https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66875
Bug ID: 66875
Summary: entire for loop got eliminated at cddce2 tree-opt
stage
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: patricksung at gmail dot com
Target Milestone: ---
Created attachment 35985
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35985&action=edit
Intermediate of the C source
Hi the attached code in the parse_peppi_protocol() (which got inline into
parse()) with the for loop (and nearby code) from line 10821 to line 10995 got
eliminated.
We found out this problem starting with GCC version 4.9.2 and subsequently also
tested with GCC 4.9.3 and 5.1 also having this problem.
One of the following two ways will work around this problem,
1) -fno-aggressive-loop-optimizations (obvious?)
2) change the for loop code from "for (...; i++)" to "for (...; --i)", i.e. the
loop search backwards.
We also found that the code elimination was happening at the "cddce2" stage of
the tree optimization. Here is the command line used with the -v output (with
compiler warnings removed that I believe is irrelevant to this problem to make
the output a little bit cleaner here)
x86_64-peplink-linux-gnu-gcc -D_LARGEFILE_SOURCE=1 -D_LARGE_FILES
-D_FILE_OFFSET_BITS=64 -D_REENTRANT -DXTABLES_LIBDIR=\"/usr/lib/xtables\"
-DXTABLES_INTERNAL -I../include -I.. -I../include
-I/home/psung/tmp/fw.63.ndpi-test/staging/usr/include
-I/home/psung/tmp/fw.63.ndpi-test/staging/usr/include
-Wp,-MMD,./.libxt_peppi.oo.d,-MT,libxt_peppi.oo -Wall -Waggregate-return
-Wmissing-declarations -Wmissing-prototypes -Wredundant-decls -Wshadow
-Wstrict-prototypes -Winline -pipe -D_INIT=libxt_peppi_init -DPIC -fPIC
-Wextra -g -O3 -o libxt_peppi.oo -c libxt_peppi.c -dp -save-temps
-fdump-tree-cddce2-details-stats -fno-strict-aliasing -fwrapv -v
x86_64-peplink-linux-gnu-gcc: warning: -pipe ignored because -save-temps
specified
Using built-in specs.
COLLECT_GCC=x86_64-peplink-linux-gnu-gcc
Target: x86_64-peplink-linux-gnu
Configured with:
/home/psung/toolchains-2015/x64-4.9.3/.build/src/gcc-4.9.3/configure
--build=x86_64-build_unknown-linux-gnu --host=x86_64-build_unknown-linux-gnu
--target=x86_64-peplink-linux-gnu
--prefix=/home/psung/x-tools-2015/x86_64-peplink-linux-gnu
--with-sysroot=/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/x86_64-peplink-linux-gnu/sysroot
--enable-languages=c,c++,go --with-pkgversion='crosstool-NG
crosstool-ng-1.21.0-50-g488f7a8' --enable-__cxa_atexit --disable-libmudflap
--disable-libgomp --disable-libssp --disable-libquadmath
--disable-libquadmath-support --disable-libsanitizer
--with-gmp=/home/psung/toolchains-2015/x64-4.9.3/.build/x86_64-peplink-linux-gnu/buildtools
--with-mpfr=/home/psung/toolchains-2015/x64-4.9.3/.build/x86_64-peplink-linux-gnu/buildtools
--with-mpc=/home/psung/toolchains-2015/x64-4.9.3/.build/x86_64-peplink-linux-gnu/buildtools
--with-ppl=no --with-isl=no --with-cloog=no
--with-libelf=/home/psung/toolchains-2015/x64-4.9.3/.build/x86_64-peplink-linux-gnu/buildtools
--with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm'
--enable-threads=posix --enable-gold --disable-nls --disable-multilib
--with-local-prefix=/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/x86_64-peplink-linux-gnu/sysroot
--enable-long-long
Thread model: posix
gcc version 4.9.3 (crosstool-NG crosstool-ng-1.21.0-50-g488f7a8)
COLLECT_GCC_OPTIONS='-D' '_LARGEFILE_SOURCE=1' '-D' '_LARGE_FILES' '-D'
'_FILE_OFFSET_BITS=64' '-D' '_REENTRANT' '-D'
