On Thu, Jun 22, 2017 at 1:30 PM, Richard Sandiford
<richard.sandif...@linaro.org> wrote:
> The test case triggered this assert in vect_update_misalignment_for_peel:
>
> gcc_assert (DR_MISALIGNMENT (dr) / dr_size ==
> DR_MISALIGNMENT (dr_peel) / dr_peel_size);
>
> We knew that the two DRs had the same misalignment at runtime, but when
> considered in isolation, one data reference guaranteed a higher compile-time
> base alignment than the other.
>
> In the test case this looks like a missed opportunity. Both references
> are unconditional, so it should be possible to use the highest of the
> available base alignment guarantees when analyzing each reference.
> The patch does this.
>
> However, as the comment in the patch says, the base alignment guarantees
> provided by a conditional reference only apply if the reference occurs
> at least once. In this case it would be legitimate for two references
> to have the same runtime misalignment and for one reference to provide a
> stronger compile-time guarantee than the other about what the misalignment
> actually is. The patch therefore relaxes the assert to handle that case.
Hmm, but you don't actually check whether a reference occurs only conditional,
do you? You just seem to say that for masked loads/stores the reference
is conditional (I believe that's not true). But for a loop like
for (;;)
if (a[i])
sum += b[j];
you still assume b[j] executes unconditionally?
The vectorizer of course only sees unconditionally executed stmts.
So - I'd simply not add this DR_IS_CONDITIONAL. Did you run into
any real-world (testsuite) issues without this?
Note that the assert is to prevent bogus information. Iff we aligned
DR with base alignment 8 and misalign 3 then if another same-align
DR has base alignment 16 we can't simply zero its DR_MISALIGNMENT
as it still can be 8 after aligning DR.
So I think it's wrong to put DRs with differing base-alignment into
the same-align-refs chain, those should get their DR_MISALIGNMENT
updated independenlty after peeling.
I'd rather not mix fixing this with the improvement to eventuall use a
larger align for the other DR if possible.
Thanks,
Richard.
> Tested on powerpc64-linux-gnu, aarch64-linux-gnu and x86_64-linux-gnu.
> OK to instal?
>
> Richard
>
>
> 2017-06-22 Richard Sandiford <richard.sandif...@linaro.org>
>
> gcc/
> PR tree-optimization/81136
> * tree-vectorizer.h: Include tree-hash-traits.h.
> (vec_base_alignments): New typedef.
> (vec_info): Add a base_alignments field.
> (vect_compute_base_alignments: Declare.
> * tree-data-ref.h (data_reference): Add an is_conditional field.
> (DR_IS_CONDITIONAL): New macro.
> (create_data_ref): Add an is_conditional argument.
> * tree-data-ref.c (create_data_ref): Likewise. Use it to initialize
> the is_conditional field.
> (data_ref_loc): Add an is_conditional field.
> (get_references_in_stmt): Set the is_conditional field.
> (find_data_references_in_stmt): Update call to create_data_ref.
> (graphite_find_data_references_in_stmt): Likewise.
> * tree-ssa-loop-prefetch.c (determine_loop_nest_reuse): Likewise.
> * tree-vect-data-refs.c (vect_analyze_data_refs): Likewise.
> (vect_get_base_address): New function.
> (vect_compute_base_alignments): Likewise.
> (vect_compute_base_alignment): Likewise, split out from...
> (vect_compute_data_ref_alignment): ...here. Use precomputed
> base alignments. Only compute a new base alignment here if the
> reference is conditional.
> (vect_update_misalignment_for_peel): Allow the compile-time
> DR_MISALIGNMENTs of two references with the same runtime alignment
> to be different if one of the references is conditional.
> (vect_find_same_alignment_drs): Compare base addresses instead
> of base objects.
> (vect_compute_data_ref_alignment): Call vect_compute_base_alignments.
> * tree-vect-slp.c (vect_slp_analyze_bb_1): Likewise.
> (new_bb_vec_info): Initialize base_alignments.
