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Date: Fri, 30 Sep 2016 15:34:00 -0000
From: Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>
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To: Richard Biener <rguenther@suse.de>
CC: GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH][v4] GIMPLE store merging pass
References: <57EBE7A6.3040103@foss.arm.com> <alpine.LSU.2.11.1609291133040.26629@t29.fhfr.qr> <57EE786D.1010902@foss.arm.com>
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On 30/09/16 15:36, Kyrill Tkachov wrote:
> Hi Richard,
>
> On 29/09/16 11:45, Richard Biener wrote:
>>
>>> +
>>> +          /* In some cases get_inner_reference may return a
>>> +         MEM_REF [ptr + byteoffset].  For the purposes of this pass
>>> +         canonicalize the base_addr to MEM_REF [ptr] and take
>>> +         byteoffset into account in the bitpos.  This occurs in
>>> +         PR 23684 and this way we can catch more chains.  */
>>> +          if (TREE_CODE (base_addr) == MEM_REF
>>> +          && POINTER_TYPE_P (TREE_TYPE (TREE_OPERAND (base_addr, 0)))
>>> +          && TREE_CODE (TREE_OPERAND (base_addr, 1)) == INTEGER_CST
>> This is always an INTEGER_CST.
>>
>>> +          && tree_fits_shwi_p (TREE_OPERAND (base_addr, 1))
>> This will never allow negative offsets (but maybe this is a good thing?)
>>
>> )
>>> +        {
>>> +          bitpos += tree_to_shwi (TREE_OPERAND (base_addr, 1))
>>> +                * BITS_PER_UNIT;
>> this multiplication may overflow.  There is mem_ref_offset () which
>> you should really use here, see get_inner_reference itself (and
>> how to translate back from offset_int to HOST_WIDE_INT if it fits).
>>
>>> +
>>> +          base_addr = fold_build2 (MEM_REF, TREE_TYPE (base_addr),
>>> +                       TREE_OPERAND (base_addr, 0),
>>> +                       build_zero_cst (TREE_TYPE (
>>> +                         TREE_OPERAND (base_addr, 1))));
>> Ugh, building a tree node ... you could use TREE_OPERAND (base_addr, 0)
>> as base_addr instead?
>
> This didn't work for me because aliasing info was lost.
> So in the example:
> void
> foo2 (struct bar *p, struct bar *p2)
> {
>   p->b = 0xff;
>   p2->b = 0xa;
>   p->a = 0xfffff;
>   p2->c = 0xc;
>   p->c = 0xff;
>   p2->d = 0xbf;
>   p->d = 0xfff;
> }
>
> we end up merging p->b with p->a even though the p2->b store may alias.
> We'll record the base objects as being 'p' and 'p2' whereas with my approach
> we record them as '*p' and '*p2'. I don't suppose I could just do:
> TREE_OPERAND (base_addr, 1) = build_zero_cst (TREE_TYPE (TREE_OPERAND (base_addr, 1)));
> ?
>

Although I think I could try to make it work by using ptr_derefs_may_alias_p in the alias checks
a bit more. I'll see what I can do.

Kyrill

> Thanks,
> Kyrill
>
>>
>>> +        }
>>> +
>>> +          struct imm_store_chain_info **chain_info
>>> +        = m_stores.get (base_addr);
>>> +
>>> +          if (!invalid)
>>> +        {
>>> +          store_immediate_info *info;
>>> +          if (chain_info)
>>> +            {
>>> +              info = new store_immediate_info (
>>> +            bitsize, bitpos, rhs, lhs, stmt,
>>> +            (*chain_info)->m_store_info.length ());
>>> +              if (dump_file)
>>> +            {
>>> +              fprintf (dump_file,
>>> +                   "Recording immediate store from stmt:\n");
>>> +              print_gimple_stmt (dump_file, stmt, 0, 0);
>>> +            }
>>> +              (*chain_info)->m_store_info.safe_push (info);
>>> +              continue;
>>> +            }
>>> +
