS cross-compilers
under Cygwin and Mingw with the same results.
This is the test code and the resulting output. The "if" statement and
16-byte memcpy() are optimized away, leaving only the 4-byte memcpy.
Compile with: mipsisa32-elf-gcc -O2 -c test.c
---------------------------
#include <string.h>
typedef struct {
char C[16];
int E;
} st;
void f( st *S, char* c );
void f( st *S, char* c )
{
if ( S->E == 6 )
memcpy( &S->C, c, 16 );
else
memcpy( &S->C, c, 4 );
}
---------------------------
00000000 <f>:
0: 88a20000 lwl v0,0(a1)
4: 98a20003 lwr v0,3(a1)
8: a8820000 swl v0,0(a0)
c: 03e00008 jr ra
10: b8820003 swr v0,3(a0)
---------------------------
Compiler info:
$ mipsisa32-elf-gcc -v
Reading specs from
/tools/ecos/3.2.1_opt/Linux/opt/ecos/gnutools/mipsisa32-elf/bin/../lib/gcc-lib/mipsisa32-elf/3.2.1/specs
Configured with: /home/msieweke/ecos20/gnutools-src/gcc-3.2.1/configure
--target=mipsisa32-elf --prefix=/home/msieweke/gnutools_321
--enable-languages=c,c++ --enable-gofast --with-gnu-as --with-gnu-ld
--with-newlib
--with-gxx-include-dir=/home/msieweke/gnutools_321/mipsisa32-elf/include -v
Thread model: single
gcc version 3.2.1
--
Summary: inline memcpy() incorrectly optimized on MIPS target
Product: gcc
Version: 3.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: msieweke at broadcom dot com
GCC build triplet: i386-gnu-linux
GCC host triplet: i386-gnu-linux
GCC target triplet: mipsisa32-elf
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39755
