[V2/PATCH] Fix tree-optimization/102216: missed optimization causing Warray-bounds

  From: Andrew Pinski <apinski@marvell.com>

The problem here is tree-ssa-forwprop.c likes to produce
&MEM <const char *> [(void *)_4 + 152B] which is the same as
_4 p+ 152 which the rest of GCC likes better.
This implements this transformation back to pointer plus to
improve better code generation later on.

OK? Bootstrapped and tested on aarch64-linux-gnu.

Changes from v1:
* v2: Add comments.

gcc/ChangeLog:

	PR tree-optimization/102216
	* tree-ssa-forwprop.c (rewrite_assign_addr): New function.
	(forward_propagate_addr_expr_1): Use rewrite_assign_addr
	when rewriting into the addr_expr into an assignment.

gcc/testsuite/ChangeLog:

	PR tree-optimization/102216
	* g++.dg/tree-ssa/pr102216.C: New test.
---
 gcc/testsuite/g++.dg/tree-ssa/pr102216.C | 22 +++++++++
 gcc/tree-ssa-forwprop.c                  | 58 ++++++++++++++++++------
 2 files changed, 67 insertions(+), 13 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr102216.C
  

On 27 October 2021 11:59:58 CEST, apinski--- via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>From: Andrew Pinski <apinski@marvell.com>
>
>The problem here is tree-ssa-forwprop.c likes to produce
>&MEM <const char *> [(void *)_4 + 152B] which is the same as
>_4 p+ 152 which the rest of GCC likes better.
>This implements this transformation back to pointer plus to
>improve better code generation later on.
>
>OK? Bootstrapped and tested on aarch64-linux-gnu.
>
>Changes from v1:
>* v2: Add comments.
>
>gcc/ChangeLog:
>
>	PR tree-optimization/102216
>	* tree-ssa-forwprop.c (rewrite_assign_addr): New function.
>	(forward_propagate_addr_expr_1): Use rewrite_assign_addr
>	when rewriting into the addr_expr into an assignment.
>
>gcc/testsuite/ChangeLog:
>
>	PR tree-optimization/102216
>	* g++.dg/tree-ssa/pr102216.C: New test.
>---
> gcc/testsuite/g++.dg/tree-ssa/pr102216.C | 22 +++++++++
> gcc/tree-ssa-forwprop.c                  | 58 ++++++++++++++++++------
> 2 files changed, 67 insertions(+), 13 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr102216.C
>
>diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
>new file mode 100644
>index 00000000000..b903e4eb57d
>--- /dev/null
>+++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
>@@ -0,0 +1,22 @@
>+/* { dg-options "-O2 -fdump-tree-optimized" } */
>+void link_error ();
>+void g ()
>+{
>+  const char **language_names;
>+
>+  language_names = new const char *[6];
>+
>+  const char **language_names_p = language_names;
>+
>+  language_names_p++;
>+  language_names_p++;
>+  language_names_p++;
>+
>+  if ( (language_names_p) - (language_names+3) != 0)
>+    link_error();
>+  delete[] language_names;
>+}
>+/* We should have removed the link_error on the gimple level as GCC should
>+   be able to tell that language_names_p is the same as language_names+3.  */
>+/* { dg-final { scan-tree-dump-times "link_error" 0 "optimized" } } */
>+
>diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
>index a830bab78ba..e4331c60525 100644
>--- a/gcc/tree-ssa-forwprop.c
>+++ b/gcc/tree-ssa-forwprop.c
>@@ -637,6 +637,47 @@ forward_propagate_into_cond (gimple_stmt_iterator *gsi_p)
>   return 0;
> }
> 
>+/* Rewrite the DEF_RHS as needed into the (plain) use statement.  */
>+
>+static void
>+rewrite_assign_addr (gimple_stmt_iterator *use_stmt_gsi, tree def_rhs)
>+{
>+  tree def_rhs_base;
>+  poly_int64 def_rhs_offset;
>+
>+  /* Get the base and offset.  */
>+  if ((def_rhs_base = get_addr_base_and_unit_offset (TREE_OPERAND (def_rhs, 0),
>+						     &def_rhs_offset)))
>+    {
>+      tree new_ptr;
>+      poly_offset_int off = 0;
>+
>+      /* If the base was a MEM, then add the offset to the other
>+         offset and adjust the base. */
>+      if (TREE_CODE (def_rhs_base) == MEM_REF)
>+	{
>+	  off += mem_ref_offset (def_rhs_base);
>+	  new_ptr = TREE_OPERAND (def_rhs_base, 0);
>+	}
>+      else
>+	new_ptr = build_fold_addr_expr (def_rhs_base);
>+
>+      /* If we have the new base is not an address express, then use a p+ expression
>+         as the new expression instead of &MEM[x, offset]. */
>+      if (TREE_CODE (new_ptr) != ADDR_EXPR)
>+	{
>+	  tree offset = wide_int_to_tree (sizetype, off);
>+	  def_rhs = build2 (POINTER_PLUS_EXPR, TREE_TYPE (def_rhs), new_ptr, offset);
>+	}
>+    }
>+
>+  /* Replace the rhs with the new expression.  */
>+  def_rhs = unshare_expr (def_rhs);
>+  gimple_assign_set_rhs_from_tree (use_stmt_gsi, def_rhs);
>+  gimple *use_stmt = gsi_stmt (*use_stmt_gsi);
>+  update_stmt (use_stmt);
>+}
>+
> /* We've just substituted an ADDR_EXPR into stmt.  Update all the
>    relevant data structures to match.  */
> 
>@@ -696,8 +737,8 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
>       if (single_use_p
> 	  && useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE (def_rhs)))
> 	{
>-	  gimple_assign_set_rhs1 (use_stmt, unshare_expr (def_rhs));
>-	  gimple_assign_set_rhs_code (use_stmt, TREE_CODE (def_rhs));
>+	  rewrite_assign_addr (use_stmt_gsi, def_rhs);
>+	  gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
> 	  return true;
> 	}
> 
>@@ -741,14 +782,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
>       if (forward_propagate_addr_expr (lhs, new_def_rhs, single_use_p))
> 	return true;
> 
>-      if (useless_type_conversion_p (TREE_TYPE (lhs),
>-				     TREE_TYPE (new_def_rhs)))
>-	gimple_assign_set_rhs_with_ops (use_stmt_gsi, TREE_CODE (new_def_rhs),
>-					new_def_rhs);
>-      else if (is_gimple_min_invariant (new_def_rhs))
>-	gimple_assign_set_rhs_with_ops (use_stmt_gsi, NOP_EXPR, new_def_rhs);
>-      else
>-	return false;
>+      rewrite_assign_addr (use_stmt_gsi, new_def_rhs);
>       gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
>       update_stmt (use_stmt);