>>> +          /* Store aliases any existing chain?  */
>>> +          terminate_all_aliasing_chains (lhs, base_addr, stmt);
>>> +
>>> +          /* Start a new chain.  */
>>> +          struct imm_store_chain_info *new_chain
>>> +            = new imm_store_chain_info;
>>> +          info = new store_immediate_info (bitsize, bitpos, rhs, lhs,
>>> +                           stmt, 0);
>>> +          new_chain->m_store_info.safe_push (info);
>>> +          m_stores.put (base_addr, new_chain);
>>> +          if (dump_file)
>>> +            {
>>> +              fprintf (dump_file,
>>> +                   "Starting new chain with statement:\n");
>>> +              print_gimple_stmt (dump_file, stmt, 0, 0);
>>> +              fprintf (dump_file, "The base object is:\n");
>>> +              print_generic_expr (dump_file, base_addr, 0);
>>> +              fprintf (dump_file, "\n");
>>> +            }
>>> +        }
>>> +          else
>>> +        terminate_all_aliasing_chains (lhs, base_addr, stmt);
>>> +
>>> +          continue;
>>> +        }
>>> +
>>> +      terminate_all_aliasing_chains (NULL_TREE, NULL_TREE, stmt);
>>> +    }
>>> +      terminate_and_process_all_chains (bb);
>>> +    }
>>> +  return 0;
>>> +}
>>> +
>>> +} // anon namespace
>>> +
>>> +/* Construct and return a store merging pass object.  */
>>> +
>>> +gimple_opt_pass *
>>> +make_pass_store_merging (gcc::context *ctxt)
>>> +{
>>> +  return new pass_store_merging (ctxt);
>>> +}
>>> diff --git a/gcc/opts.c b/gcc/opts.c
>>> index 45f1f89c..e63d7e4 100644
>>> --- a/gcc/opts.c
>>> +++ b/gcc/opts.c
>>> @@ -463,6 +463,7 @@ static const struct default_options default_options_table[] =
>>>       { OPT_LEVELS_1_PLUS, OPT_ftree_dse, NULL, 1 },
>>>       { OPT_LEVELS_1_PLUS, OPT_ftree_ter, NULL, 1 },
>>>       { OPT_LEVELS_1_PLUS_NOT_DEBUG, OPT_ftree_sra, NULL, 1 },
>>> +    { OPT_LEVELS_1_PLUS_NOT_DEBUG, OPT_fstore_merging, NULL, 1 },
>> Please leave it to -O[2s]+ -- the chain invalidation is quadratic and
>> -O1 should work well even for gigantic basic blocks.
>>
>> Overall the pass looks quite well with the comments addressed.
>>
>> Thanks,
>> Richard.
>>
>>>       { OPT_LEVELS_1_PLUS, OPT_ftree_fre, NULL, 1 },
>>>       { OPT_LEVELS_1_PLUS, OPT_ftree_copy_prop, NULL, 1 },
>>>       { OPT_LEVELS_1_PLUS, OPT_ftree_sink, NULL, 1 },
>>> diff --git a/gcc/params.def b/gcc/params.def
>>> index 8907aa4..e63e594 100644
>>> --- a/gcc/params.def
>>> +++ b/gcc/params.def
>>> @@ -1100,6 +1100,12 @@ DEFPARAM (PARAM_MAX_TAIL_MERGE_COMPARISONS,
>>>             "Maximum amount of similar bbs to compare a bb with.",
>>>             10, 0, 0)
>>>   +DEFPARAM (PARAM_STORE_MERGING_ALLOW_UNALIGNED,
>>> +      "store-merging-allow-unaligned",
>>> +      "Allow the store merging pass to introduce unaligned stores "
>>> +      "if it is legal to do so",
>>> +      1, 0, 1)
>>> +
>>>   DEFPARAM (PARAM_MAX_TAIL_MERGE_ITERATIONS,
>>>             "max-tail-merge-iterations",
>>>             "Maximum amount of iterations of the pass over a function.",
>>> diff --git a/gcc/passes.def b/gcc/passes.def
>>> index 2830421..ee7dd50 100644
>>> --- a/gcc/passes.def
>>> +++ b/gcc/passes.def
>>> @@ -329,6 +329,7 @@ along with GCC; see the file COPYING3.  If not see
>>>         NEXT_PASS (pass_phiopt);
>>>         NEXT_PASS (pass_fold_builtins);
>>>         NEXT_PASS (pass_optimize_widening_mul);
>>> +      NEXT_PASS (pass_store_merging);
>>>         NEXT_PASS (pass_tail_calls);
>>>         /* If DCE is not run before checking for uninitialized uses,
>>>        we may get false warnings (e.g., testsuite/gcc.dg/uninit-5.c).
