[Bug tree-optimization/46029] -ftree-loop-if-convert-stores causes FAIL: libstdc++-v3/testsuite/ext/pb_ds/example/tree_intervals.cc

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46029

--- Comment #1 from Zdenek Sojka <zsojka at seznam dot cz> 2010-10-15 00:53:15 UTC ---
Created attachment 22048
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22048
hopefully reduced testcase

$ g++ -O -ftree-loop-if-convert-stores pr46029.C
$ ./a.out 
Segmentation fault

In the assembly, with -ftree-loop-if-convert-stores, "nd_it.get_l_child
().get_metadata ()" in apply_update() is loaded unconditionally.

62a64
>       mov     esi, 0  # tmp69,
64,69c66,70
<       mov     rcx, QWORD PTR [rax]    # D.2294, p_nd_32->m_p_left
<       mov     edx, 0  # l_max_endpoint,
<       test    rcx, rcx        # D.2294
<       je      .L3     #,
<       mov     edx, DWORD PTR [rcx+16] # l_max_endpoint, MEM[(unsigned int
&)D.2294_12 + 16]
< .L3:
---
>       mov     rdx, QWORD PTR [rax]    # D.2294, p_nd_32->m_p_left
>       mov     ecx, DWORD PTR [rdx+16] # l_max_endpoint, MEM[(unsigned int &)D.2294_12 + 16]
>       test    rdx, rdx        # D.2294
>       mov     edx, esi        # l_max_endpoint, tmp69
>       cmovne  edx, ecx        # l_max_endpoint,, l_max_endpoint

In the first case, memory is not accessed if the pointer is NULL, but in the
second, "mov ecx, DWORD PTR [rdx+16]" reads invalid memory.