ISTM the above update_stmt is redundant now?
thanks,

>       return true;
>@@ -951,9 +985,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> 					      unshare_expr (def_rhs),
> 					      fold_convert (ptr_type_node,
> 							    rhs2)));
>-      gimple_assign_set_rhs_from_tree (use_stmt_gsi, new_rhs);
>-      use_stmt = gsi_stmt (*use_stmt_gsi);
>-      update_stmt (use_stmt);
>+      rewrite_assign_addr (use_stmt_gsi, new_rhs);
>       tidy_after_forward_propagate_addr (use_stmt);
>       return true;
>     }
  

On Wed, Oct 27, 2021 at 12:00 PM apinski--- via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> From: Andrew Pinski <apinski@marvell.com>
>
> The problem here is tree-ssa-forwprop.c likes to produce
> &MEM <const char *> [(void *)_4 + 152B] which is the same as
> _4 p+ 152 which the rest of GCC likes better.
> This implements this transformation back to pointer plus to
> improve better code generation later on.

Why do you think so?  Can you pin-point the transform that now
fixes the new testcase?

Comments below

> OK? Bootstrapped and tested on aarch64-linux-gnu.
>
> Changes from v1:
> * v2: Add comments.
>
> gcc/ChangeLog:
>
>         PR tree-optimization/102216
>         * tree-ssa-forwprop.c (rewrite_assign_addr): New function.
>         (forward_propagate_addr_expr_1): Use rewrite_assign_addr
>         when rewriting into the addr_expr into an assignment.
>
> gcc/testsuite/ChangeLog:
>
>         PR tree-optimization/102216
>         * g++.dg/tree-ssa/pr102216.C: New test.
> ---
>  gcc/testsuite/g++.dg/tree-ssa/pr102216.C | 22 +++++++++
>  gcc/tree-ssa-forwprop.c                  | 58 ++++++++++++++++++------
>  2 files changed, 67 insertions(+), 13 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr102216.C
>
> diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> new file mode 100644
> index 00000000000..b903e4eb57d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> @@ -0,0 +1,22 @@
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +void link_error ();
> +void g ()
> +{
> +  const char **language_names;
> +
> +  language_names = new const char *[6];
> +
> +  const char **language_names_p = language_names;
> +
> +  language_names_p++;
> +  language_names_p++;
> +  language_names_p++;
> +
> +  if ( (language_names_p) - (language_names+3) != 0)
> +    link_error();
> +  delete[] language_names;
> +}
> +/* We should have removed the link_error on the gimple level as GCC should
> +   be able to tell that language_names_p is the same as language_names+3.  */
> +/* { dg-final { scan-tree-dump-times "link_error" 0 "optimized" } } */
> +
> diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
> index a830bab78ba..e4331c60525 100644
> --- a/gcc/tree-ssa-forwprop.c
> +++ b/gcc/tree-ssa-forwprop.c
> @@ -637,6 +637,47 @@ forward_propagate_into_cond (gimple_stmt_iterator *gsi_p)
>    return 0;
>  }
>
> +/* Rewrite the DEF_RHS as needed into the (plain) use statement.  */
> +
> +static void
> +rewrite_assign_addr (gimple_stmt_iterator *use_stmt_gsi, tree def_rhs)
> +{
> +  tree def_rhs_base;
> +  poly_int64 def_rhs_offset;
> +
> +  /* Get the base and offset.  */
> +  if ((def_rhs_base = get_addr_base_and_unit_offset (TREE_OPERAND (def_rhs, 0),
> +                                                    &def_rhs_offset)))

So this will cause us to rewrite &MEM[p_1].a.b.c; to a pointer-plus,
right?  Don't
we want to preserve that for object-size stuff?  So maybe directly pattern
match ADDR_EXPR <MEM_REF <SSA_NAME, ..>> only?

> +    {
> +      tree new_ptr;
> +      poly_offset_int off = 0;
> +
> +      /* If the base was a MEM, then add the offset to the other
> +         offset and adjust the base. */
> +      if (TREE_CODE (def_rhs_base) == MEM_REF)
> +       {
> +         off += mem_ref_offset (def_rhs_base);
> +         new_ptr = TREE_OPERAND (def_rhs_base, 0);
> +       }
> +      else
> +       new_ptr = build_fold_addr_expr (def_rhs_base);
> +
> +      /* If we have the new base is not an address express, then use a p+ expression
> +         as the new expression instead of &MEM[x, offset]. */
> +      if (TREE_CODE (new_ptr) != ADDR_EXPR)
> +       {
> +         tree offset = wide_int_to_tree (sizetype, off);
> +         def_rhs = build2 (POINTER_PLUS_EXPR, TREE_TYPE (def_rhs), new_ptr, offset);

Ick.  You should be able to use gimple_assign_set_rhs_with_ops.

> +       }
> +    }
> +
> +  /* Replace the rhs with the new expression.  */
> +  def_rhs = unshare_expr (def_rhs);

and definitely no need to unshare anything here?