> * tree-vect-loop.c (new_loop_vec_info): Likewise.
> * tree-vectorizer.c (vect_destroy_datarefs): Release base_alignments.
>
> gcc/testsuite/
> PR tree-optimization/81136
> * gcc.dg/vect/pr81136.c: New test.
>
> Index: gcc/tree-vectorizer.h
> ===================================================================
> --- gcc/tree-vectorizer.h 2017-06-08 08:51:43.347264181 +0100
> +++ gcc/tree-vectorizer.h 2017-06-22 12:23:21.288421018 +0100
> @@ -22,6 +22,7 @@ Software Foundation; either version 3, o
> #define GCC_TREE_VECTORIZER_H
>
> #include "tree-data-ref.h"
> +#include "tree-hash-traits.h"
> #include "target.h"
>
> /* Used for naming of new temporaries. */
> @@ -84,6 +85,10 @@ struct stmt_info_for_cost {
>
> typedef vec<stmt_info_for_cost> stmt_vector_for_cost;
>
> +/* Maps base addresses to the largest alignment that we've been able
> + to calculate for them. */
> +typedef hash_map<tree_operand_hash, unsigned int> vec_base_alignments;
> +
> /************************************************************************
> SLP
> ************************************************************************/
> @@ -156,6 +161,10 @@ struct vec_info {
> /* All data references. */
> vec<data_reference_p> datarefs;
>
> + /* Maps the base addresses of all data references in DATAREFS to the
> + largest alignment that we've been able to calculate for them. */
> + vec_base_alignments base_alignments;
> +
> /* All data dependences. */
> vec<ddr_p> ddrs;
>
> @@ -1117,6 +1126,7 @@ extern bool vect_prune_runtime_alias_tes
> extern bool vect_check_gather_scatter (gimple *, loop_vec_info,
> gather_scatter_info *);
> extern bool vect_analyze_data_refs (vec_info *, int *);
> +extern void vect_compute_base_alignments (vec_info *);
> extern tree vect_create_data_ref_ptr (gimple *, tree, struct loop *, tree,
> tree *, gimple_stmt_iterator *,
> gimple **, bool, bool *,
> Index: gcc/tree-data-ref.h
> ===================================================================
> --- gcc/tree-data-ref.h 2017-06-08 08:51:43.349263895 +0100
> +++ gcc/tree-data-ref.h 2017-06-22 12:23:21.285421180 +0100
> @@ -119,6 +119,10 @@ struct data_reference
> /* True when the data reference is in RHS of a stmt. */
> bool is_read;
>
> + /* True when the data reference is conditional, i.e. if it might not
> + occur even when the statement runs to completion. */
> + bool is_conditional;
> +
> /* Behavior of the memory reference in the innermost loop. */
> struct innermost_loop_behavior innermost;
>
> @@ -138,6 +142,7 @@ #define DR_ACCESS_FN(DR, I) DR_AC
> #define DR_NUM_DIMENSIONS(DR) DR_ACCESS_FNS (DR).length ()
> #define DR_IS_READ(DR) (DR)->is_read
> #define DR_IS_WRITE(DR) (!DR_IS_READ (DR))
> +#define DR_IS_CONDITIONAL(DR) (DR)->is_conditional
> #define DR_BASE_ADDRESS(DR) (DR)->innermost.base_address
> #define DR_OFFSET(DR) (DR)->innermost.offset
> #define DR_INIT(DR) (DR)->innermost.init
> @@ -350,7 +355,8 @@ extern bool graphite_find_data_reference
> vec<data_reference_p> *);
> tree find_data_references_in_loop (struct loop *, vec<data_reference_p> *);
> bool loop_nest_has_data_refs (loop_p loop);
> -struct data_reference *create_data_ref (loop_p, loop_p, tree, gimple *,
> bool);
> +struct data_reference *create_data_ref (loop_p, loop_p, tree, gimple *, bool,
> + bool);
> extern bool find_loop_nest (struct loop *, vec<loop_p> *);
> extern struct data_dependence_relation *initialize_data_dependence_relation
> (struct data_reference *, struct data_reference *, vec<loop_p>);
> Index: gcc/tree-data-ref.c
> ===================================================================
> --- gcc/tree-data-ref.c 2017-06-08 08:51:43.349263895 +0100
> +++ gcc/tree-data-ref.c 2017-06-22 12:23:21.284421233 +0100
> @@ -1053,15 +1053,18 @@ free_data_ref (data_reference_p dr)
> free (dr);
> }
>
> -/* Analyzes memory reference MEMREF accessed in STMT. The reference
> - is read if IS_READ is true, write otherwise. Returns the
> - data_reference description of MEMREF. NEST is the outermost loop
> - in which the reference should be instantiated, LOOP is the loop in
> - which the data reference should be analyzed. */
> +/* Analyze memory reference MEMREF, which is accessed in STMT. The reference
> + is a read if IS_READ is true, otherwise it is a write. IS_CONDITIONAL
> + indicates that the reference is conditional, i.e. that it might not
> + occur every time that STMT runs to completion.
