http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58805
--- Comment #10 from vries at gcc dot gnu.org ---
I've tried out the example from comment 9.
Tree-tail-merge considers the statements without effect because:
...
(gdb) call debug_gimple_stmt (stmt)
# .MEM_10 = VDEF <.MEM_3(D)>
__asm__("movq $42, %0
movq %0, %1
" : "t" "=&r" t_8, "r" "=r" *x_4(D));
(gdb) call gimple_has_side_effects (stmt)
$2 = false
...
and tree-ssa-tail-merge.c:stmt_local_def will return true.
The side effect of the asm is in the expression for the output operand, so
gimple_has_side_effects should return true.
