Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> The following makes sure to rewrite arithmetic with undefined behavior
> on overflow to a well-defined variant when moving them to be always
> executed as part of doing if-conversion for loop vectorization.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> Any comments?
LGTM FWIW, although…
> Thanks,
> Richard.
>
> 2021-10-11 Richard Biener <rguent...@suse.de>
>
> PR tree-optimization/102659
> * tree-if-conv.c (need_to_rewrite_undefined): New flag.
> (if_convertible_gimple_assign_stmt_p): Mark the loop for
> rewrite when stmts with undefined behavior on integer
> overflow appear.
> (combine_blocks): Predicate also when we need to rewrite stmts.
> (predicate_statements): Rewrite affected stmts to something
> with well-defined behavior on overflow.
> (tree_if_conversion): Initialize need_to_rewrite_undefined.
>
> * gcc.dg/torture/pr69760.c: Adjust the testcase.
> * gcc.target/i386/avx2-vect-mask-store-move1.c: Expect to move
> the conversions to unsigned as well.
> ---
> gcc/testsuite/gcc.dg/torture/pr69760.c | 3 +-
> .../i386/avx2-vect-mask-store-move1.c | 2 +-
> gcc/tree-if-conv.c | 28 ++++++++++++++++++-
> 3 files changed, 29 insertions(+), 4 deletions(-)
>
> diff --git a/gcc/testsuite/gcc.dg/torture/pr69760.c
> b/gcc/testsuite/gcc.dg/torture/pr69760.c
> index 53733c7c6a4..47e01ae59bd 100644
> --- a/gcc/testsuite/gcc.dg/torture/pr69760.c
> +++ b/gcc/testsuite/gcc.dg/torture/pr69760.c
> @@ -1,11 +1,10 @@
> /* PR tree-optimization/69760 */
> /* { dg-do run { target { { *-*-linux* *-*-gnu* *-*-uclinux* } && mmap } } }
> */
> -/* { dg-options "-O2" } */
>
> #include <unistd.h>
> #include <sys/mman.h>
>
> -__attribute__((noinline, noclone)) void
> +__attribute__((noinline, noclone)) static void
> test_func (double *a, int L, int m, int n, int N)
> {
> int i, k;
> diff --git a/gcc/testsuite/gcc.target/i386/avx2-vect-mask-store-move1.c
> b/gcc/testsuite/gcc.target/i386/avx2-vect-mask-store-move1.c
> index 989ba402e0e..6a47a09c835 100644
> --- a/gcc/testsuite/gcc.target/i386/avx2-vect-mask-store-move1.c
> +++ b/gcc/testsuite/gcc.target/i386/avx2-vect-mask-store-move1.c
> @@ -78,4 +78,4 @@ avx2_test (void)
> abort ();
> }
>
> -/* { dg-final { scan-tree-dump-times "Move stmt to created bb" 6 "vect" } }
> */
> +/* { dg-final { scan-tree-dump-times "Move stmt to created bb" 10 "vect" } }
> */
> diff --git a/gcc/tree-if-conv.c b/gcc/tree-if-conv.c
> index d7b7b309309..6a67acfeaae 100644
> --- a/gcc/tree-if-conv.c
> +++ b/gcc/tree-if-conv.c
> @@ -132,6 +132,11 @@ along with GCC; see the file COPYING3. If not see
> predicate_statements for the kinds of predication we support. */
> static bool need_to_predicate;
>
> +/* True if we have to rewrite stmts that may invoke undefined behavior
> + when a condition C was false so it doesn't if it is always executed.
> + See predicate_statements for the kinds of predication we support. */
> +static bool need_to_rewrite_undefined;
> +
> /* Indicate if there are any complicated PHIs that need to be handled in
> if-conversion. Complicated PHI has more than two arguments and can't
> be degenerated to two arguments PHI. See more information in comment
> @@ -1042,6 +1047,12 @@ if_convertible_gimple_assign_stmt_p (gimple *stmt,
> fprintf (dump_file, "tree could trap...\n");
> return false;
> }
> + else if (INTEGRAL_TYPE_P (TREE_TYPE (lhs))
> + && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (lhs))
> + && arith_code_with_undefined_signed_overflow
> + (gimple_assign_rhs_code (stmt)))
> + /* We have to rewrite stmts with undefined overflow. */
> + need_to_rewrite_undefined = true;
>
> /* When if-converting stores force versioning, likewise if we
> ended up generating store data races. */
> @@ -2563,6 +2574,20 @@ predicate_statements (loop_p loop)
>
> gsi_replace (&gsi, new_stmt, true);
> }
> + else if (INTEGRAL_TYPE_P (TREE_TYPE (gimple_assign_lhs (stmt)))
> + && TYPE_OVERFLOW_UNDEFINED
> + (TREE_TYPE (gimple_assign_lhs (stmt)))
> + && arith_code_with_undefined_signed_overflow
> + (gimple_assign_rhs_code (stmt)))
> + {
> + gsi_remove (&gsi, true);
> + gsi_insert_seq_before (&gsi, rewrite_to_defined_overflow (stmt),
> + GSI_SAME_STMT);
> + if (gsi_end_p (gsi))
> + gsi = gsi_last_bb (gimple_bb (stmt));
> + else
> + gsi_prev (&gsi);
…perhaps there should be a GSI_* for this idiom.
Thanks,
Richard
> + }
> else if (gimple_vdef (stmt))
> {
> tree lhs = gimple_assign_lhs (stmt);
> @@ -2647,7 +2672,7 @@ combine_blocks (class loop *loop)
> insert_gimplified_predicates (loop);
> predicate_all_scalar_phis (loop);
>
> - if (need_to_predicate)
> + if (need_to_predicate || need_to_rewrite_undefined)
> predicate_statements (loop);
>
> /* Merge basic blocks. */
> @@ -3148,6 +3173,7 @@ tree_if_conversion (class loop *loop, vec<gimple *>
> *preds)
> rloop = NULL;
> ifc_bbs = NULL;
> need_to_predicate = false;
> + need_to_rewrite_undefined = false;
> any_complicated_phi = false;
>
> /* Apply more aggressive if-conversion when loop or its outer loop were