> +
> + Return the data_reference description of MEMREF. NEST is the outermost
> + loop in which the reference should be instantiated, LOOP is the loop
> + in which the data reference should be analyzed. */
>
> struct data_reference *
> create_data_ref (loop_p nest, loop_p loop, tree memref, gimple *stmt,
> - bool is_read)
> + bool is_read, bool is_conditional)
> {
> struct data_reference *dr;
>
> @@ -1076,6 +1079,7 @@ create_data_ref (loop_p nest, loop_p loo
> DR_STMT (dr) = stmt;
> DR_REF (dr) = memref;
> DR_IS_READ (dr) = is_read;
> + DR_IS_CONDITIONAL (dr) = is_conditional;
>
> dr_analyze_innermost (dr, nest);
> dr_analyze_indices (dr, nest, loop);
> @@ -4446,6 +4450,10 @@ struct data_ref_loc
>
> /* True if the memory reference is read. */
> bool is_read;
> +
> + /* True if the data reference is conditional, i.e. if it might not
> + occur even when the statement runs to completion. */
> + bool is_conditional;
> };
>
>
> @@ -4512,6 +4520,7 @@ get_references_in_stmt (gimple *stmt, ve
> {
> ref.ref = op1;
> ref.is_read = true;
> + ref.is_conditional = false;
> references->safe_push (ref);
> }
> }
> @@ -4539,6 +4548,7 @@ get_references_in_stmt (gimple *stmt, ve
> type = TREE_TYPE (gimple_call_arg (stmt, 3));
> if (TYPE_ALIGN (type) != align)
> type = build_aligned_type (type, align);
> + ref.is_conditional = true;
> ref.ref = fold_build2 (MEM_REF, type, gimple_call_arg (stmt, 0),
> ptr);
> references->safe_push (ref);
> @@ -4558,6 +4568,7 @@ get_references_in_stmt (gimple *stmt, ve
> {
> ref.ref = op1;
> ref.is_read = true;
> + ref.is_conditional = false;
> references->safe_push (ref);
> }
> }
> @@ -4571,6 +4582,7 @@ get_references_in_stmt (gimple *stmt, ve
> {
> ref.ref = op0;
> ref.is_read = false;
> + ref.is_conditional = false;
> references->safe_push (ref);
> }
> return clobbers_memory;
> @@ -4635,8 +4647,8 @@ find_data_references_in_stmt (struct loo
>
> FOR_EACH_VEC_ELT (references, i, ref)
> {
> - dr = create_data_ref (nest, loop_containing_stmt (stmt),
> - ref->ref, stmt, ref->is_read);
> + dr = create_data_ref (nest, loop_containing_stmt (stmt), ref->ref,
> + stmt, ref->is_read, ref->is_conditional);
> gcc_assert (dr != NULL);
> datarefs->safe_push (dr);
> }
> @@ -4665,7 +4677,8 @@ graphite_find_data_references_in_stmt (l
>
> FOR_EACH_VEC_ELT (references, i, ref)
> {
> - dr = create_data_ref (nest, loop, ref->ref, stmt, ref->is_read);
> + dr = create_data_ref (nest, loop, ref->ref, stmt, ref->is_read,
> + ref->is_conditional);
> gcc_assert (dr != NULL);
> datarefs->safe_push (dr);
> }
> Index: gcc/tree-ssa-loop-prefetch.c
> ===================================================================
> --- gcc/tree-ssa-loop-prefetch.c 2017-06-07 21:58:55.928557601 +0100
> +++ gcc/tree-ssa-loop-prefetch.c 2017-06-22 12:23:21.285421180 +0100
> @@ -1633,7 +1633,7 @@ determine_loop_nest_reuse (struct loop *
> for (ref = gr->refs; ref; ref = ref->next)
> {
> dr = create_data_ref (nest, loop_containing_stmt (ref->stmt),
