Hi,
On Thu, 27 Aug 2020 at 10:04, Richard Biener wrote:
>
> This makes sure to put special-ops expanded rhs left where
> expression rewrite expects it.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
>
> 2020-08-27 Richard Biener
>
> PR tree-optimization/96579
> * tree-ssa-reassoc.c (linearize_expr_tree): If we expand
> rhs via special ops make sure to swap operands.
>
> * gcc.dg/pr96579.c: New testcase.
> ---
> gcc/testsuite/gcc.dg/pr96579.c | 4
> gcc/tree-ssa-reassoc.c | 13 +++--
> 2 files changed, 15 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/pr96579.c
>
> diff --git a/gcc/testsuite/gcc.dg/pr96579.c b/gcc/testsuite/gcc.dg/pr96579.c
> new file mode 100644
> index 000..49fdcb40359
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr96579.c
> @@ -0,0 +1,4 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fno-tree-forwprop -ffast-math -fno-tree-vrp" } */
> +
> +#include "pr96370.c"
pr96370 has
/* { dg-do compile { target dfp } } */
which is needed here too, otherwise the test fails on arm/aarch64 and others.
I've pushed the obvious fix.
Christophe
> diff --git a/gcc/tree-ssa-reassoc.c b/gcc/tree-ssa-reassoc.c
> index fed463b0350..a5f5d52edab 100644
> --- a/gcc/tree-ssa-reassoc.c
> +++ b/gcc/tree-ssa-reassoc.c
> @@ -5651,13 +5651,20 @@ linearize_expr_tree (vec *ops,
> gimple *stmt,
>
>if (!binrhsisreassoc)
> {
> - if (!try_special_add_to_ops (ops, rhscode, binrhs, binrhsdef))
> + bool swap = false;
> + if (try_special_add_to_ops (ops, rhscode, binrhs, binrhsdef))
> + /* If we add ops for the rhs we expect to be able to recurse
> + to it via the lhs during expression rewrite so swap
> + operands. */
> + swap = true;
> + else
> add_to_ops_vec (ops, binrhs);
>
> if (!try_special_add_to_ops (ops, rhscode, binlhs, binlhsdef))
> add_to_ops_vec (ops, binlhs);
>
> - return;
> + if (!swap)
> + return;
> }
>
>if (dump_file && (dump_flags & TDF_DETAILS))
> @@ -5676,6 +5683,8 @@ linearize_expr_tree (vec *ops, gimple
> *stmt,
> fprintf (dump_file, " is now ");
> print_gimple_stmt (dump_file, stmt, 0);
> }
> + if (!binrhsisreassoc)
> + return;
>
>/* We want to make it so the lhs is always the reassociative op,
> so swap. */
> --
> 2.26.2