> +  gimple_assign_set_rhs_from_tree (use_stmt_gsi, def_rhs);
> +  gimple *use_stmt = gsi_stmt (*use_stmt_gsi);
> +  update_stmt (use_stmt);
> +}
> +
>  /* We've just substituted an ADDR_EXPR into stmt.  Update all the
>     relevant data structures to match.  */
>
> @@ -696,8 +737,8 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
>        if (single_use_p
>           && useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE (def_rhs)))
>         {
> -         gimple_assign_set_rhs1 (use_stmt, unshare_expr (def_rhs));
> -         gimple_assign_set_rhs_code (use_stmt, TREE_CODE (def_rhs));
> +         rewrite_assign_addr (use_stmt_gsi, def_rhs);
> +         gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
>           return true;
>         }
>
> @@ -741,14 +782,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
>        if (forward_propagate_addr_expr (lhs, new_def_rhs, single_use_p))
>         return true;
>
> -      if (useless_type_conversion_p (TREE_TYPE (lhs),
> -                                    TREE_TYPE (new_def_rhs)))
> -       gimple_assign_set_rhs_with_ops (use_stmt_gsi, TREE_CODE (new_def_rhs),
> -                                       new_def_rhs);
> -      else if (is_gimple_min_invariant (new_def_rhs))
> -       gimple_assign_set_rhs_with_ops (use_stmt_gsi, NOP_EXPR, new_def_rhs);
> -      else
> -       return false;
> +      rewrite_assign_addr (use_stmt_gsi, new_def_rhs);
>        gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
>        update_stmt (use_stmt);
>        return true;
> @@ -951,9 +985,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
>                                               unshare_expr (def_rhs),
>                                               fold_convert (ptr_type_node,
>                                                             rhs2)));
> -      gimple_assign_set_rhs_from_tree (use_stmt_gsi, new_rhs);
> -      use_stmt = gsi_stmt (*use_stmt_gsi);
> -      update_stmt (use_stmt);
> +      rewrite_assign_addr (use_stmt_gsi, new_rhs);

so you only do this after addr_expr forwarding but not on stmts in
general?  You could
do it that way in the 2nd loop over the BB.

>        tidy_after_forward_propagate_addr (use_stmt);
>        return true;
>      }
> --
> 2.17.1
>
  

On 10/27/21 3:59 AM, apinski--- via Gcc-patches wrote:
> From: Andrew Pinski <apinski@marvell.com>
> 
> The problem here is tree-ssa-forwprop.c likes to produce
> &MEM <const char *> [(void *)_4 + 152B] which is the same as
> _4 p+ 152 which the rest of GCC likes better.
> This implements this transformation back to pointer plus to
> improve better code generation later on.

Since the purpose of this transformation is to avoid a bogus
-Warray-bounds can you please include a test case showing
the difference it makes? (I.e., one that warns without
the patch and doesn't with it.  The test in the patch doesn't
trigger a warning for me.)

Thanks
Martin

> 
> OK? Bootstrapped and tested on aarch64-linux-gnu.
> 
> Changes from v1:
> * v2: Add comments.
> 
> gcc/ChangeLog:
> 
> 	PR tree-optimization/102216
> 	* tree-ssa-forwprop.c (rewrite_assign_addr): New function.
> 	(forward_propagate_addr_expr_1): Use rewrite_assign_addr
> 	when rewriting into the addr_expr into an assignment.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR tree-optimization/102216
> 	* g++.dg/tree-ssa/pr102216.C: New test.
> ---
>   gcc/testsuite/g++.dg/tree-ssa/pr102216.C | 22 +++++++++
>   gcc/tree-ssa-forwprop.c                  | 58 ++++++++++++++++++------
>   2 files changed, 67 insertions(+), 13 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> 
> diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> new file mode 100644
> index 00000000000..b903e4eb57d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> @@ -0,0 +1,22 @@
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +void link_error ();
> +void g ()
> +{
> +  const char **language_names;
> +
> +  language_names = new const char *[6];
> +
> +  const char **language_names_p = language_names;
> +
> +  language_names_p++;
> +  language_names_p++;
> +  language_names_p++;
> +
> +  if ( (language_names_p) - (language_names+3) != 0)
> +    link_error();
> +  delete[] language_names;
> +}
> +/* We should have removed the link_error on the gimple level as GCC should
> +   be able to tell that language_names_p is the same as language_names+3.  */
> +/* { dg-final { scan-tree-dump-times "link_error" 0 "optimized" } } */
> +
> diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
> index a830bab78ba..e4331c60525 100644
> --- a/gcc/tree-ssa-forwprop.c
> +++ b/gcc/tree-ssa-forwprop.c
> @@ -637,6 +637,47 @@ forward_propagate_into_cond (gimple_stmt_iterator *gsi_p)
>     return 0;
>   }
>   
> +/* Rewrite the DEF_RHS as needed into the (plain) use statement.  */
> +
> +static void
> +rewrite_assign_addr (gimple_stmt_iterator *use_stmt_gsi, tree def_rhs)
> +{
> +  tree def_rhs_base;
> +  poly_int64 def_rhs_offset;
> +
> +  /* Get the base and offset.  */
> +  if ((def_rhs_base = get_addr_base_and_unit_offset (TREE_OPERAND (def_rhs, 0),
> +						     &def_rhs_offset)))
> +    {
> +      tree new_ptr;
> +      poly_offset_int off = 0;
> +
> +      /* If the base was a MEM, then add the offset to the other
> +         offset and adjust the base. */
> +      if (TREE_CODE (def_rhs_base) == MEM_REF)
> +	{
> +	  off += mem_ref_offset (def_rhs_base);
> +	  new_ptr = TREE_OPERAND (def_rhs_base, 0);
> +	}
> +      else
> +	new_ptr = build_fold_addr_expr (def_rhs_base);
> +
> +      /* If we have the new base is not an address express, then use a p+ expression
> +         as the new expression instead of &MEM[x, offset]. */
> +      if (TREE_CODE (new_ptr) != ADDR_EXPR)
> +	{
> +	  tree offset = wide_int_to_tree (sizetype, off);
> +	  def_rhs = build2 (POINTER_PLUS_EXPR, TREE_TYPE (def_rhs), new_ptr, offset);
> +	}
> +    }
> +
> +  /* Replace the rhs with the new expression.  */
> +  def_rhs = unshare_expr (def_rhs);
> +  gimple_assign_set_rhs_from_tree (use_stmt_gsi, def_rhs);
> +  gimple *use_stmt = gsi_stmt (*use_stmt_gsi);
> +  update_stmt (use_stmt);
> +}
> +
>   /* We've just substituted an ADDR_EXPR into stmt.  Update all the
>      relevant data structures to match.  */
>   
> @@ -696,8 +737,8 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
>         if (single_use_p
>   	  && useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE (def_rhs)))
>   	{
> -	  gimple_assign_set_rhs1 (use_stmt, unshare_expr (def_rhs));
> -	  gimple_assign_set_rhs_code (use_stmt, TREE_CODE (def_rhs));
> +	  rewrite_assign_addr (use_stmt_gsi, def_rhs);
> +	  gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
>   	  return true;
>   	}
>   
> @@ -741,14 +782,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
>         if (forward_propagate_addr_expr (lhs, new_def_rhs, single_use_p))
>   	return true;
>   
> -      if (useless_type_conversion_p (TREE_TYPE (lhs),
> -				     TREE_TYPE (new_def_rhs)))
> -	gimple_assign_set_rhs_with_ops (use_stmt_gsi, TREE_CODE (new_def_rhs),
> -					new_def_rhs);
> -      else if (is_gimple_min_invariant (new_def_rhs))
> -	gimple_assign_set_rhs_with_ops (use_stmt_gsi, NOP_EXPR, new_def_rhs);
> -      else
> -	return false;
> +      rewrite_assign_addr (use_stmt_gsi, new_def_rhs);
>         gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
>         update_stmt (use_stmt);
>         return true;
> @@ -951,9 +985,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
>   					      unshare_expr (def_rhs),
>   					      fold_convert (ptr_type_node,
>   							    rhs2)));
> -      gimple_assign_set_rhs_from_tree (use_stmt_gsi, new_rhs);
> -      use_stmt = gsi_stmt (*use_stmt_gsi);
> -      update_stmt (use_stmt);
> +      rewrite_assign_addr (use_stmt_gsi, new_rhs);
>         tidy_after_forward_propagate_addr (use_stmt);
>         return true;
>       }
>
  