>>> diff --git a/gcc/testsuite/gcc.c-torture/execute/pr22141-1.c b/gcc/testsuite/gcc.c-torture/execute/pr22141-1.c
>>> new file mode 100644
>>> index 0000000..7c888b4
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.c-torture/execute/pr22141-1.c
>>> @@ -0,0 +1,122 @@
>>> +/* PR middle-end/22141 */
>>> +
>>> +extern void abort (void);
>>> +
>>> +struct S
>>> +{
>>> +  struct T
>>> +    {
>>> +      char a;
>>> +      char b;
>>> +      char c;
>>> +      char d;
>>> +    } t;
>>> +} u;
>>> +
>>> +struct U
>>> +{
>>> +  struct S s[4];
>>> +};
>>> +
>>> +void __attribute__((noinline))
>>> +c1 (struct T *p)
>>> +{
>>> +  if (p->a != 1 || p->b != 2 || p->c != 3 || p->d != 4)
>>> +    abort ();
>>> +  __builtin_memset (p, 0xaa, sizeof (*p));
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +c2 (struct S *p)
>>> +{
>>> +  c1 (&p->t);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +c3 (struct U *p)
>>> +{
>>> +  c2 (&p->s[2]);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f1 (void)
>>> +{
>>> +  u = (struct S) { { 1, 2, 3, 4 } };
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f2 (void)
>>> +{
>>> +  u.t.a = 1;
>>> +  u.t.b = 2;
>>> +  u.t.c = 3;
>>> +  u.t.d = 4;
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f3 (void)
>>> +{
>>> +  u.t.d = 4;
>>> +  u.t.b = 2;
>>> +  u.t.a = 1;
>>> +  u.t.c = 3;
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f4 (void)
>>> +{
>>> +  struct S v;
>>> +  v.t.a = 1;
>>> +  v.t.b = 2;
>>> +  v.t.c = 3;
>>> +  v.t.d = 4;
>>> +  c2 (&v);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f5 (struct S *p)
>>> +{
>>> +  p->t.a = 1;
>>> +  p->t.c = 3;
>>> +  p->t.d = 4;
>>> +  p->t.b = 2;
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f6 (void)
>>> +{
>>> +  struct U v;
>>> +  v.s[2].t.a = 1;
>>> +  v.s[2].t.b = 2;
>>> +  v.s[2].t.c = 3;
>>> +  v.s[2].t.d = 4;
>>> +  c3 (&v);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f7 (struct U *p)
>>> +{
>>> +  p->s[2].t.a = 1;
>>> +  p->s[2].t.c = 3;
>>> +  p->s[2].t.d = 4;
>>> +  p->s[2].t.b = 2;
>>> +}
>>> +
>>> +int
>>> +main (void)
>>> +{
>>> +  struct U w;
>>> +  f1 ();
>>> +  c2 (&u);
>>> +  f2 ();
>>> +  c1 (&u.t);
>>> +  f3 ();
>>> +  c2 (&u);
>>> +  f4 ();
>>> +  f5 (&u);
>>> +  c2 (&u);
>>> +  f6 ();
>>> +  f7 (&w);
>>> +  c3 (&w);
>>> +  return 0;
>>> +}
>>> diff --git a/gcc/testsuite/gcc.c-torture/execute/pr22141-2.c b/gcc/testsuite/gcc.c-torture/execute/pr22141-2.c
>>> new file mode 100644
>>> index 0000000..cb9cc79
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.c-torture/execute/pr22141-2.c
>>> @@ -0,0 +1,122 @@
>>> +/* PR middle-end/22141 */
>>> +
>>> +extern void abort (void);
>>> +
>>> +struct S
>>> +{
>>> +  struct T
>>> +    {
>>> +      char a;
>>> +      char b;
>>> +      char c;
>>> +      char d;
>>> +    } t;
>>> +} u __attribute__((aligned));
>>> +
>>> +struct U
>>> +{
>>> +  struct S s[4];
>>> +};
>>> +
>>> +void __attribute__((noinline))
>>> +c1 (struct T *p)
>>> +{
>>> +  if (p->a != 1 || p->b != 2 || p->c != 3 || p->d != 4)
>>> +    abort ();
>>> +  __builtin_memset (p, 0xaa, sizeof (*p));
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +c2 (struct S *p)
