[Bug tree-optimization/56157] [4.8 Regression] ICE with -ftree-vectorize in in compute_live_loop_exits

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56157

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-31 11:09:40 UTC ---
The problematic stmt is placed by:
#0  vect_init_vector_1 (stmt=0x7ffff1abb6e0, new_stmt=0x7ffff1ad6a00, gsi=0x0)
at ../../gcc/tree-vect-stmts.c:1240
#1  0x0000000000c36087 in vect_init_vector (stmt=0x7ffff1abb6e0,
val=0x7ffff1aa3ea0, type=0x7ffff1ace2a0, gsi=0x0)
    at ../../gcc/tree-vect-stmts.c:1310
#2  0x0000000000c649f9 in vect_get_constant_vectors (op=0x7ffff1ac10d8,
slp_node=0x18eb4d0, vec_oprnds=0x18eb470, op_num=0, number_of_vectors=4, 
    reduc_index=-1) at ../../gcc/tree-vect-slp.c:2539
#3  0x0000000000c64f1c in vect_get_slp_defs (ops=..., slp_node=0x18eb4d0,
vec_oprnds=0x7fffffffd750, reduc_index=-1)
    at ../../gcc/tree-vect-slp.c:2696
#4  0x0000000000c3686b in vect_get_vec_defs (op0=0x7ffff1ac10d8,
op1=0x7ffff1ac3c20, stmt=0x7ffff1abb6e0, vec_oprnds0=0x7fffffffd7e0, 
    vec_oprnds1=0x7fffffffd7d0, slp_node=0x18eb4d0, reduc_index=-1) at
../../gcc/tree-vect-stmts.c:1593
#5  0x0000000000c3cc73 in vectorizable_operation (stmt=0x7ffff1abb6e0,
gsi=0x7fffffffda20, vec_stmt=0x7fffffffd980, slp_node=0x18eb4d0)
    at ../../gcc/tree-vect-stmts.c:3728
#6  0x0000000000c43330 in vect_transform_stmt (stmt=0x7ffff1abb6e0,
gsi=0x7fffffffda20, grouped_store=0x7fffffffda3a, slp_node=0x18eb4d0, 
    slp_node_instance=0x18eb8d0) at ../../gcc/tree-vect-stmts.c:5793
#7  0x0000000000c65de3 in vect_schedule_slp_instance (node=0x18eb4d0,
instance=0x18eb8d0, vectorization_factor=4)
    at ../../gcc/tree-vect-slp.c:3095
#8  0x0000000000c659e2 in vect_schedule_slp_instance (node=0x18eb360,
instance=0x18eb8d0, vectorization_factor=4)
    at ../../gcc/tree-vect-slp.c:3020
#9  0x0000000000c659e2 in vect_schedule_slp_instance (node=0x18eb290,
instance=0x18eb8d0, vectorization_factor=4)
    at ../../gcc/tree-vect-slp.c:3020
#10 0x0000000000c659e2 in vect_schedule_slp_instance (node=0x18eafd0,
instance=0x18eb8d0, vectorization_factor=4)
    at ../../gcc/tree-vect-slp.c:3020
#11 0x0000000000c66054 in vect_schedule_slp (loop_vinfo=0x18e1710,
bb_vinfo=0x0) at ../../gcc/tree-vect-slp.c:3165
#12 0x0000000000c5570c in vect_transform_loop (loop_vinfo=0x18e1710) at
../../gcc/tree-vect-loop.c:5693

One thing that might be problematic is that stmt in this case is a pattern
stmt, not original one, but my reading of vect_init_vector_1 shows that
probably it shouldn't make a difference, it only cares about gimple_bb of the
stmt (which should be the same between pattern and original stmt) and some
details from stmt_vinfo (STMT_VINFO_LOOP_VINFO and STMT_VINFO_BB_VINFO should
be the same too, in this case the first one is non-NULL (and not a nested
loop), the latter is NULL).

So, IMHO, either the bug is in vect_get_constant_vectors where it doesn't
supply
non-NULL last argument to vect_init_vector call, or in vect_get_slp_defs.
Given
"For constant and loop invariant defs of SLP_NODE this function returns"...
comment probably not vect_get_constant_vectors fault, the arguments in this
case aren't constant nor loop invariant.
But given:
"Otherwise, the def-stmts must be already vectorized and the vectorized stmts
must be stored in the corresponding child of SLP_NODE, and we call
vect_get_slp_vect_defs () to retrieve them."
the bug might be somewhere earlier too.

Richard, can you please have a look?  Thanks.