On Wed, Oct 27, 2021 at 3:42 AM Richard Biener via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Wed, Oct 27, 2021 at 12:00 PM apinski--- via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > From: Andrew Pinski <apinski@marvell.com>
> >
> > The problem here is tree-ssa-forwprop.c likes to produce
> > &MEM <const char *> [(void *)_4 + 152B] which is the same as
> > _4 p+ 152 which the rest of GCC likes better.
> > This implements this transformation back to pointer plus to
> > improve better code generation later on.
>
> Why do you think so?  Can you pin-point the transform that now
> fixes the new testcase?

So we had originally:
  language_names_p_9 = &MEM <const char *> [(void *)_4 + 24B];
...
  _2 = _4 + 40;
  if (_2 != language_names_p_9)

Forwprop is able to figure out that the above if statement is now
always false as we have (_4 +p 40) != (_4 +p 24) which gets simplified
via a match-and-simplify pattern ().
Does that answer your question?

I will look into the other comments in a new patch.

Thanks,
Andrew

>
> Comments below
>
> > OK? Bootstrapped and tested on aarch64-linux-gnu.
> >
> > Changes from v1:
> > * v2: Add comments.
> >
> > gcc/ChangeLog:
> >
> >         PR tree-optimization/102216
> >         * tree-ssa-forwprop.c (rewrite_assign_addr): New function.
> >         (forward_propagate_addr_expr_1): Use rewrite_assign_addr
> >         when rewriting into the addr_expr into an assignment.
> >
> > gcc/testsuite/ChangeLog:
> >
> >         PR tree-optimization/102216
> >         * g++.dg/tree-ssa/pr102216.C: New test.
> > ---
> >  gcc/testsuite/g++.dg/tree-ssa/pr102216.C | 22 +++++++++
> >  gcc/tree-ssa-forwprop.c                  | 58 ++++++++++++++++++------
> >  2 files changed, 67 insertions(+), 13 deletions(-)
> >  create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> >
> > diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> > new file mode 100644
> > index 00000000000..b903e4eb57d
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> > @@ -0,0 +1,22 @@
> > +/* { dg-options "-O2 -fdump-tree-optimized" } */
> > +void link_error ();
> > +void g ()
> > +{
> > +  const char **language_names;
> > +
> > +  language_names = new const char *[6];
> > +
> > +  const char **language_names_p = language_names;
> > +
> > +  language_names_p++;
> > +  language_names_p++;
> > +  language_names_p++;
> > +
> > +  if ( (language_names_p) - (language_names+3) != 0)
> > +    link_error();
> > +  delete[] language_names;
> > +}
> > +/* We should have removed the link_error on the gimple level as GCC should
> > +   be able to tell that language_names_p is the same as language_names+3.  */
> > +/* { dg-final { scan-tree-dump-times "link_error" 0 "optimized" } } */
> > +
> > diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
> > index a830bab78ba..e4331c60525 100644
> > --- a/gcc/tree-ssa-forwprop.c
> > +++ b/gcc/tree-ssa-forwprop.c
> > @@ -637,6 +637,47 @@ forward_propagate_into_cond (gimple_stmt_iterator *gsi_p)
> >    return 0;
> >  }
> >
> > +/* Rewrite the DEF_RHS as needed into the (plain) use statement.  */
> > +
> > +static void
> > +rewrite_assign_addr (gimple_stmt_iterator *use_stmt_gsi, tree def_rhs)
> > +{
> > +  tree def_rhs_base;
> > +  poly_int64 def_rhs_offset;
> > +
> > +  /* Get the base and offset.  */
> > +  if ((def_rhs_base = get_addr_base_and_unit_offset (TREE_OPERAND (def_rhs, 0),
> > +                                                    &def_rhs_offset)))
>
> So this will cause us to rewrite &MEM[p_1].a.b.c; to a pointer-plus,
> right?  Don't
> we want to preserve that for object-size stuff?  So maybe directly pattern
> match ADDR_EXPR <MEM_REF <SSA_NAME, ..>> only?
>
> > +    {
> > +      tree new_ptr;
> > +      poly_offset_int off = 0;
> > +
> > +      /* If the base was a MEM, then add the offset to the other
> > +         offset and adjust the base. */
> > +      if (TREE_CODE (def_rhs_base) == MEM_REF)
> > +       {
> > +         off += mem_ref_offset (def_rhs_base);
> > +         new_ptr = TREE_OPERAND (def_rhs_base, 0);
> > +       }
> > +      else
> > +       new_ptr = build_fold_addr_expr (def_rhs_base);
> > +
> > +      /* If we have the new base is not an address express, then use a p+ expression
> > +         as the new expression instead of &MEM[x, offset]. */
> > +      if (TREE_CODE (new_ptr) != ADDR_EXPR)
> > +       {
> > +         tree offset = wide_int_to_tree (sizetype, off);
> > +         def_rhs = build2 (POINTER_PLUS_EXPR, TREE_TYPE (def_rhs), new_ptr, offset);