> - ref->mem, ref->stmt, !ref->write_p);
> + ref->mem, ref->stmt, !ref->write_p, false);
>
> if (dr)
> {
> Index: gcc/tree-vect-data-refs.c
> ===================================================================
> --- gcc/tree-vect-data-refs.c 2017-06-08 08:51:43.350263752 +0100
> +++ gcc/tree-vect-data-refs.c 2017-06-22 12:23:21.286421126 +0100
> @@ -646,6 +646,102 @@ vect_slp_analyze_instance_dependence (sl
> return res;
> }
>
> +/* If DR is nested in a loop that is being vectorized, return the base
> + address in the context of the vectorized loop (rather than the
> + nested loop). Otherwise return the base address in the context
> + of the containing statement. */
> +
> +static tree
> +vect_get_base_address (data_reference *dr)
> +{
> + gimple *stmt = DR_STMT (dr);
> + stmt_vec_info stmt_info = vinfo_for_stmt (stmt);
> + loop_vec_info loop_vinfo = STMT_VINFO_LOOP_VINFO (stmt_info);
> + struct loop *loop = loop_vinfo != NULL ? LOOP_VINFO_LOOP (loop_vinfo) :
> NULL;
> + if (loop && nested_in_vect_loop_p (loop, stmt))
> + return STMT_VINFO_DR_BASE_ADDRESS (stmt_info);
> + else
> + return DR_BASE_ADDRESS (dr);
> +}
> +
> +/* Compute and return the alignment of base address BASE_ADDR in DR. */
> +
> +static unsigned int
> +vect_compute_base_alignment (data_reference *dr, tree base_addr)
> +{
> + /* To look at the alignment of the base we have to preserve an inner
> + MEM_REF as that carries the alignment information of the actual
> + access. */
> + tree base = DR_REF (dr);
> + while (handled_component_p (base))
> + base = TREE_OPERAND (base, 0);
> + unsigned int base_alignment = 0;
> + unsigned HOST_WIDE_INT base_bitpos;
> + get_object_alignment_1 (base, &base_alignment, &base_bitpos);
> +
> + /* As data-ref analysis strips the MEM_REF down to its base operand
> + to form DR_BASE_ADDRESS and adds the offset to DR_INIT we have to
> + adjust things to make base_alignment valid as the alignment of
> + DR_BASE_ADDRESS. */
> + if (TREE_CODE (base) == MEM_REF)
> + {
> + /* Note all this only works if DR_BASE_ADDRESS is the same as
> + MEM_REF operand zero, otherwise DR/SCEV analysis might have factored
> + in other offsets. We need to rework DR to compute the alingment
> + of DR_BASE_ADDRESS as long as all information is still available. */
> + if (operand_equal_p (TREE_OPERAND (base, 0), base_addr, 0))
> + {
> + base_bitpos -= mem_ref_offset (base).to_short_addr () *
> BITS_PER_UNIT;
> + base_bitpos &= (base_alignment - 1);
> + }
> + else
> + base_bitpos = BITS_PER_UNIT;
> + }
> + if (base_bitpos != 0)
> + base_alignment = base_bitpos & -base_bitpos;
> +
> + /* Also look at the alignment of the base address DR analysis
> + computed. */
> + unsigned int base_addr_alignment = get_pointer_alignment (base_addr);
> + if (base_addr_alignment > base_alignment)
> + base_alignment = base_addr_alignment;
> +
> + return base_alignment;
> +}
> +
> +/* Compute alignments for the base addresses of all datarefs in VINFO. */
> +
