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: unassig...@gcc.gnu.org ReportedBy: srdjan.sti...@gmail.com 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'