The following code aligns and increments a pointer twice. I expect an offset of
8 with respect to the original address. Works as expected with an unoptimized
build, but an an offset of 4 is reported when compiled with -O2. The problem
seems to be the cast to (long&) before the arithmetic operations in the inline
align() function. Removing the (in case of char*) unnecessary first cast will
produce the correct output.
--- begin code ---
#include <stdio.h>
struct Test
{
char *p;
};
inline void align(char* &p)
{
((long &)p) += 3;
((long &)p) &= -4;
}
int main()
{
char buffer[8] = {0};
Test t = { buffer };
align(t.p);
t.p += 4;
align(t.p);
t.p += 4;
printf("%d\n", t.p - buffer);
}
--- end code ---
--- begin output ---
> g++ -v -Wall -O2 gcc-4-1-bug.cxx
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../gcc-4.1.0/configure --prefix=/space/gcc-4.1.0
--enable-languages=c,c++
Thread model: posix
gcc version 4.1.0
/space/gcc-4.1.0/libexec/gcc/i686-pc-linux-gnu/4.1.0/cc1plus -quiet -v
-D_GNU_SOURCE gcc-4-1-bug.cxx -quiet -dumpbase gcc-4-1-bug.cxx
-mtune=pentiumpro -auxbase gcc-4-1-bug -O2 -Wall -version -o /tmp/cc1idx2e.s
ignoring nonexistent directory
"/space/gcc-4.1.0/lib/gcc/i686-pc-linux-gnu/4.1.0/../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/space/gcc-4.1.0/lib/gcc/i686-pc-linux-gnu/4.1.0/../../../../include/c++/4.1.0
/space/gcc-4.1.0/lib/gcc/i686-pc-linux-gnu/4.1.0/../../../../include/c++/4.1.0/i686-pc-linux-gnu
/space/gcc-4.1.0/lib/gcc/i686-pc-linux-gnu/4.1.0/../../../../include/c++/4.1.0/backward
/usr/local/include
/space/gcc-4.1.0/include
/space/gcc-4.1.0/lib/gcc/i686-pc-linux-gnu/4.1.0/include
/usr/include
End of search list.
GNU C++ version 4.1.0 (i686-pc-linux-gnu)
compiled by GNU C version 4.1.0.
GGC heuristics: --param ggc-min-expand=98 --param ggc-min-heapsize=128169
Compiler executable checksum: 4ff5a0850335423f0b9670917725c57b
as -V -Qy -o /tmp/ccK9mBVm.o /tmp/cc1idx2e.s
GNU assembler version 2.16.91.0.2 (i586-suse-linux) using BFD version
2.16.91.0.2 20050720 (SuSE Linux)
/space/gcc-4.1.0/libexec/gcc/i686-pc-linux-gnu/4.1.0/collect2 --eh-frame-hdr
-m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o
/space/gcc-4.1.0/lib/gcc/i686-pc-linux-gnu/4.1.0/crtbegin.o -L.
-L/usr/local/lib -L/space/gcc-4.1.0/lib/gcc/i686-pc-linux-gnu/4.1.0
-L/space/gcc-4.1.0/lib/gcc/i686-pc-linux-gnu/4.1.0/../../.. /tmp/ccK9mBVm.o
-lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/space/gcc-4.1.0/lib/gcc/i686-pc-linux-gnu/4.1.0/crtend.o /usr/lib/crtn.o
> ./a.out
4
--- end output ---
--
Summary: inlining bug under optimization. (cast to reference)
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: d dot bonekaemper at rtsgroup dot net
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27114