> +void
> +vect_compute_base_alignments (vec_info *vinfo)
> +{
> + /* If the region we're going to vectorize is reached, all unconditional
> + data references occur at least once. We can therefore pool the base
> + alignment guarantees from each unconditional reference. */
> + data_reference *dr;
> + unsigned int i;
> + FOR_EACH_VEC_ELT (vinfo->datarefs, i, dr)
> + if (!DR_IS_CONDITIONAL (dr))
> + {
> + tree base_addr = vect_get_base_address (dr);
> + unsigned int alignment = vect_compute_base_alignment (dr, base_addr);
> + bool existed;
> + unsigned int &entry
> + = vinfo->base_alignments.get_or_insert (base_addr, &existed);
> + if (!existed || entry < alignment)
> + {
> + entry = alignment;
> + if (dump_enabled_p ())
> + {
> + dump_printf_loc (MSG_NOTE, vect_location,
> + "setting base alignment for ");
> + dump_generic_expr (MSG_NOTE, TDF_SLIM, base_addr);
> + dump_printf (MSG_NOTE, " to %d, based on ", alignment);
> + dump_gimple_stmt (MSG_NOTE, TDF_SLIM, DR_STMT (dr), 0);
> + }
> + }
> + }
> +}
> +
> /* Function vect_compute_data_ref_alignment
>
> Compute the misalignment of the data reference DR.
> @@ -663,6 +759,7 @@ vect_compute_data_ref_alignment (struct
> {
> gimple *stmt = DR_STMT (dr);
> stmt_vec_info stmt_info = vinfo_for_stmt (stmt);
> + vec_base_alignments *base_alignments = &stmt_info->vinfo->base_alignments;
> loop_vec_info loop_vinfo = STMT_VINFO_LOOP_VINFO (stmt_info);
> struct loop *loop = NULL;
> tree ref = DR_REF (dr);
> @@ -699,6 +796,8 @@ vect_compute_data_ref_alignment (struct
> {
> tree step = DR_STEP (dr);
>
> + base_addr = STMT_VINFO_DR_BASE_ADDRESS (stmt_info);
> + aligned_to = STMT_VINFO_DR_ALIGNED_TO (stmt_info);
> if (tree_fits_shwi_p (step)
> && tree_to_shwi (step) % GET_MODE_SIZE (TYPE_MODE (vectype)) == 0)
> {
> @@ -706,8 +805,6 @@ vect_compute_data_ref_alignment (struct
> dump_printf_loc (MSG_NOTE, vect_location,
> "inner step divides the vector-size.\n");
> misalign = STMT_VINFO_DR_INIT (stmt_info);
> - aligned_to = STMT_VINFO_DR_ALIGNED_TO (stmt_info);
> - base_addr = STMT_VINFO_DR_BASE_ADDRESS (stmt_info);
> }
> else
> {
> @@ -738,39 +835,15 @@ vect_compute_data_ref_alignment (struct
> }
> }
>
> - /* To look at alignment of the base we have to preserve an inner MEM_REF
> - as that carries alignment information of the actual access. */
> - base = ref;
> - while (handled_component_p (base))
> - base = TREE_OPERAND (base, 0);
> + /* Calculate the maximum of the pooled base address alignment and the
> + alignment that we can compute for DR itself. The latter should
> + already be included in the former for unconditional references. */
> unsigned int base_alignment = 0;
> - unsigned HOST_WIDE_INT base_bitpos;
> - get_object_alignment_1 (base, &base_alignment, &base_bitpos);
> - /* As data-ref analysis strips the MEM_REF down to its base operand
> - to form DR_BASE_ADDRESS and adds the offset to DR_INIT we have to
> - adjust things to make base_alignment valid as the alignment of