>>> +{
>>> +  c1 (&p->t);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +c3 (struct U *p)
>>> +{
>>> +  c2 (&p->s[2]);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f1 (void)
>>> +{
>>> +  u = (struct S) { { 1, 2, 3, 4 } };
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f2 (void)
>>> +{
>>> +  u.t.a = 1;
>>> +  u.t.b = 2;
>>> +  u.t.c = 3;
>>> +  u.t.d = 4;
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f3 (void)
>>> +{
>>> +  u.t.d = 4;
>>> +  u.t.b = 2;
>>> +  u.t.a = 1;
>>> +  u.t.c = 3;
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f4 (void)
>>> +{
>>> +  struct S v __attribute__((aligned));
>>> +  v.t.a = 1;
>>> +  v.t.b = 2;
>>> +  v.t.c = 3;
>>> +  v.t.d = 4;
>>> +  c2 (&v);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f5 (struct S *p)
>>> +{
>>> +  p->t.a = 1;
>>> +  p->t.c = 3;
>>> +  p->t.d = 4;
>>> +  p->t.b = 2;
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f6 (void)
>>> +{
>>> +  struct U v __attribute__((aligned));
>>> +  v.s[2].t.a = 1;
>>> +  v.s[2].t.b = 2;
>>> +  v.s[2].t.c = 3;
>>> +  v.s[2].t.d = 4;
>>> +  c3 (&v);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f7 (struct U *p)
>>> +{
>>> +  p->s[2].t.a = 1;
>>> +  p->s[2].t.c = 3;
>>> +  p->s[2].t.d = 4;
>>> +  p->s[2].t.b = 2;
>>> +}
>>> +
>>> +int
>>> +main (void)
>>> +{
>>> +  struct U w __attribute__((aligned));
>>> +  f1 ();
>>> +  c2 (&u);
>>> +  f2 ();
>>> +  c1 (&u.t);
>>> +  f3 ();
>>> +  c2 (&u);
>>> +  f4 ();
>>> +  f5 (&u);
>>> +  c2 (&u);
>>> +  f6 ();
>>> +  f7 (&w);
>>> +  c3 (&w);
>>> +  return 0;
>>> +}
>>> diff --git a/gcc/testsuite/gcc.dg/store_merging_1.c b/gcc/testsuite/gcc.dg/store_merging_1.c
>>> new file mode 100644
>>> index 0000000..09a4d14
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/store_merging_1.c
>>> @@ -0,0 +1,35 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-require-effective-target non_strict_align } */
>>> +/* { dg-options "-O -fdump-tree-store-merging" } */
>>> +
>>> +struct bar {
>>> +  int a;
>>> +  char b;
>>> +  char c;
>>> +  char d;
>>> +  char e;
>>> +  char f;
>>> +  char g;
>>> +};
>>> +
>>> +void
>>> +foo1 (struct bar *p)
>>> +{
>>> +  p->b = 0;
>>> +  p->a = 0;
>>> +  p->c = 0;
>>> +  p->d = 0;
>>> +  p->e = 0;
>>> +}
>>> +
>>> +void
>>> +foo2 (struct bar *p)
>>> +{
>>> +  p->b = 0;
>>> +  p->a = 0;
>>> +  p->c = 1;
>>> +  p->d = 0;
>>> +  p->e = 0;
>>> +}
>>> +
>>> +/* { dg-final { scan-tree-dump-times "Merging successful" 2 "store-merging" } } */
>>> diff --git a/gcc/testsuite/gcc.dg/store_merging_2.c b/gcc/testsuite/gcc.dg/store_merging_2.c
>>> new file mode 100644
>>> index 0000000..d3acc2d
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/store_merging_2.c
>>> @@ -0,0 +1,80 @@
>>> +/* { dg-do run } */
>>> +/* { dg-require-effective-target non_strict_align } */
>>> +/* { dg-options "-O -fdump-tree-store-merging" } */
>>> +
>>> +struct bar
>>> +{
>>> +  int a;
>>> +  unsigned char b;
>>> +  unsigned char c;
>>> +  short d;
>>> +  unsigned char e;
>>> +  unsigned char f;
>>> +  unsigned char g;
>>> +};
>>> +
>>> +__attribute__ ((noinline)) void
>>> +foozero (struct bar *p)
>>> +{
