http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56573
Bug #: 56573
Summary: GCC generates non-optimal transactional code when
inlining nested transaction.
Classification: Unclassified
Product: gcc
Version: trans-mem
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c
AssignedTo: [email protected]
ReportedBy: [email protected]
Created attachment 29621
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29621
Minimal test case.
GCC generates non-optimal transactional code
when inlining function that has transactional code.
This affects gcc-4.7 and gcc-4.8 (gcc version 4.8.0 20130222 (experimental)).
// example
int a;
static inline void f() {
__transaction_atomic {
++a;
}
}
void g() {
__transaction_atomic {
f();
}
}
void h() {
__transaction_atomic {
__transaction_atomic {
++a;
}
}
}
Generated code:
g():
subq $8, %rsp
movl $41, %edi
xorl %eax, %eax
call _ITM_beginTransaction
movl $41, %edi
xorl %eax, %eax
call _ITM_beginTransaction
movl $a, %edi
call _ITM_RfWU4
leal 1(%rax), %esi
movl $a, %edi
call _ITM_WaWU4
call _ITM_commitTransaction
call _ITM_commitTransaction
addq $8, %rsp
ret
h():
subq $8, %rsp
movl $41, %edi
xorl %eax, %eax
call _ITM_beginTransaction
movl $a, %edi
call _ITM_RfWU4
leal 1(%rax), %esi
movl $a, %edi
call _ITM_WaWU4
call _ITM_commitTransaction
addq $8, %rsp
ret
The bug:
The functions g() and h() should have the __same__ asm.
The problem is that GCC doesn't remove __nested__
_ITM_beginTransaction()/_ITM_commitTransaction
that are known at compile time.
Compiled with:
gcc-4.7 -v -O2 -fgnu-tm -c example.c
Using built-in specs.
COLLECT_GCC=gcc
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.7.2-5ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs
--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.7 --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++/4.7
--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 4.7.2 (Ubuntu/Linaro 4.7.2-5ubuntu1)
COLLECT_GCC_OPTIONS='-v' '-O2' '-fgnu-tm' '-c' '-mtune=generic' '-march=x86-64'
'-pthread'
/usr/lib/gcc/x86_64-linux-gnu/4.7/cc1 -quiet -v -imultiarch x86_64-linux-gnu
-D_REENTRANT example.c -quiet -dumpbase example.c -mtune=generic -march=x86-64
-auxbase example -O2 -version -fgnu-tm -fstack-protector -o /tmp/ccKJdU1H.s
GNU C (Ubuntu/Linaro 4.7.2-5ubuntu1) version 4.7.2 (x86_64-linux-gnu)
compiled by GNU C version 4.7.2, 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
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-linux-gnu/4.7/include
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
GNU C (Ubuntu/Linaro 4.7.2-5ubuntu1) version 4.7.2 (x86_64-linux-gnu)
compiled by GNU C version 4.7.2, 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: fbb4af59dce4dce949ee30395742b8d0
COLLECT_GCC_OPTIONS='-v' '-O2' '-fgnu-tm' '-c' '-mtune=generic' '-march=x86-64'
'-pthread'
as -v --64 -o example.o /tmp/ccKJdU1H.s
GNU assembler version 2.22.90 (x86_64-linux-gnu) using BFD version (GNU
Binutils for Ubuntu) 2.22.90.20120924
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-O2' '-fgnu-tm' '-c' '-mtune=generic' '-march=x86-64'
'-pthread'