> - DR_BASE_ADDRESS. */
> - if (TREE_CODE (base) == MEM_REF)
> - {
> - /* Note all this only works if DR_BASE_ADDRESS is the same as
> - MEM_REF operand zero, otherwise DR/SCEV analysis might have factored
> - in other offsets. We need to rework DR to compute the alingment
> - of DR_BASE_ADDRESS as long as all information is still available. */
> - if (operand_equal_p (TREE_OPERAND (base, 0), base_addr, 0))
> - {
> - base_bitpos -= mem_ref_offset (base).to_short_addr () *
> BITS_PER_UNIT;
> - base_bitpos &= (base_alignment - 1);
> - }
> - else
> - base_bitpos = BITS_PER_UNIT;
> - }
> - if (base_bitpos != 0)
> - base_alignment = base_bitpos & -base_bitpos;
> - /* Also look at the alignment of the base address DR analysis
> - computed. */
> - unsigned int base_addr_alignment = get_pointer_alignment (base_addr);
> - if (base_addr_alignment > base_alignment)
> - base_alignment = base_addr_alignment;
> + if (DR_IS_CONDITIONAL (dr))
> + base_alignment = vect_compute_base_alignment (dr, base_addr);
> + if (unsigned int *entry = base_alignments->get (base_addr))
> + base_alignment = MAX (base_alignment, *entry);
> + gcc_assert (base_alignment != 0);
>
> if (base_alignment >= TYPE_ALIGN (TREE_TYPE (vectype)))
> DR_VECT_AUX (dr)->base_element_aligned = true;
> @@ -906,8 +979,29 @@ vect_update_misalignment_for_peel (struc
> {
> if (current_dr != dr)
> continue;
> - gcc_assert (DR_MISALIGNMENT (dr) / dr_size ==
> - DR_MISALIGNMENT (dr_peel) / dr_peel_size);
> + /* Any alignment guarantees provided by a reference only apply if
> + the reference actually occurs. For example, in:
> +
> + struct s __attribute__((aligned(32))) {
> + int misaligner;
> + int array[N];
> + };
> +
> + int *ptr;
> + for (int i = 0; i < n; ++i)
> + ptr[i] = c[i] ? ((struct s *) (ptr - 1))->array[i] : 0;
> +
> + we can only assume that ptr is part of a struct s if at least one
> + c[i] is true. This in turn means that we have a higher base
> + alignment guarantee for the read from ptr (if it occurs) than for
> + the write to ptr, and we cannot unconditionally carry the former
> + over to the latter. We still know that the two address values
> + have the same misalignment, so if peeling has forced one of them
> + to be aligned, the other must be too. */
> + gcc_assert (DR_IS_CONDITIONAL (dr_peel)
> + || DR_IS_CONDITIONAL (dr)
> + || (DR_MISALIGNMENT (dr) / dr_size
> + == DR_MISALIGNMENT (dr_peel) / dr_peel_size));
> SET_DR_MISALIGNMENT (dr, 0);
> return;
> }
> @@ -2117,8 +2211,7 @@ vect_find_same_alignment_drs (struct dat
> if (dra == drb)
> return;
>
> - if (!operand_equal_p (DR_BASE_OBJECT (dra), DR_BASE_OBJECT (drb),
> - OEP_ADDRESS_OF)
> + if (!operand_equal_p (DR_BASE_ADDRESS (dra), DR_BASE_ADDRESS (drb), 0)
> || !operand_equal_p (DR_OFFSET (dra), DR_OFFSET (drb), 0)
> || !operand_equal_p (DR_STEP (dra), DR_STEP (drb), 0))
> return;
> @@ -2176,6 +2269,7 @@ vect_analyze_data_refs_alignment (loop_v
> vec<data_reference_p> datarefs = vinfo->datarefs;