>>> +  p->b = 0;
>>> +  p->a = 0;
>>> +  p->c = 0;
>>> +  p->d = 0;
>>> +  p->e = 0;
>>> +  p->f = 0;
>>> +  p->g = 0;
>>> +}
>>> +
>>> +__attribute__ ((noinline)) void
>>> +foo1 (struct bar *p)
>>> +{
>>> +  p->b = 1;
>>> +  p->a = 2;
>>> +  p->c = 3;
>>> +  p->d = 4;
>>> +  p->e = 5;
>>> +  p->f = 0;
>>> +  p->g = 0xff;
>>> +}
>>> +
>>> +__attribute__ ((noinline)) void
>>> +foo2 (struct bar *p, struct bar *p2)
>>> +{
>>> +  p->b = 0xff;
>>> +  p2->b = 0xa;
>>> +  p->a = 0xfffff;
>>> +  p2->c = 0xc;
>>> +  p->c = 0xff;
>>> +  p2->d = 0xbf;
>>> +  p->d = 0xfff;
>>> +}
>>> +
>>> +int
>>> +main (void)
>>> +{
>>> +  struct bar b1, b2;
>>> +  foozero (&b1);
>>> +  foozero (&b2);
>>> +
>>> +  foo1 (&b1);
>>> +  if (b1.b != 1 || b1.a != 2 || b1.c != 3 || b1.d != 4 || b1.e != 5
>>> +      || b1.f != 0 || b1.g != 0xff)
>>> +    __builtin_abort ();
>>> +
>>> +  foozero (&b1);
>>> +  /* Make sure writes to aliasing struct pointers preserve the
>>> +     correct order.  */
>>> +  foo2 (&b1, &b1);
>>> +  if (b1.b != 0xa || b1.a != 0xfffff || b1.c != 0xff || b1.d != 0xfff)
>>> +    __builtin_abort ();
>>> +
>>> +  foozero (&b1);
>>> +  foo2 (&b1, &b2);
>>> +  if (b1.a != 0xfffff || b1.b != 0xff || b1.c != 0xff || b1.d != 0xfff
>>> +      || b2.b != 0xa || b2.c != 0xc || b2.d != 0xbf)
>>> +    __builtin_abort ();
>>> +
>>> +  return 0;
>>> +}
>>> +
>>> +/* { dg-final { scan-tree-dump-times "Merging successful" 2 "store-merging" } } */
>>> diff --git a/gcc/testsuite/gcc.dg/store_merging_3.c b/gcc/testsuite/gcc.dg/store_merging_3.c
>>> new file mode 100644
>>> index 0000000..cd756c1
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/store_merging_3.c
>>> @@ -0,0 +1,32 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-require-effective-target non_strict_align } */
>>> +/* { dg-options "-O -fdump-tree-store-merging" } */
>>> +
>>> +/* Make sure stores to volatile addresses don't get combined with
>>> +   other accesses.  */
>>> +
>>> +struct bar
>>> +{
>>> +  int a;
>>> +  char b;
>>> +  char c;
>>> +  volatile short d;
>>> +  char e;
>>> +  char f;
>>> +  char g;
>>> +};
>>> +
>>> +void
>>> +foozero (struct bar *p)
>>> +{
>>> +  p->b = 0xa;
>>> +  p->a = 0xb;
>>> +  p->c = 0xc;
>>> +  p->d = 0;
>>> +  p->e = 0xd;
>>> +  p->f = 0xe;
>>> +  p->g = 0xf;
>>> +}
>>> +
>>> +/* { dg-final { scan-tree-dump "Volatile access terminates all chains" "store-merging" } } */
>>> +/* { dg-final { scan-tree-dump-times "=\{v\} 0;" 1 "store-merging" } } */
>>> diff --git a/gcc/testsuite/gcc.dg/store_merging_4.c b/gcc/testsuite/gcc.dg/store_merging_4.c
>>> new file mode 100644
>>> index 0000000..4bf9025
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/store_merging_4.c
>>> @@ -0,0 +1,32 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-require-effective-target non_strict_align } */
>>> +/* { dg-options "-O -fdump-tree-store-merging" } */
>>> +
>>> +/* Check that we can merge interleaving stores that are guaranteed
>>> +   to be non-aliasing.  */
>>> +
>>> +struct bar
>>> +{
>>> +  int a;
>>> +  char b;
>>> +  char c;
>>> +  short d;
>>> +  char e;
>>> +  char f;
>>> +  char g;
>>> +};
>>> +
>>> +void
