In the attached standalone test case (depends only on ::memcpy in string.h), the test fails when compiled with -O1 but succeeds with all other optimisations (-O0, -O2, -O3).
Files attached: testOpt.cpp - standalone test with compilation information included in the file. testOpt.ii Below is the stdout/stderr for the compilation: [mich...@belly gcc_issues]$ g++ -v -save-temps -O1 testOpt.cpp -o testOpt Using built-in specs. Target: i586-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-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --enable-plugin --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=i586 --build=i586-redhat-linux Thread model: posix gcc version 4.4.1 20090725 (Red Hat 4.4.1-2) (GCC) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-o' 'testOpt' '-shared-libgcc' '-mtune=generic' '-march=i586' /usr/libexec/gcc/i586-redhat-linux/4.4.1/cc1plus -E -quiet -v -D_GNU_SOURCE testOpt.cpp -mtune=generic -march=i586 -O1 -fpch-preprocess -o testOpt.ii ignoring nonexistent directory "/usr/lib/gcc/i586-redhat-linux/4.4.1/include-fixed" ignoring nonexistent directory "/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../i586-redhat-linux/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1 /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/i586-redhat-linux /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/backward /usr/local/include /usr/lib/gcc/i586-redhat-linux/4.4.1/include /usr/include End of search list. COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-o' 'testOpt' '-shared-libgcc' '-mtune=generic' '-march=i586' /usr/libexec/gcc/i586-redhat-linux/4.4.1/cc1plus -fpreprocessed testOpt.ii -quiet -dumpbase testOpt.cpp -mtune=generic -march=i586 -auxbase testOpt -O1 -version -o testOpt.s GNU C++ (GCC) version 4.4.1 20090725 (Red Hat 4.4.1-2) (i586-redhat-linux) compiled by GNU C version 4.4.1 20090725 (Red Hat 4.4.1-2), GMP version 4.2.4, MPFR version 2.4.1. GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: e983968af33489f00d517096be08dea1 COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-o' 'testOpt' '-shared-libgcc' '-mtune=generic' '-march=i586' as -V -Qy -o testOpt.o testOpt.s GNU assembler version 2.19.51.0.14 (i586-redhat-linux) using BFD version version 2.19.51.0.14-1.fc11 20090722 COMPILER_PATH=/usr/libexec/gcc/i586-redhat-linux/4.4.1/:/usr/libexec/gcc/i586-redhat-linux/4.4.1/:/usr/libexec/gcc/i586-redhat-linux/:/usr/lib/gcc/i586-redhat-linux/4.4.1/:/usr/lib/gcc/i586-redhat-linux/:/usr/libexec/gcc/i586-redhat-linux/4.4.1/:/usr/libexec/gcc/i586-redhat-linux/:/usr/lib/gcc/i586-redhat-linux/4.4.1/:/usr/lib/gcc/i586-redhat-linux/ LIBRARY_PATH=/usr/lib/gcc/i586-redhat-linux/4.4.1/:/usr/lib/gcc/i586-redhat-linux/4.4.1/:/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-o' 'testOpt' '-shared-libgcc' '-mtune=generic' '-march=i586' /usr/libexec/gcc/i586-redhat-linux/4.4.1/collect2 --eh-frame-hdr --build-id -m elf_i386 --hash-style=gnu -dynamic-linker /lib/ld-linux.so.2 -o testOpt /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../crt1.o /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../crti.o /usr/lib/gcc/i586-redhat-linux/4.4.1/crtbegin.o -L/usr/lib/gcc/i586-redhat-linux/4.4.1 -L/usr/lib/gcc/i586-redhat-linux/4.4.1 -L/usr/lib/gcc/i586-redhat-linux/4.4.1/../../.. testOpt.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/i586-redhat-linux/4.4.1/crtend.o /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../crtn.o -- Summary: -O1 optimisation of for loops in some cases omits essential functionality resulting in failed applications Product: gcc Version: 4.4.1 Status: UNCONFIRMED Severity: blocker Priority: P3 Component: c++ AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: mhenson at clarityvi dot com GCC target triplet: i586-redhat-linux http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41287
