[Bug tree-optimization/68625] New: [6 Regression] Segmentation fault in useless_type_conversion_p

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68625

            Bug ID: 68625
           Summary: [6 Regression] Segmentation fault in
                    useless_type_conversion_p
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---

Created attachment 36875
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36875&action=edit
Testcase

gcc-6.0.0-alpha20151129 for x86_64-pc-linux-gnu segfaults when compiling the
attached (incorrect) testcase at -O2, -O3, or -Ofast.

% x86_64-pc-linux-gnu-gcc-6.0.0-alpha20151129 -w -c -O2 sqyrkevd.c 
sqyrkevd.c: In function 'z9':
sqyrkevd.c:5:1: internal compiler error: Segmentation fault
 z9(void)
 ^~

Partial backtrace:
#0  0x000000000089ad20 in useless_type_conversion_p(tree_node*, tree_node*) ()
#1  0x0000000000cb4b50 in may_propagate_copy(tree_node*, tree_node*) ()
#2  0x0000000000b4e641 in ?? ()
#3  0x000000000071f7f6 in merge_blocks(basic_block_def*, basic_block_def*) ()
#4  0x0000000000b584c6 in ?? ()
#5  0x0000000000b59119 in cleanup_tree_cfg() ()
#6  0x0000000000a41575 in ?? ()
#7  0x0000000000a41fcc in ?? ()
#8  0x0000000000a4487e in execute_one_pass(opt_pass*) ()
#9  0x0000000000a44e38 in ?? ()
#10 0x0000000000a44e4a in ?? ()
#11 0x0000000000a44e4a in ?? ()
#12 0x0000000000a44e95 in execute_pass_list(function*, opt_pass*) ()
#13 0x000000000074e367 in cgraph_node::expand() ()
#14 0x000000000074fcd7 in ?? ()
#15 0x0000000000752323 in symbol_table::finalize_compilation_unit() ()
#16 0x0000000000b0fed2 in ?? ()
#17 0x00000000005ba906 in toplev::main(int, char**) ()
#18 0x00000000005bcb17 in main ()

I cannot reproduce it w/ the same snapshot for target
powerpc-e500v2-linux-gnuspe.