http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58416 Bug ID: 58416 Summary: Incorrect x87-based union copying code Product: gcc Version: 4.6.3 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: stichnot at google dot com Created attachment 30819 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30819&action=edit .ii file generated from nantest1.cpp The program below produces incorrect code on x86-32 with gcc 4.6.3. (It was also found to fail in 4.7 but succeed in 4.8.) The problem happens when: 1. The union is initialized via its 64-bit double field 2. The union is then updated via its 64-bit integer field 3. The union is copied to another variable When this happens, the 64-bit copy in step 3 is done via the x87 fldl/fstpl instructions. If the 64-bit integer value in step 2 happens to be an sNaN pattern, the fldl instruction transforms it to a qNaN pattern and the fstpl instruction writes the wrong value. If step 1 is omitted, the x87 instructions are not used and the code is correct. This suggests that the optimization of using x87 for 64-bit transfers is enabled when a use of the double field is found, whereas it should probably only happen if a *live* use of the double field is found. // Compile with g++ -O3 -m32 // -O[123] all exhibit the problem. #include #include #include union MyClass { MyClass() : DoubleVal(0.0) {} // this ctor causes failure //MyClass() : IntVal(0) {} // this ctor works correctly int64_t IntVal; double DoubleVal; }; __attribute__((noinline)) void create(MyClass &dest, int64_t Val) { MyClass MCOp; MCOp.IntVal = Val; dest = MCOp; } int main(int argc, char **argv) { MyClass copy; int64_t magic = 0xfff0000000000001; // happens to be sNaN create(copy, magic); // copy is changed to qNaN printf("magic=%llx\ncopy= %llx\n", magic, copy.IntVal); assert(magic == copy.IntVal); return 0; } $ g++ -v -save-temps -Wall -Wextra -fno-strict-aliasing -fwrapv -O3 -m32 nantest1.cpp Using built-in specs. COLLECT_GCC=/usr/bin/g++ COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.6.3-1ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-fno-strict-aliasing' '-fwrapv' '-O3' '-m32' '-shared-libgcc' '-mtune=generic' '-march=i686' /usr/lib/gcc/x86_64-linux-gnu/4.6/cc1plus -E -quiet -v -imultilib 32 -imultiarch i386-linux-gnu -D_GNU_SOURCE nantest1.cpp -m32 -mtune=generic -march=i686 -Wall -Wextra -fno-strict-aliasing -fwrapv -O3 -fpch-preprocess -fstack-protector -o nantest1.ii ignoring nonexistent directory "/usr/local/include/i386-linux-gnu" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../x86_64-linux-gnu/include" ignoring nonexistent directory "/usr/include/i386-linux-gnu" #include "..." search starts here: #include <...> search starts here: /usr/include/c++/4.6 /usr/include/c++/4.6/x86_64-linux-gnu/32 /usr/include/c++/4.6/backward /usr/lib/gcc/x86_64-linux-gnu/4.6/include /usr/local/include /usr/lib/gcc/x86_64-linux-gnu/4.6/include-fixed /usr/include End of search list. COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-fno-strict-aliasing' '-fwrapv' '-O3' '-m32' '-shared-libgcc' '-mtune=generic' '-march=i686' /usr/lib/gcc/x86_64-linux-gnu/4.6/cc1plus -fpreprocessed nantest1.ii -quiet -dumpbase nantest1.cpp -m32 -mtune=generic -march=i686 -auxbase nantest1 -O3 -Wall -Wextra -version -fno-strict-aliasing -fwrapv -fstack-protector -o nantest1.s GNU C++ (Ubuntu/Linaro 4.6.3-1ubuntu5) version 4.6.3 (x86_64-linux-gnu) compiled by GNU C version 4.6.3, GMP version 5.0.2, MPFR version 3.1.0-p3, MPC version 0.9 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU C++ (Ubuntu/Linaro 4.6.3-1ubuntu5) version 4.6.3 (x86_64-linux-gnu) compiled by GNU C version 4.6.3, GMP version 5.0.2, MPFR version 3.1.0-p3, MPC version 0.9 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 65b5171ac1bd7b3f07dbea6bdb24be3d nantest1.cpp:21:5: warning: unused parameter ‘argc’ [-Wunused-parameter] nantest1.cpp:21:5: warning: unused parameter ‘argv’ [-Wunused-parameter] COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-fno-strict-aliasing' '-fwrapv' '-O3' '-m32' '-shared-libgcc' '-mtune=generic' '-march=i686' as --32 -o nantest1.o nantest1.s COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.6/:/usr/lib/gcc/x86_64-linux-gnu/4.6/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.6/:/usr/lib/gcc/x86_64-linux-gnu/ LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.6/32/:/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../i386-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib32/:/lib/i386-linux-gnu/:/lib/../lib32/:/usr/lib/i386-linux-gnu/:/usr/lib/../lib32/:/usr/lib/gcc/x86_64-linux-gnu/4.6/:/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../i386-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../:/lib/i386-linux-gnu/:/lib/:/usr/lib/i386-linux-gnu/:/usr/lib/ COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-fno-strict-aliasing' '-fwrapv' '-O3' '-m32' '-shared-libgcc' '-mtune=generic' '-march=i686' /usr/lib/gcc/x86_64-linux-gnu/4.6/collect2 --sysroot=/ --build-id --no-add-needed --as-needed --eh-frame-hdr -m elf_i386 --hash-style=gnu -dynamic-linker /lib/ld-linux.so.2 -z relro /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib32/crt1.o /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib32/crti.o /usr/lib/gcc/x86_64-linux-gnu/4.6/32/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/4.6/32 -L/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../i386-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib32 -L/lib/i386-linux-gnu -L/lib/../lib32 -L/usr/lib/i386-linux-gnu -L/usr/lib/../lib32 -L/usr/lib/gcc/x86_64-linux-gnu/4.6 -L/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../i386-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/4.6/../../.. -L/lib/i386-linux-gnu -L/usr/lib/i386-linux-gnu nantest1.