>
> Ick.  You should be able to use gimple_assign_set_rhs_with_ops.
>
> > +       }
> > +    }
> > +
> > +  /* Replace the rhs with the new expression.  */
> > +  def_rhs = unshare_expr (def_rhs);
>
> and definitely no need to unshare anything here?
>
> > +  gimple_assign_set_rhs_from_tree (use_stmt_gsi, def_rhs);
> > +  gimple *use_stmt = gsi_stmt (*use_stmt_gsi);
> > +  update_stmt (use_stmt);
> > +}
> > +
> >  /* We've just substituted an ADDR_EXPR into stmt.  Update all the
> >     relevant data structures to match.  */
> >
> > @@ -696,8 +737,8 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> >        if (single_use_p
> >           && useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE (def_rhs)))
> >         {
> > -         gimple_assign_set_rhs1 (use_stmt, unshare_expr (def_rhs));
> > -         gimple_assign_set_rhs_code (use_stmt, TREE_CODE (def_rhs));
> > +         rewrite_assign_addr (use_stmt_gsi, def_rhs);
> > +         gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
> >           return true;
> >         }
> >
> > @@ -741,14 +782,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> >        if (forward_propagate_addr_expr (lhs, new_def_rhs, single_use_p))
> >         return true;
> >
> > -      if (useless_type_conversion_p (TREE_TYPE (lhs),
> > -                                    TREE_TYPE (new_def_rhs)))
> > -       gimple_assign_set_rhs_with_ops (use_stmt_gsi, TREE_CODE (new_def_rhs),
> > -                                       new_def_rhs);
> > -      else if (is_gimple_min_invariant (new_def_rhs))
> > -       gimple_assign_set_rhs_with_ops (use_stmt_gsi, NOP_EXPR, new_def_rhs);
> > -      else
> > -       return false;
> > +      rewrite_assign_addr (use_stmt_gsi, new_def_rhs);
> >        gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
> >        update_stmt (use_stmt);
> >        return true;
> > @@ -951,9 +985,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> >                                               unshare_expr (def_rhs),
> >                                               fold_convert (ptr_type_node,
> >                                                             rhs2)));
> > -      gimple_assign_set_rhs_from_tree (use_stmt_gsi, new_rhs);
> > -      use_stmt = gsi_stmt (*use_stmt_gsi);
> > -      update_stmt (use_stmt);
> > +      rewrite_assign_addr (use_stmt_gsi, new_rhs);
>
> so you only do this after addr_expr forwarding but not on stmts in
> general?  You could
> do it that way in the 2nd loop over the BB.
>
> >        tidy_after_forward_propagate_addr (use_stmt);
> >        return true;
> >      }
> > --
> > 2.17.1
> >
  

On Mon, Nov 22, 2021 at 9:40 AM Andrew Pinski <pinskia@gmail.com> wrote:
>
> On Wed, Oct 27, 2021 at 3:42 AM Richard Biener via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > On Wed, Oct 27, 2021 at 12:00 PM apinski--- via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > >
> > > From: Andrew Pinski <apinski@marvell.com>
> > >
> > > The problem here is tree-ssa-forwprop.c likes to produce
> > > &MEM <const char *> [(void *)_4 + 152B] which is the same as
> > > _4 p+ 152 which the rest of GCC likes better.
> > > This implements this transformation back to pointer plus to
> > > improve better code generation later on.
> >
> > Why do you think so?  Can you pin-point the transform that now
> > fixes the new testcase?
>
> So we had originally:
>   language_names_p_9 = &MEM <const char *> [(void *)_4 + 24B];
> ...
>   _2 = _4 + 40;

Of course if that would have been

  _2 = &MEM [_4 + 40B];

the issue would be fixed as well.   That said, I agree that _4 + 40
is better but I think we should canonicalize all &MEM[SSA + CST]
this way.  There is a canonicalization phase in fold_stmt_1:

  /* First do required canonicalization of [TARGET_]MEM_REF addresses
     after propagation.
     ???  This shouldn't be done in generic folding but in the
     propagation helpers which also know whether an address was
     propagated.
     Also canonicalize operand order.  */
  switch (gimple_code (stmt))
    {
    case GIMPLE_ASSIGN:
      if (gimple_assign_rhs_class (stmt) == GIMPLE_SINGLE_RHS)
        {
          tree *rhs = gimple_assign_rhs1_ptr (stmt);
          if ((REFERENCE_CLASS_P (*rhs)
               || TREE_CODE (*rhs) == ADDR_EXPR)
              && maybe_canonicalize_mem_ref_addr (rhs))
            changed = true;

where this could be done (apart from adding a match.pd pattern for this).

