Launchpad has imported 1 comments from the remote bug at http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52574.
If you reply to an imported comment from within Launchpad, your comment will be sent to the remote bug automatically. Read more about Launchpad's inter-bugtracker facilities at https://help.launchpad.net/InterBugTracking. ------------------------------------------------------------------------ On 2012-03-13T01:19:27+00:00 Doko-v wrote: [forwarded from http://bugs.debian.org/663654] The following versions of gcc: Debian gcc-4.6.3-1, Debain gcc-4.4.6-14, Debian gcc-4.6.2-14, Debian gcc-4.4.6-15, Ubuntu 4.4.3-4ubuntu5 generates *wrong* code - aligned vector loads instead of unaligned vector loads for x86_64 arch. This causes the compiled code to crash with SIGSEGV(General Protection Fault). Bug *not* present on trunk and gcc-4.5.3-12. Consider the following program: void foo(int* __restrict ia, int n){ int i; for(i=0;i<n;i++){ ia[i]=ia[i]*ia[i]; } } int main(){ int a[9]; int sum=0,i; for(i=0;i<9;i++){ a[i]=(i*i)%128; } foo((int*)((char*)a+2), 8); for(i=0;i<9;i++){ sum+=a[i]; } return sum; } In x86 and x86_64, unaligned word access are valid - *((int*)<unaligned memory address>) But x86_64 SSE has two kinds of vector instructions - aligned vector move (movdqa) - unaligned vector move (movdqu) Use of aligned vector move with an unaligned vector address, will trigger the application to crash. When compiled with any of the following command lines: gcc -O3 foo.c g++ -O3 foo.c gcc -m64 -O2 -ftree-vectorize gcc_bug.c g++ -m64 -O2 -ftree-vectorize gcc_bug.c gcc generates an aligned vector load movdqa -54(%rsp,%rax), %xmm0 instead of unaligned vector load - movdqu. This result in above application to crash with SIGSEGV(General Protection Fault). gcc-4.7 correctly generates movdqu -54(%rsp), %xmm0 Reply at: https://bugs.launchpad.net/gcc/+bug/953617/comments/0 ** Changed in: gcc-4.6 (Debian) Status: Unknown => New ** Changed in: gcc Status: Unknown => New ** Changed in: gcc Importance: Unknown => Medium -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/953617 Title: gcc tree optimizer generates incorrect vector load instructions for x86_64 To manage notifications about this bug go to: https://bugs.launchpad.net/gcc/+bug/953617/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
