On Mon, Jun 26, 2017 at 12:25 PM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Fri, Jun 23, 2017 at 2:05 PM, Richard Sandiford
> <richard.sandif...@linaro.org> wrote:
>> Richard Biener <richard.guent...@gmail.com> writes:
>>> 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?
>>
>> Maybe the documentation isn't clear enough, but DR_IS_CONDITIONAL
>> was supposed to mean "even if the containing statement executes
>> and runs to completion, the reference might not actually occur".
>> The example above isn't conditional in that sense because the
>> reference to b[j] does occur if the store is reached and completes.
>>
>> Masked loads and stores are conditional in that sense though.
>> The reference only occurs if the mask is nonzero; the memory
>> isn't touched otherwise. The functions are used to if-convert
>> things like:
>>
>> for (...)
>> a[i] = b[i] ? c[i] : d[i];
>>
>> where there's no guarantee that it's safe to access c[i] when !b[i]
>> (or d[i] when b[i]). No reference occurs for an all-false mask.
>
> But as you touch generic data-ref code here you should apply more
> sensible semantics to DR_IS_CONDITIONAL than just marking
> masked loads/stores but not DRs occuring inside BBs only executed
> conditionally ...
>
>>> 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?
>>
>> Dropping DR_IS_CONDITIONAL would cause us to make invalid alignment
>> assumptions in silly corner cases. I could add a scan test for it,
>> for targets with masked loads and stores. It wouldn't trigger
>> an execution failure though because we assume that targets with
>> masked loads and stores allow unaligned accesses:
>>
>> /* For now assume all conditional loads/stores support unaligned
>> access without any special code. */
>> if (is_gimple_call (stmt)
>> && gimple_call_internal_p (stmt)
>> && (gimple_call_internal_fn (stmt) == IFN_MASK_LOAD
>> || gimple_call_internal_fn (stmt) == IFN_MASK_STORE))
>> return dr_unaligned_supported;
>>
>> So the worst that would happen is that we'd supposedly peel for
>> alignment, but actually misalign everything instead, and so make
>> things slower rather than quicker.
>>
>>> 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.
>>
>> DR_MISALIGNMENT is relative to the vector alignment rather than
>> the base alignment though. So:
>
> We seem to use it that way, yes (looking at set_ptr_info_alignment
> uses). So why not fix the assert then by capping the alignment/misalignment
> we compute at this value as well? (and document this in the header
> around DR_MISALIGNMENT)
>
> Ideally we'd do alignment analysis independent of the vector size
> though (for those stupid targets with multiple vector sizes to consider...).
>
>> a) when looking for references *A1 and *A2 with the same alignment,
>> we simply have to prove that A1 % vecalign == A2 % vecalign.
>> This doesn't require any knowledge about the base alignment.
>> If we break the addresses down as:
>>
>> A1 = BASE1 + REST1, REST1 = INIT1 + OFFSET1 + X * STEP1
>> A2 = BASE2 + REST2, REST2 = INIT2 + OFFSET2 + X * STEP2
>>
>> and can prove that BASE1 == BASE2, the alignment of that base
>> isn't important. We simply need to prove that REST1 % vecalign
>> == REST2 % vecalign for all X.
>>
>> b) In the assert, we've peeled the loop so that DR_PEEL is guaranteed
>> to be vector-aligned. If DR_PEEL is A1 in the example above, we have
>> A1 % vecalign == 0, so A2 % vecalign must be 0 too. This again doesn't
>> rely on the base alignment being known.
>>
>> What a high base alignment for DR_PEEL gives us is the ability to know
>> at compile how many iterations need to be peeled to make DR_PEEL aligned.
>> But the points above apply regardless of whether we know that value at
>> compile time or not.
>>
>> In examples like the test case, we would have known at compile time that
>> VF-1 iterations would need to be peeled if we'd picked the store as the
>> DR_PEEL, but would have treated the number of peels as variable if we'd
>> picked the load. The value calculated at runtime would still have been
>> VF-1, it's just that the code wouldn't have been as efficient.
>>
>> One of the benefits of pooling the alignments for unconditional references
>> is that it no longer matters which DR we pick: the number of peels will
>> be a compile-time constant both ways.
>>
>> Thanks,
>> Richard
>>
>>> I'd rather not mix fixing this with the improvement to eventuall use a
>>> larger align for the other DR if possible.
>
> ^^^
>
> So can you fix the ICE with capping base alignment / DR_MISALIGNMENT?
Oh, and as you are touching general tree-data-refs.[ch] on my wishlist is still
"properly" computing the base alignment in tree-data-refs.[ch] itself rather
than trying to undo analyze_innermost in the vectorizer and 2nd-guessing
the alignment. Basically make alignment/misalignment first-class
citizens.
Richard.
> Richard.
>
>>> 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];
>>>> +}