>   if (_2 != language_names_p_9)
>
> Forwprop is able to figure out that the above if statement is now
> always false as we have (_4 +p 40) != (_4 +p 24) which gets simplified
> via a match-and-simplify pattern ().
> Does that answer your question?
>
> I will look into the other comments in a new patch.
>
> Thanks,
> Andrew
>
> >
> > Comments below
> >
> > > OK? Bootstrapped and tested on aarch64-linux-gnu.
> > >
> > > Changes from v1:
> > > * v2: Add comments.
> > >
> > > gcc/ChangeLog:
> > >
> > >         PR tree-optimization/102216
> > >         * tree-ssa-forwprop.c (rewrite_assign_addr): New function.
> > >         (forward_propagate_addr_expr_1): Use rewrite_assign_addr
> > >         when rewriting into the addr_expr into an assignment.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > >         PR tree-optimization/102216
> > >         * g++.dg/tree-ssa/pr102216.C: New test.
> > > ---
> > >  gcc/testsuite/g++.dg/tree-ssa/pr102216.C | 22 +++++++++
> > >  gcc/tree-ssa-forwprop.c                  | 58 ++++++++++++++++++------
> > >  2 files changed, 67 insertions(+), 13 deletions(-)
> > >  create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> > >
> > > diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> > > new file mode 100644
> > > index 00000000000..b903e4eb57d
> > > --- /dev/null
> > > +++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> > > @@ -0,0 +1,22 @@
> > > +/* { dg-options "-O2 -fdump-tree-optimized" } */
> > > +void link_error ();
> > > +void g ()
> > > +{
> > > +  const char **language_names;
> > > +
> > > +  language_names = new const char *[6];
> > > +
> > > +  const char **language_names_p = language_names;
> > > +
> > > +  language_names_p++;
> > > +  language_names_p++;
> > > +  language_names_p++;
> > > +
> > > +  if ( (language_names_p) - (language_names+3) != 0)
> > > +    link_error();
> > > +  delete[] language_names;
> > > +}
> > > +/* We should have removed the link_error on the gimple level as GCC should
> > > +   be able to tell that language_names_p is the same as language_names+3.  */
> > > +/* { dg-final { scan-tree-dump-times "link_error" 0 "optimized" } } */
> > > +
> > > diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
> > > index a830bab78ba..e4331c60525 100644
> > > --- a/gcc/tree-ssa-forwprop.c
> > > +++ b/gcc/tree-ssa-forwprop.c
> > > @@ -637,6 +637,47 @@ forward_propagate_into_cond (gimple_stmt_iterator *gsi_p)
> > >    return 0;
> > >  }
> > >
> > > +/* Rewrite the DEF_RHS as needed into the (plain) use statement.  */
> > > +
> > > +static void
> > > +rewrite_assign_addr (gimple_stmt_iterator *use_stmt_gsi, tree def_rhs)
> > > +{
> > > +  tree def_rhs_base;
> > > +  poly_int64 def_rhs_offset;
> > > +
> > > +  /* Get the base and offset.  */
> > > +  if ((def_rhs_base = get_addr_base_and_unit_offset (TREE_OPERAND (def_rhs, 0),
> > > +                                                    &def_rhs_offset)))
> >
> > So this will cause us to rewrite &MEM[p_1].a.b.c; to a pointer-plus,
> > right?  Don't
> > we want to preserve that for object-size stuff?  So maybe directly pattern
> > match ADDR_EXPR <MEM_REF <SSA_NAME, ..>> only?
> >
> > > +    {
> > > +      tree new_ptr;
> > > +      poly_offset_int off = 0;
> > > +
> > > +      /* If the base was a MEM, then add the offset to the other
> > > +         offset and adjust the base. */
> > > +      if (TREE_CODE (def_rhs_base) == MEM_REF)
> > > +       {
> > > +         off += mem_ref_offset (def_rhs_base);
> > > +         new_ptr = TREE_OPERAND (def_rhs_base, 0);
> > > +       }
> > > +      else
> > > +       new_ptr = build_fold_addr_expr (def_rhs_base);
> > > +
> > > +      /* If we have the new base is not an address express, then use a p+ expression
> > > +         as the new expression instead of &MEM[x, offset]. */
> > > +      if (TREE_CODE (new_ptr) != ADDR_EXPR)
> > > +       {
> > > +         tree offset = wide_int_to_tree (sizetype, off);
> > > +         def_rhs = build2 (POINTER_PLUS_EXPR, TREE_TYPE (def_rhs), new_ptr, offset);
> >
> > Ick.  You should be able to use gimple_assign_set_rhs_with_ops.
> >
> > > +       }
> > > +    }
> > > +
> > > +  /* Replace the rhs with the new expression.  */
> > > +  def_rhs = unshare_expr (def_rhs);
> >
> > and definitely no need to unshare anything here?
> >
> > > +  gimple_assign_set_rhs_from_tree (use_stmt_gsi, def_rhs);
> > > +  gimple *use_stmt = gsi_stmt (*use_stmt_gsi);
> > > +  update_stmt (use_stmt);
> > > +}
> > > +
> > >  /* We've just substituted an ADDR_EXPR into stmt.  Update all the
> > >     relevant data structures to match.  */
> > >
> > > @@ -696,8 +737,8 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> > >        if (single_use_p
> > >           && useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE (def_rhs)))
> > >         {
> > > -         gimple_assign_set_rhs1 (use_stmt, unshare_expr (def_rhs));
> > > -         gimple_assign_set_rhs_code (use_stmt, TREE_CODE (def_rhs));
> > > +         rewrite_assign_addr (use_stmt_gsi, def_rhs);
> > > +         gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
> > >           return true;
> > >         }
> > >
> > > @@ -741,14 +782,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> > >        if (forward_propagate_addr_expr (lhs, new_def_rhs, single_use_p))
> > >         return true;
> > >
> > > -      if (useless_type_conversion_p (TREE_TYPE (lhs),
> > > -                                    TREE_TYPE (new_def_rhs)))
> > > -       gimple_assign_set_rhs_with_ops (use_stmt_gsi, TREE_CODE (new_def_rhs),
> > > -                                       new_def_rhs);
> > > -      else if (is_gimple_min_invariant (new_def_rhs))
> > > -       gimple_assign_set_rhs_with_ops (use_stmt_gsi, NOP_EXPR, new_def_rhs);
> > > -      else
> > > -       return false;
> > > +      rewrite_assign_addr (use_stmt_gsi, new_def_rhs);
> > >        gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
> > >        update_stmt (use_stmt);
> > >        return true;
> > > @@ -951,9 +985,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> > >                                               unshare_expr (def_rhs),
> > >                                               fold_convert (ptr_type_node,
> > >                                                             rhs2)));
> > > -      gimple_assign_set_rhs_from_tree (use_stmt_gsi, new_rhs);
> > > -      use_stmt = gsi_stmt (*use_stmt_gsi);
> > > -      update_stmt (use_stmt);
> > > +      rewrite_assign_addr (use_stmt_gsi, new_rhs);
> >
> > so you only do this after addr_expr forwarding but not on stmts in
> > general?  You could
> > do it that way in the 2nd loop over the BB.
> >
> > >        tidy_after_forward_propagate_addr (use_stmt);
> > >        return true;
> > >      }
> > > --
> > > 2.17.1
> > >
  