>>> +foozero (struct bar *restrict p, struct bar *restrict p2)
>>> +{
>>> +  p->b = 0xff;
>>> +  p2->b = 0xa;
>>> +  p->a = 0xfffff;
>>> +  p2->a = 0xab;
>>> +  p2->c = 0xc;
>>> +  p->c = 0xff;
>>> +  p2->d = 0xbf;
>>> +  p->d = 0xfff;
>>> +}
>>> +
>>> +/* { dg-final { scan-tree-dump-times "Merging successful" 2 "store-merging" } } */
>>> diff --git a/gcc/testsuite/gcc.dg/store_merging_5.c b/gcc/testsuite/gcc.dg/store_merging_5.c
>>> new file mode 100644
>>> index 0000000..3b82420
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/store_merging_5.c
>>> @@ -0,0 +1,30 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-require-effective-target non_strict_align } */
>>> +/* { dg-options "-O -fdump-tree-store-merging" } */
>>> +
>>> +/* Make sure that non-aliasing non-constant interspersed stores do not
>>> +   stop chains.  */
>>> +
>>> +struct bar {
>>> +  int a;
>>> +  char b;
>>> +  char c;
>>> +  char d;
>>> +  char e;
>>> +  char g;
>>> +};
>>> +
>>> +void
>>> +foo1 (struct bar *p, char tmp)
>>> +{
>>> +  p->a = 0;
>>> +  p->b = 0;
>>> +  p->g = tmp;
>>> +  p->c = 0;
>>> +  p->d = 0;
>>> +  p->e = 0;
>>> +}
>>> +
>>> +
>>> +/* { dg-final { scan-tree-dump-times "Merging successful" 1 "store-merging" } } */
>>> +/* { dg-final { scan-tree-dump-times "MEM\\\[.*\\\]" 1 "store-merging" } } */
>>> diff --git a/gcc/testsuite/gcc.dg/store_merging_6.c b/gcc/testsuite/gcc.dg/store_merging_6.c
>>> new file mode 100644
>>> index 0000000..7d89baf
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/store_merging_6.c
>>> @@ -0,0 +1,53 @@
>>> +/* { dg-do run } */
>>> +/* { dg-require-effective-target non_strict_align } */
>>> +/* { dg-options "-O -fdump-tree-store-merging" } */
>>> +
>>> +/* Check that we can widen accesses to bitfields.  */
>>> +
>>> +struct bar {
>>> +  int a : 3;
>>> +  unsigned char b : 4;
>>> +  unsigned char c : 1;
>>> +  char d;
>>> +  char e;
>>> +  char f;
>>> +  char g;
>>> +};
>>> +
>>> +__attribute__ ((noinline)) void
>>> +foozero (struct bar *p)
>>> +{
>>> +  p->b = 0;
>>> +  p->a = 0;
>>> +  p->c = 0;
>>> +  p->d = 0;
>>> +  p->e = 0;
>>> +  p->f = 0;
>>> +  p->g = 0;
>>> +}
>>> +
>>> +__attribute__ ((noinline)) void
>>> +foo1 (struct bar *p)
>>> +{
>>> +  p->b = 3;
>>> +  p->a = 2;
>>> +  p->c = 1;
>>> +  p->d = 4;
>>> +  p->e = 5;
>>> +}
>>> +
>>> +int
>>> +main (void)
>>> +{
>>> +  struct bar p;
>>> +  foozero (&p);
>>> +  foo1 (&p);
>>> +  if (p.a != 2 || p.b != 3 || p.c != 1 || p.d != 4 || p.e != 5
>>> +      || p.f != 0 || p.g != 0)
>>> +    __builtin_abort ();
>>> +
>>> +  return 0;
>>> +}
>>> +
>>> +
>>> +/* { dg-final { scan-tree-dump-times "Merging successful" 2 "store-merging" } } */
>>> diff --git a/gcc/testsuite/gcc.dg/store_merging_7.c b/gcc/testsuite/gcc.dg/store_merging_7.c
>>> new file mode 100644
>>> index 0000000..02008f7
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/store_merging_7.c
>>> @@ -0,0 +1,26 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-require-effective-target non_strict_align } */
>>> +/* { dg-options "-O -fdump-tree-store-merging" } */
>>> +
>>> +/* Check that we can merge consecutive array members through the pointer.