'XTABLES_LIBDIR="/usr/lib/xtables"' '-D' 'XTABLES_INTERNAL' '-I' '../include'
'-I' '..' '-I' '../include' '-I'
'/home/psung/tmp/fw.63.ndpi-test/staging/usr/include' '-I'
'/home/psung/tmp/fw.63.ndpi-test/staging/usr/include' '-Wall'
'-Waggregate-return' '-Wmissing-declarations' '-Wmissing-prototypes'
'-Wredundant-decls' '-Wshadow' '-Wstrict-prototypes' '-Winline' '-pipe' '-D'
'_INIT=libxt_peppi_init' '-D' 'PIC' '-fPIC' '-Wextra' '-g' '-O3' '-o'
'libxt_peppi.oo' '-c' '-dp' '-save-temps' '-fdump-tree-cddce2-details-stats'
'-fno-strict-aliasing' '-fwrapv' '-v' '-mtune=generic' '-march=x86-64'
/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/libexec/gcc/x86_64-peplink-linux-gnu/4.9.3/cc1
-E -quiet -v -I ../include -I .. -I ../include -I
/home/psung/tmp/fw.63.ndpi-test/staging/usr/include -I
/home/psung/tmp/fw.63.ndpi-test/staging/usr/include -D _LARGEFILE_SOURCE=1 -D
_LARGE_FILES -D _FILE_OFFSET_BITS=64 -D _REENTRANT -D
XTABLES_LIBDIR="/usr/lib/xtables" -D XTABLES_INTERNAL -D _INIT=libxt_peppi_init
-D PIC -MMD ./.libxt_peppi.oo.d -MT libxt_peppi.oo libxt_peppi.c -mtune=generic
-march=x86-64 -Wall -Waggregate-return -Wmissing-declarations
-Wmissing-prototypes -Wredundant-decls -Wshadow -Wstrict-prototypes -Winline
-Wextra -fPIC -fdump-tree-cddce2-details-stats -fno-strict-aliasing -fwrapv -g
-fworking-directory -O3 -fpch-preprocess -o libxt_peppi.i
ignoring nonexistent directory
"/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/x86_64-peplink-linux-gnu/sysroot/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/x86_64-peplink-linux-gnu/sysroot/include"
ignoring duplicate directory "../include"
ignoring duplicate directory
"/home/psung/tmp/fw.63.ndpi-test/staging/usr/include"
#include "..." search starts here:
#include <...> search starts here:
../include
..
/home/psung/tmp/fw.63.ndpi-test/staging/usr/include
/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/4.9.3/include
/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/4.9.3/include-fixed
/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/4.9.3/../../../../x86_64-peplink-linux-gnu/include
/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/x86_64-peplink-linux-gnu/sysroot/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-D' '_LARGEFILE_SOURCE=1' '-D' '_LARGE_FILES' '-D'
'_FILE_OFFSET_BITS=64' '-D' '_REENTRANT' '-D'
'XTABLES_LIBDIR="/usr/lib/xtables"' '-D' 'XTABLES_INTERNAL' '-I' '../include'
'-I' '..' '-I' '../include' '-I'
'/home/psung/tmp/fw.63.ndpi-test/staging/usr/include' '-I'
'/home/psung/tmp/fw.63.ndpi-test/staging/usr/include' '-Wall'
'-Waggregate-return' '-Wmissing-declarations' '-Wmissing-prototypes'
'-Wredundant-decls' '-Wshadow' '-Wstrict-prototypes' '-Winline' '-pipe' '-D'
'_INIT=libxt_peppi_init' '-D' 'PIC' '-fPIC' '-Wextra' '-g' '-O3' '-o'
'libxt_peppi.oo' '-c' '-dp' '-save-temps' '-fdump-tree-cddce2-details-stats'
'-fno-strict-aliasing' '-fwrapv' '-v' '-mtune=generic' '-march=x86-64'
/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/libexec/gcc/x86_64-peplink-linux-gnu/4.9.3/cc1
-fpreprocessed libxt_peppi.i -quiet -dumpbase libxt_peppi.c -dp -mtune=generic
-march=x86-64 -auxbase-strip libxt_peppi.oo -g -O3 -Wall -Waggregate-return
-Wmissing-declarations -Wmissing-prototypes -Wredundant-decls -Wshadow
-Wstrict-prototypes -Winline -Wextra -version -fPIC
-fdump-tree-cddce2-details-stats -fno-strict-aliasing -fwrapv -o libxt_peppi.s
GNU C (crosstool-NG crosstool-ng-1.21.0-50-g488f7a8) version 4.9.3
