On 27 October 2021 11:59:58 CEST, apinski--- via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>From: Andrew Pinski <apin...@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;
> }