>>> +   PR rtl-optimization/23684.  */
>>> +
>>> +void
>>> +foo (char *input)
>>> +{
>>> +  input = __builtin_assume_aligned (input, 8);
>>> +  input[0] = 'H';
>>> +  input[1] = 'e';
>>> +  input[2] = 'l';
>>> +  input[3] = 'l';
>>> +  input[4] = 'o';
>>> +  input[5] = ' ';
>>> +  input[6] = 'w';
>>> +  input[7] = 'o';
>>> +  input[8] = 'r';
>>> +  input[9] = 'l';
>>> +  input[10] = 'd';
>>> +  input[11] = '\0';
>>> +}
>>> +
>>> +/* { dg-final { scan-tree-dump-times "Merging successful" 1 "store-merging" } } */
>>> diff --git a/gcc/testsuite/gcc.target/aarch64/ldp_stp_1.c b/gcc/testsuite/gcc.target/aarch64/ldp_stp_1.c
>>> index f02e55f..9de4e77 100644
>>> --- a/gcc/testsuite/gcc.target/aarch64/ldp_stp_1.c
>>> +++ b/gcc/testsuite/gcc.target/aarch64/ldp_stp_1.c
>>> @@ -3,22 +3,22 @@
>>>   int arr[4][4];
>>>     void
>>> -foo ()
>>> +foo (int x, int y)
>>>   {
>>> -  arr[0][1] = 1;
>>> -  arr[1][0] = -1;
>>> -  arr[2][0] = 1;
>>> -  arr[1][1] = -1;
>>> -  arr[0][2] = 1;
>>> -  arr[0][3] = -1;
>>> -  arr[1][2] = 1;
>>> -  arr[2][1] = -1;
>>> -  arr[3][0] = 1;
>>> -  arr[3][1] = -1;
>>> -  arr[2][2] = 1;
>>> -  arr[1][3] = -1;
>>> -  arr[2][3] = 1;
>>> -  arr[3][2] = -1;
>>> +  arr[0][1] = x;
>>> +  arr[1][0] = y;
>>> +  arr[2][0] = x;
>>> +  arr[1][1] = y;
>>> +  arr[0][2] = x;
>>> +  arr[0][3] = y;
>>> +  arr[1][2] = x;
>>> +  arr[2][1] = y;
>>> +  arr[3][0] = x;
>>> +  arr[3][1] = y;
>>> +  arr[2][2] = x;
>>> +  arr[1][3] = y;
>>> +  arr[2][3] = x;
>>> +  arr[3][2] = y;
>>>   }
>>>     /* { dg-final { scan-assembler-times "stp\tw\[0-9\]+, w\[0-9\]" 7 } } */
>>> diff --git a/gcc/testsuite/gcc.target/aarch64/ldp_stp_4.c b/gcc/testsuite/gcc.target/aarch64/ldp_stp_4.c
>>> index 40056b1..824f0d2 100644
>>> --- a/gcc/testsuite/gcc.target/aarch64/ldp_stp_4.c
>>> +++ b/gcc/testsuite/gcc.target/aarch64/ldp_stp_4.c
>>> @@ -3,22 +3,22 @@
>>>   float arr[4][4];
>>>     void
>>> -foo ()
>>> +foo (float x, float y)
>>>   {
>>> -  arr[0][1] = 1;
>>> -  arr[1][0] = -1;
>>> -  arr[2][0] = 1;
>>> -  arr[1][1] = -1;
>>> -  arr[0][2] = 1;
>>> -  arr[0][3] = -1;
>>> -  arr[1][2] = 1;
>>> -  arr[2][1] = -1;
>>> -  arr[3][0] = 1;
>>> -  arr[3][1] = -1;
>>> -  arr[2][2] = 1;
>>> -  arr[1][3] = -1;
>>> -  arr[2][3] = 1;
>>> -  arr[3][2] = -1;
>>> +  arr[0][1] = x;
>>> +  arr[1][0] = y;
>>> +  arr[2][0] = x;
>>> +  arr[1][1] = y;
>>> +  arr[0][2] = x;
>>> +  arr[0][3] = y;
>>> +  arr[1][2] = x;
>>> +  arr[2][1] = y;
>>> +  arr[3][0] = x;
>>> +  arr[3][1] = y;
>>> +  arr[2][2] = x;
>>> +  arr[1][3] = y;
>>> +  arr[2][3] = x;
>>> +  arr[3][2] = y;
>>>   }
>>>     /* { dg-final { scan-assembler-times "stp\ts\[0-9\]+, s\[0-9\]" 7 } } */
>>> diff --git a/gcc/testsuite/gcc.target/i386/pr22141.c b/gcc/testsuite/gcc.target/i386/pr22141.c
>>> new file mode 100644
>>> index 0000000..036422e
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.target/i386/pr22141.c
>>> @@ -0,0 +1,126 @@
>>> +/* PR middle-end/22141 */
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-Os" } */
>>> +
>>> +extern void abort (void);
>>> +
>>> +struct S
>>> +{
>>> +  struct T
>>> +    {
>>> +      char a;
>>> +      char b;
>>> +      char c;
>>> +      char d;
>>> +    } t;
>>> +} u;
>>> +