(x86_64-peplink-linux-gnu)
compiled by GNU C version 4.7.3, GMP version 6.0.0, MPFR version 3.1.2,
MPC version 1.0.2
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C (crosstool-NG crosstool-ng-1.21.0-50-g488f7a8) version 4.9.3
(x86_64-peplink-linux-gnu)
compiled by GNU C version 4.7.3, GMP version 6.0.0, MPFR version 3.1.2,
MPC version 1.0.2
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: a9b782f9952f9abb8547d3239b6bb751
^
COLLECT_GCC_OPTIONS='-D' '_LARGEFILE_SOURCE=1' '-D' '_LARGE_FILES' '-D'
'_FILE_OFFSET_BITS=64' '-D' '_REENTRANT' '-D'
'XTABLES_LIBDIR="/usr/lib/xtables"' '-D' 'XTABLES_INTERNAL' '-I' '../include'
'-I' '..' '-I' '../include' '-I'
'/home/psung/tmp/fw.63.ndpi-test/staging/usr/include' '-I'
'/home/psung/tmp/fw.63.ndpi-test/staging/usr/include' '-Wall'
'-Waggregate-return' '-Wmissing-declarations' '-Wmissing-prototypes'
'-Wredundant-decls' '-Wshadow' '-Wstrict-prototypes' '-Winline' '-pipe' '-D'
'_INIT=libxt_peppi_init' '-D' 'PIC' '-fPIC' '-Wextra' '-g' '-O3' '-o'
'libxt_peppi.oo' '-c' '-dp' '-save-temps' '-fdump-tree-cddce2-details-stats'
'-fno-strict-aliasing' '-fwrapv' '-v' '-mtune=generic' '-march=x86-64'
/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/4.9.3/../../../../x86_64-peplink-linux-gnu/bin/as
-v -I ../include -I .. -I ../include -I
/home/psung/tmp/fw.63.ndpi-test/staging/usr/include -I
/home/psung/tmp/fw.63.ndpi-test/staging/usr/include --64 -o libxt_peppi.oo
libxt_peppi.s
GNU assembler version 2.24 (x86_64-peplink-linux-gnu) using BFD version
(crosstool-NG crosstool-ng-1.21.0-50-g488f7a8) 2.24
COMPILER_PATH=/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/libexec/gcc/x86_64-peplink-linux-gnu/4.9.3/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/libexec/gcc/x86_64-peplink-linux-gnu/4.9.3/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/libexec/gcc/x86_64-peplink-linux-gnu/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/4.9.3/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/4.9.3/../../../../x86_64-peplink-linux-gnu/bin/
LIBRARY_PATH=/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/4.9.3/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/4.9.3/../../../../x86_64-peplink-linux-gnu/lib/../lib64/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/x86_64-peplink-linux-gnu/sysroot/lib/../lib64/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/x86_64-peplink-linux-gnu/sysroot/usr/lib/../lib64/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/lib/gcc/x86_64-peplink-linux-gnu/4.9.3/../../../../x86_64-peplink-linux-gnu/lib/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/x86_64-peplink-linux-gnu/sysroot/lib/:/home/psung/x-tools-2015/x86_64-peplink-linux-gnu/x86_64-peplink-linux-gnu/sysroot/usr/lib/
COLLECT_GCC_OPTIONS='-D' '_LARGEFILE_SOURCE=1' '-D' '_LARGE_FILES' '-D'
'_FILE_OFFSET_BITS=64' '-D' '_REENTRANT' '-D'
'XTABLES_LIBDIR="/usr/lib/xtables"' '-D' 'XTABLES_INTERNAL' '-I' '../include'
'-I' '..' '-I' '../include' '-I'
'/home/psung/tmp/fw.63.ndpi-test/staging/usr/include' '-I'
'/home/psung/tmp/fw.63.ndpi-test/staging/usr/include' '-Wall'
'-Waggregate-return' '-Wmissing-declarations' '-Wmissing-prototypes'
'-Wredundant-decls' '-Wshadow' '-Wstrict-prototypes' '-Winline' '-pipe' '-D'
'_INIT=libxt_peppi_init' '-D' 'PIC' '-fPIC' '-Wextra' '-g' '-O3' '-o'
'libxt_peppi.oo' '-c' '-dp' '-save-temps' '-fdump-tree-cddce2-details-stats'
'-fno-strict-aliasing' '-fwrapv' '-v' '-mtune=generic' '-march=x86-64'