On Mon, Nov 22, 2021 at 3:40 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Mon, Nov 22, 2021 at 9:40 AM Andrew Pinski <pinskia@gmail.com> wrote:
> >
> > On Wed, Oct 27, 2021 at 3:42 AM Richard Biener via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > >
> > > On Wed, Oct 27, 2021 at 12:00 PM apinski--- via Gcc-patches
> > > <gcc-patches@gcc.gnu.org> wrote:
> > > >
> > > > From: Andrew Pinski <apinski@marvell.com>
> > > >
> > > > The problem here is tree-ssa-forwprop.c likes to produce
> > > > &MEM <const char *> [(void *)_4 + 152B] which is the same as
> > > > _4 p+ 152 which the rest of GCC likes better.
> > > > This implements this transformation back to pointer plus to
> > > > improve better code generation later on.
> > >
> > > Why do you think so?  Can you pin-point the transform that now
> > > fixes the new testcase?
> >
> > So we had originally:
> >   language_names_p_9 = &MEM <const char *> [(void *)_4 + 24B];
> > ...
> >   _2 = _4 + 40;
>
> Of course if that would have been
>
>   _2 = &MEM [_4 + 40B];
>
> the issue would be fixed as well.   That said, I agree that _4 + 40
> is better but I think we should canonicalize all &MEM[SSA + CST]
> this way.  There is a canonicalization phase in fold_stmt_1:
>
>   /* First do required canonicalization of [TARGET_]MEM_REF addresses
>      after propagation.
>      ???  This shouldn't be done in generic folding but in the
>      propagation helpers which also know whether an address was
>      propagated.
>      Also canonicalize operand order.  */
>   switch (gimple_code (stmt))
>     {
>     case GIMPLE_ASSIGN:
>       if (gimple_assign_rhs_class (stmt) == GIMPLE_SINGLE_RHS)
>         {
>           tree *rhs = gimple_assign_rhs1_ptr (stmt);
>           if ((REFERENCE_CLASS_P (*rhs)
>                || TREE_CODE (*rhs) == ADDR_EXPR)
>               && maybe_canonicalize_mem_ref_addr (rhs))
>             changed = true;
>
> where this could be done (apart from adding a match.pd pattern for this).

Yes that is a good idea, I now have a patch which I am testing to add
this canonicalization. It is actually simpler than the previous patch
too.