>>> +struct U
>>> +{
>>> +  struct S s[4];
>>> +};
>>> +
>>> +void __attribute__((noinline))
>>> +c1 (struct T *p)
>>> +{
>>> +  if (p->a != 1 || p->b != 2 || p->c != 3 || p->d != 4)
>>> +    abort ();
>>> +  __builtin_memset (p, 0xaa, sizeof (*p));
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +c2 (struct S *p)
>>> +{
>>> +  c1 (&p->t);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +c3 (struct U *p)
>>> +{
>>> +  c2 (&p->s[2]);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f1 (void)
>>> +{
>>> +  u = (struct S) { { 1, 2, 3, 4 } };
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f2 (void)
>>> +{
>>> +  u.t.a = 1;
>>> +  u.t.b = 2;
>>> +  u.t.c = 3;
>>> +  u.t.d = 4;
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f3 (void)
>>> +{
>>> +  u.t.d = 4;
>>> +  u.t.b = 2;
>>> +  u.t.a = 1;
>>> +  u.t.c = 3;
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f4 (void)
>>> +{
>>> +  struct S v;
>>> +  v.t.a = 1;
>>> +  v.t.b = 2;
>>> +  v.t.c = 3;
>>> +  v.t.d = 4;
>>> +  c2 (&v);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f5 (struct S *p)
>>> +{
>>> +  p->t.a = 1;
>>> +  p->t.c = 3;
>>> +  p->t.d = 4;
>>> +  p->t.b = 2;
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f6 (void)
>>> +{
>>> +  struct U v;
>>> +  v.s[2].t.a = 1;
>>> +  v.s[2].t.b = 2;
>>> +  v.s[2].t.c = 3;
>>> +  v.s[2].t.d = 4;
>>> +  c3 (&v);
>>> +}
>>> +
>>> +void __attribute__((noinline))
>>> +f7 (struct U *p)
>>> +{
>>> +  p->s[2].t.a = 1;
>>> +  p->s[2].t.c = 3;
>>> +  p->s[2].t.d = 4;
>>> +  p->s[2].t.b = 2;
>>> +}
>>> +
>>> +int
>>> +main (void)
>>> +{
>>> +  struct U w;
>>> +  f1 ();
>>> +  c2 (&u);
>>> +  f2 ();
>>> +  c1 (&u.t);
>>> +  f3 ();
>>> +  c2 (&u);
>>> +  f4 ();
>>> +  f5 (&u);
>>> +  c2 (&u);
>>> +  f6 ();
>>> +  f7 (&w);
>>> +  c3 (&w);
>>> +  return 0;
>>> +}
>>> +
>>> +/* { dg-final { scan-assembler-times "67305985\|4030201" 7 } } */
>>> diff --git a/gcc/testsuite/gcc.target/i386/pr34012.c b/gcc/testsuite/gcc.target/i386/pr34012.c
>>> index 00b1240..d0cffa0 100644
>>> --- a/gcc/testsuite/gcc.target/i386/pr34012.c
>>> +++ b/gcc/testsuite/gcc.target/i386/pr34012.c
>>> @@ -1,7 +1,7 @@
>>>   /* PR rtl-optimization/34012 */
>>>   /* { dg-do compile } */
>>>   /* { dg-require-effective-target lp64 } */
>>> -/* { dg-options "-O2" } */
>>> +/* { dg-options "-O2 -fno-store-merging" } */
>>>     void bar (long int *);
>>>   void
>>> diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
>>> index a706729..b5373a3 100644
>>> --- a/gcc/tree-pass.h
>>> +++ b/gcc/tree-pass.h
>>> @@ -425,6 +425,7 @@ extern gimple_opt_pass *make_pass_late_warn_uninitialized (gcc::context *ctxt);
>>>   extern gimple_opt_pass *make_pass_cse_reciprocals (gcc::context *ctxt);
>>>   extern gimple_opt_pass *make_pass_cse_sincos (gcc::context *ctxt);
>>>   extern gimple_opt_pass *make_pass_optimize_bswap (gcc::context *ctxt);
>>> +extern gimple_opt_pass *make_pass_store_merging (gcc::context *ctxt);
>>>   extern gimple_opt_pass *make_pass_optimize_widening_mul (gcc::context *ctxt);
>>>   extern gimple_opt_pass *make_pass_warn_function_return (gcc::context *ctxt);
>>>   extern gimple_opt_pass *make_pass_warn_function_noreturn (gcc::context *ctxt);
>