[Bug rtl-optimization/47414] New: [4.6 Regression] wrong code with -O -freorder-blocks -fschedule-insns2 -fno-early-inlining -fstrict-aliasing -ftracer

["zsojka at seznam dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47414

           Summary: [4.6 Regression] wrong code with -O -freorder-blocks
                    -fschedule-insns2 -fno-early-inlining
                    -fstrict-aliasing -ftracer
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zsojka@seznam.cz
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu


Created attachment 23077
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23077
reduced testcase

Output:
$ g++ -O -freorder-blocks -fschedule-insns2 -fno-early-inlining
-fstrict-aliasing -ftracer testcase.C
$ ./a.out
==32217== Invalid write of size 8
==32217==    at 0x40061B: test01() (testcase.C:44)
==32217==    by 0x4006BC: main (testcase.C:62)
==32217==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
Segmentation fault

The assembly looks like:
2    mov    rcx, rsp    # nul,
    mov    QWORD PTR [rax], rbp    # b_17->D.2238.next, b
    mov    DWORD PTR [rax+8], 1    # b_17->i,
1    mov    rdx, QWORD PTR [rcx]    # nul, nul_23->D.2238.next
3    mov    QWORD PTR [rsp], rax    # MEM[(struct A *)&s].next, b
    mov    esi, 0    # nul,
    test    rdx, rdx    # nul
    jne    .L10    #,
.L6:
>>>	mov	QWORD PTR [rsi], 0	# nul_12->D.2238.next,
^ crash

The problem is that (1) loads the value before it is stored at (3).
rcx == rsp because of (2).

Without -fschedule-insns2:
    mov    DWORD PTR [rax+8], 1    # b_17->i,
    mov    QWORD PTR [rax], rbp    # b_17->D.2238.next, b
1    mov    QWORD PTR [rsp], rax    # MEM[(struct A *)&s].next, b
    mov    esi, 0    # nul,
2    mov    rcx, rsp    # nul,
3    mov    rdx, QWORD PTR [rcx]    # nul, nul_23->D.2238.next
    test    rdx, rdx    # nul
    jne    .L10    #,
.L6:
    mov    QWORD PTR [rsi], 0    # nul_12->D.2238.next,

The order is correct.

Tested revisions:
r169125 - fail
4.5 r168785 - OK