> struct data_reference *dr;
>
> + vect_compute_base_alignments (vinfo);
> FOR_EACH_VEC_ELT (datarefs, i, dr)
> {
> stmt_vec_info stmt_info = vinfo_for_stmt (DR_STMT (dr));
> @@ -3374,7 +3468,8 @@ vect_analyze_data_refs (vec_info *vinfo,
> {
> struct data_reference *newdr
> = create_data_ref (NULL, loop_containing_stmt (stmt),
> - DR_REF (dr), stmt, maybe_scatter ? false :
> true);
> + DR_REF (dr), stmt, !maybe_scatter,
> + DR_IS_CONDITIONAL (dr));
> gcc_assert (newdr != NULL && DR_REF (newdr));
> if (DR_BASE_ADDRESS (newdr)
> && DR_OFFSET (newdr)
> Index: gcc/tree-vect-slp.c
> ===================================================================
> --- gcc/tree-vect-slp.c 2017-06-07 21:58:56.336475882 +0100
> +++ gcc/tree-vect-slp.c 2017-06-22 12:23:21.288421018 +0100
> @@ -2367,6 +2367,7 @@ new_bb_vec_info (gimple_stmt_iterator re
> gimple_stmt_iterator gsi;
>
> res = (bb_vec_info) xcalloc (1, sizeof (struct _bb_vec_info));
> + new (&res->base_alignments) vec_base_alignments ();
> res->kind = vec_info::bb;
> BB_VINFO_BB (res) = bb;
> res->region_begin = region_begin;
> @@ -2741,6 +2742,8 @@ vect_slp_analyze_bb_1 (gimple_stmt_itera
> return NULL;
> }
>
> + vect_compute_base_alignments (bb_vinfo);
> +
> /* Analyze and verify the alignment of data references and the
> dependence in the SLP instances. */
> for (i = 0; BB_VINFO_SLP_INSTANCES (bb_vinfo).iterate (i, &instance); )
> Index: gcc/tree-vect-loop.c
> ===================================================================
> --- gcc/tree-vect-loop.c 2017-06-22 12:22:57.734313143 +0100
> +++ gcc/tree-vect-loop.c 2017-06-22 12:23:21.287421072 +0100
> @@ -1157,6 +1157,7 @@ new_loop_vec_info (struct loop *loop)
> LOOP_VINFO_VECT_FACTOR (res) = 0;
> LOOP_VINFO_LOOP_NEST (res) = vNULL;
> LOOP_VINFO_DATAREFS (res) = vNULL;
> + new (&res->base_alignments) vec_base_alignments ();
> LOOP_VINFO_DDRS (res) = vNULL;
> LOOP_VINFO_UNALIGNED_DR (res) = NULL;
> LOOP_VINFO_MAY_MISALIGN_STMTS (res) = vNULL;
> Index: gcc/tree-vectorizer.c
> ===================================================================
> --- gcc/tree-vectorizer.c 2017-06-22 12:22:57.732313220 +0100
> +++ gcc/tree-vectorizer.c 2017-06-22 12:23:21.288421018 +0100
> @@ -370,6 +370,8 @@ vect_destroy_datarefs (vec_info *vinfo)
> }
>
> free_data_refs (vinfo->datarefs);
> +
> + vinfo->base_alignments.~vec_base_alignments ();
> }
>
> /* A helper function to free scev and LOOP niter information, as well as
> Index: gcc/testsuite/gcc.dg/vect/pr81136.c
> ===================================================================
> --- /dev/null 2017-06-22 07:43:14.805493307 +0100
> +++ gcc/testsuite/gcc.dg/vect/pr81136.c 2017-06-22 12:23:21.283421287 +0100
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +
> +struct __attribute__((aligned (32)))
> +{
> + char misaligner;
> + int foo[100];
> + int bar[100];
> +} *a;
> +
> +void
> +fn1 (int n)
> +{
> + int *b = a->foo;
> + for (int i = 0; i < n; i++)
> + a->bar[i] = b[i];
> +}
