http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40893
--- Comment #4 from paul walmsley <paul at pwsan dot com> 2010-10-08 17:17:24
UTC ---
The bug also appears without volatile:
----
/* generates an unnecessary uxth */
void foo(unsigned short a, unsigned short b, unsigned short c,
unsigned short *e, unsigned short *f)
{
*e = (a + b) + c;
*f = (a + b) - c;
}
/* works as expected */
void bar(unsigned short a, unsigned short b, unsigned short c,
unsigned short *e)
{
*e = (a + b) + c;
}
/* works as expected */
void baz(unsigned short a, unsigned short b, unsigned short c,
unsigned short *e)
{
*e = (a + b) - c;
}
-----
compiled and dumped with:
arm-linux-gnueabi-gcc -O2 -c test.c ; objdump -DS test.o
produces:
-----
Disassembly of section .text:
00000000 <foo>:
0: e0811000 add r1, r1, r0
4: e1a01801 lsl r1, r1, #16
8: e1a01821 lsr r1, r1, #16
c: e0620001 rsb r0, r2, r1
10: e0821001 add r1, r2, r1
14: e1c310b0 strh r1, [r3]
18: e59d3000 ldr r3, [sp]
1c: e1c300b0 strh r0, [r3]
20: e12fff1e bx lr
00000024 <bar>:
24: e0811000 add r1, r1, r0
28: e0822001 add r2, r2, r1
2c: e1c320b0 strh r2, [r3]
30: e12fff1e bx lr
00000034 <baz>:
34: e0811000 add r1, r1, r0
38: e0622001 rsb r2, r2, r1
3c: e1c320b0 strh r2, [r3]
40: e12fff1e bx lr
-----
gcc -v:
Using built-in specs.
Target: arm-linux-gnueabi
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.5-2'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.4 --enable-shared --enable-multiarch
--enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/arm-linux-gnueabi/include/c++/4.4.5
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-objc-gc --disable-sjlj-exceptions --enable-checking=release
--program-prefix=arm-linux-gnueabi- --includedir=/usr/arm-linux-gnueabi/include
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=arm-linux-gnueabi
--with-headers=/usr/arm-linux-gnueabi/include
--with-libs=/usr/arm-linux-gnueabi/lib
Thread model: posix
gcc version 4.4.5 (Debian 4.4.5-2)
