On Sun, Sep 3, 2023 at 6:19 PM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> This improves rewrite_to_defined_overflow slightly if we already
> have an unsigned type. The only place where this seems to show up
> is ifcombine. It removes one extra statement which gets added and
> then later on removed.
What specific case is that? It sounds like we call the function when
it isn't needed? I also think that refactoring to a special case when
the LHS type already is OK will result in better code in the end.
Richard.
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.
>
> gcc/ChangeLog:
>
> PR tree-optimization/111276
> * gimple-fold.cc (rewrite_to_defined_overflow): Don't
> add a new lhs if we already the unsigned type.
> ---
> gcc/gimple-fold.cc | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
> index fd01810581a..2fcafeada37 100644
> --- a/gcc/gimple-fold.cc
> +++ b/gcc/gimple-fold.cc
> @@ -8721,10 +8721,19 @@ rewrite_to_defined_overflow (gimple *stmt, bool
> in_place /* = false */)
> op = gimple_convert (&stmts, type, op);
> gimple_set_op (stmt, i, op);
> }
> - gimple_assign_set_lhs (stmt, make_ssa_name (type, stmt));
> + bool needs_cast_back = false;
> + if (!useless_type_conversion_p (type, TREE_TYPE (lhs)))
> + {
> + gimple_assign_set_lhs (stmt, make_ssa_name (type, stmt));
> + needs_cast_back = true;
> + }
> +
> if (gimple_assign_rhs_code (stmt) == POINTER_PLUS_EXPR)
> gimple_assign_set_rhs_code (stmt, PLUS_EXPR);
> - gimple_set_modified (stmt, true);
> +
> + if (needs_cast_back || stmts)
> + gimple_set_modified (stmt, true);
> +
> if (in_place)
> {
> gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
> @@ -8734,6 +8743,10 @@ rewrite_to_defined_overflow (gimple *stmt, bool
> in_place /* = false */)
> }
> else
> gimple_seq_add_stmt (&stmts, stmt);
> +
> + if (!needs_cast_back)
> + return stmts;
> +
> gimple *cvt = gimple_build_assign (lhs, NOP_EXPR, gimple_assign_lhs
> (stmt));
> if (in_place)
> {
> --
> 2.31.1
>