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/4.6/32/crtend.o /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib32/crtn.o >From gcc-bugs-return-429782-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Sep 13 20:17:37 2013 Return-Path: Delivered-To: listarch-gcc-bugs@gcc.gnu.org Received: (qmail 1636 invoked by alias); 13 Sep 2013 20:17:37 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Delivered-To: mailing list gcc-bugs@gcc.gnu.org Received: (qmail 1599 invoked by uid 48); 13 Sep 2013 20:17:33 -0000 From: "jorge.aparicio.r at gmail dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/57657] [regression from 4.7] Reports incorrect cache sizes on corei7 Date: Fri, 13 Sep 2013 20:17:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c X-Bugzilla-Version: 4.8.1 X-Bugzilla-Keywords: X-Bugzilla-Severity: minor X-Bugzilla-Who: jorge.aparicio.r at gmail dot com X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: cc Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-SW-Source: 2013-09/txt/msg01022.txt.bz2 Content-length: 5111 http://gcc.gnu.org/bugzilla/show_bug.cgi?idW657 Jorge Aparicio changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jorge.aparicio.r at gmail dot com --- Comment #1 from Jorge Aparicio --- I can confirm this gcc-4.8.1 regression on three different Intel CPUs (core i3 2nd gen, core i5 1rst gen and core i7 4th gen), but the regression actually comes from gcc-4.8.0 CONCLUSION: gcc-4.8.0 reports the correct cache sizes when -march=native is used gcc-4.8.1 always reports 1) l1 cache size = 0, 2) l1 line cache size = 0 and 3) l2 cache size = 256; when -march=native is used OBSERVATIONS: #### Processor 1 #### $ lscpu | grep 'name\|cache' Model name: Intel(R) Core(TM) i7-4702MQ CPU @ 2.20GHz L1d cache: 32K L1i cache: 32K L2 cache: 256K L3 cache: 6144K $ gcc 4.8.0 -march=native -E -v - &1 | grep cc1 ... --param l1-cache-size2 --param l1-cache-line-sized --param l2-cache-sizea44 ... $ gcc 4.8.1 -march=native -E -v - &1 | grep cc1 ... --param l1-cache-size=0 --param l1-cache-line-size=0 --param l2-cache-size%6 ... #### Processor 2 #### $ lscpu | grep 'name\|cache' Model name: Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz L1d cache: 32K L1i cache: 32K L2 cache: 256K L3 cache: 8192K $ gcc-4.8.0 -march=native -E -v - &1 | grep cc1 ... --param l1-cache-size2 --param l1-cache-line-sized --param l2-cache-size92 ... $ gcc 4.8.1 -march=native -E -v - &1 | grep cc1 ... --param l1-cache-size=0 --param l1-cache-line-size=0 --param l2-cache-size%6 ... #### Processor 3 #### $ lscpu | grep 'name\|cache' Model name: Intel(R) Core(TM) i3-2330M CPU @ 2.20GHz L1d cache: 32K L1i cache: 32K L2 cache: 256K L3 cache: 3072K $ gcc 4.8.0 -march=native -E -v - &1 | grep cc1 ... --param l1-cache-size2 --param l1-cache-line-sized --param l2-cache-size072 ... $ gcc 4.8.1 -march=native -E -v - &1 | grep cc1 ... --param l1-cache-size=0 --param l1-cache-line-size=0 --param l2-cache-size%6 ... #### GCC version information #### $ gcc-4.8.1 -v Using built-in specs. COLLECT_GCC=gcc-4.8.1 COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.8.1/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../gcc-4.8.1/configure --disable-libssp --disable-multilib --enable-version-specific-runtime-libs --enable-libmudflap --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.8.1 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.1/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.8.1 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.8.1/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.8.1/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.1/include/g++-v4.8 --enable-__cxa_atexit --enable-clocale=gnu --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-ppl --disable-cloog --with-system-zlib --enable-obsolete --disable-werror --enable-secureplt --disable-lto --with-bugurl=http://bugs.funtoo.org --with-pkgversion='Funtoo 4.8.1' --with-mpfr-include=/var/tmp/portage/sys-devel/gcc-4.8.1/work/gcc-4.8.1/mpfr/src --with-mpfr-lib=/var/tmp/portage/sys-devel/gcc-4.8.1/work/objdir/mpfr/src/.libs --enable-libstdcxx-time --enable-libgomp --enable-languages=c,c++,fortran --disable-libgcj --disable-esp Thread model: posix gcc version 4.8.1 (Funtoo 4.8.1) $ gcc-4.8.0 -v Using built-in specs. COLLECT_GCC=gcc-4.8.0 COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.8.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /var/tmp/portage/sys-devel/gcc-4.8.0/work/gcc-4.8.0/configure --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.8.0 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.8.0 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.8.0/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.8.0/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0/include/g++-v4 --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec --disable-fixed-point --with-ppl --with-cloog --disable-isl-version-check --with-cloog --enable-lto --disable-nls --with-system-zlib --enable-obsolete --disable-werror --enable-secureplt --disable-multilib --with-multilib-list=m64 --disable-libmudflap --disable-libssp --enable-libgomp --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.8.0/python --enable-checking=release --disable-libgcj --enable-libstdcxx-time --enable-languages=c,c++,fortran --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-targets=all --with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.8.0 p1.1, pie-0.5.5' Thread model: posix gcc version 4.8.0 (Gentoo 4.8.0 p1.1, pie-0.5.5)