Thanks,
Andrew

>
> >   if (_2 != language_names_p_9)
> >
> > Forwprop is able to figure out that the above if statement is now
> > always false as we have (_4 +p 40) != (_4 +p 24) which gets simplified
> > via a match-and-simplify pattern ().
> > Does that answer your question?
> >
> > I will look into the other comments in a new patch.
> >
> > Thanks,
> > Andrew
> >
> > >
> > > Comments below
> > >
> > > > OK? Bootstrapped and tested on aarch64-linux-gnu.
> > > >
> > > > Changes from v1:
> > > > * v2: Add comments.
> > > >
> > > > gcc/ChangeLog:
> > > >
> > > >         PR tree-optimization/102216
> > > >         * tree-ssa-forwprop.c (rewrite_assign_addr): New function.
> > > >         (forward_propagate_addr_expr_1): Use rewrite_assign_addr
> > > >         when rewriting into the addr_expr into an assignment.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > >         PR tree-optimization/102216
> > > >         * g++.dg/tree-ssa/pr102216.C: New test.
> > > > ---
> > > >  gcc/testsuite/g++.dg/tree-ssa/pr102216.C | 22 +++++++++
> > > >  gcc/tree-ssa-forwprop.c                  | 58 ++++++++++++++++++------
> > > >  2 files changed, 67 insertions(+), 13 deletions(-)
> > > >  create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> > > >
> > > > diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> > > > new file mode 100644
> > > > index 00000000000..b903e4eb57d
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
> > > > @@ -0,0 +1,22 @@
> > > > +/* { dg-options "-O2 -fdump-tree-optimized" } */
> > > > +void link_error ();
> > > > +void g ()
> > > > +{
> > > > +  const char **language_names;
> > > > +
> > > > +  language_names = new const char *[6];
> > > > +
> > > > +  const char **language_names_p = language_names;
> > > > +
> > > > +  language_names_p++;
> > > > +  language_names_p++;
> > > > +  language_names_p++;
> > > > +
> > > > +  if ( (language_names_p) - (language_names+3) != 0)
> > > > +    link_error();
> > > > +  delete[] language_names;
> > > > +}
> > > > +/* We should have removed the link_error on the gimple level as GCC should
> > > > +   be able to tell that language_names_p is the same as language_names+3.  */
> > > > +/* { dg-final { scan-tree-dump-times "link_error" 0 "optimized" } } */
> > > > +
> > > > diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
> > > > index a830bab78ba..e4331c60525 100644
> > > > --- a/gcc/tree-ssa-forwprop.c
> > > > +++ b/gcc/tree-ssa-forwprop.c
> > > > @@ -637,6 +637,47 @@ forward_propagate_into_cond (gimple_stmt_iterator *gsi_p)
> > > >    return 0;
> > > >  }
> > > >
> > > > +/* Rewrite the DEF_RHS as needed into the (plain) use statement.  */
> > > > +
> > > > +static void
> > > > +rewrite_assign_addr (gimple_stmt_iterator *use_stmt_gsi, tree def_rhs)
> > > > +{
> > > > +  tree def_rhs_base;
> > > > +  poly_int64 def_rhs_offset;
> > > > +
> > > > +  /* Get the base and offset.  */
> > > > +  if ((def_rhs_base = get_addr_base_and_unit_offset (TREE_OPERAND (def_rhs, 0),
> > > > +                                                    &def_rhs_offset)))
> > >
> > > So this will cause us to rewrite &MEM[p_1].a.b.c; to a pointer-plus,
> > > right?  Don't
> > > we want to preserve that for object-size stuff?  So maybe directly pattern
> > > match ADDR_EXPR <MEM_REF <SSA_NAME, ..>> only?
> > >
> > > > +    {
> > > > +      tree new_ptr;
> > > > +      poly_offset_int off = 0;
> > > > +
> > > > +      /* If the base was a MEM, then add the offset to the other
> > > > +         offset and adjust the base. */
> > > > +      if (TREE_CODE (def_rhs_base) == MEM_REF)
> > > > +       {
> > > > +         off += mem_ref_offset (def_rhs_base);
> > > > +         new_ptr = TREE_OPERAND (def_rhs_base, 0);
> > > > +       }
> > > > +      else
> > > > +       new_ptr = build_fold_addr_expr (def_rhs_base);
> > > > +
> > > > +      /* If we have the new base is not an address express, then use a p+ expression
> > > > +         as the new expression instead of &MEM[x, offset]. */
> > > > +      if (TREE_CODE (new_ptr) != ADDR_EXPR)
> > > > +       {
> > > > +         tree offset = wide_int_to_tree (sizetype, off);
> > > > +         def_rhs = build2 (POINTER_PLUS_EXPR, TREE_TYPE (def_rhs), new_ptr, offset);
> > >
> > > Ick.  You should be able to use gimple_assign_set_rhs_with_ops.
> > >
> > > > +       }
> > > > +    }
> > > > +
> > > > +  /* Replace the rhs with the new expression.  */
> > > > +  def_rhs = unshare_expr (def_rhs);
> > >
> > > and definitely no need to unshare anything here?
> > >
> > > > +  gimple_assign_set_rhs_from_tree (use_stmt_gsi, def_rhs);
> > > > +  gimple *use_stmt = gsi_stmt (*use_stmt_gsi);
> > > > +  update_stmt (use_stmt);
> > > > +}
> > > > +
> > > >  /* We've just substituted an ADDR_EXPR into stmt.  Update all the
> > > >     relevant data structures to match.  */
> > > >
> > > > @@ -696,8 +737,8 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> > > >        if (single_use_p
> > > >           && useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE (def_rhs)))
> > > >         {
> > > > -         gimple_assign_set_rhs1 (use_stmt, unshare_expr (def_rhs));
> > > > -         gimple_assign_set_rhs_code (use_stmt, TREE_CODE (def_rhs));
> > > > +         rewrite_assign_addr (use_stmt_gsi, def_rhs);
> > > > +         gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
> > > >           return true;
> > > >         }
> > > >
> > > > @@ -741,14 +782,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> > > >        if (forward_propagate_addr_expr (lhs, new_def_rhs, single_use_p))
> > > >         return true;
> > > >
> > > > -      if (useless_type_conversion_p (TREE_TYPE (lhs),
> > > > -                                    TREE_TYPE (new_def_rhs)))
> > > > -       gimple_assign_set_rhs_with_ops (use_stmt_gsi, TREE_CODE (new_def_rhs),
> > > > -                                       new_def_rhs);
> > > > -      else if (is_gimple_min_invariant (new_def_rhs))
> > > > -       gimple_assign_set_rhs_with_ops (use_stmt_gsi, NOP_EXPR, new_def_rhs);
> > > > -      else
> > > > -       return false;
> > > > +      rewrite_assign_addr (use_stmt_gsi, new_def_rhs);
> > > >        gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
> > > >        update_stmt (use_stmt);
> > > >        return true;
> > > > @@ -951,9 +985,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
> > > >                                               unshare_expr (def_rhs),
> > > >                                               fold_convert (ptr_type_node,
> > > >                                                             rhs2)));
> > > > -      gimple_assign_set_rhs_from_tree (use_stmt_gsi, new_rhs);
> > > > -      use_stmt = gsi_stmt (*use_stmt_gsi);
> > > > -      update_stmt (use_stmt);
> > > > +      rewrite_assign_addr (use_stmt_gsi, new_rhs);
> > >
> > > so you only do this after addr_expr forwarding but not on stmts in
> > > general?  You could
> > > do it that way in the 2nd loop over the BB.
> > >
> > > >        tidy_after_forward_propagate_addr (use_stmt);
> > > >        return true;
> > > >      }
> > > > --
> > > > 2.17.1
> > > >