>
>
> > Am 09.09.2025 um 12:54 schrieb Juergen Christ <jchr...@linux.ibm.com>:
> >
> > The length returned by vect_get_loop_len is REALLEN + BIAS, but was
> > assumed to be REALLEN - BIAS. If BIAS is -1, this leads to wrong
> > code.
> >
> > Bootstrapped and regtested on s390. Ok for trunk?
>
> Ok. Can you also test on ppc64le which IIRC uses different bias?
Yes, ppc64le uses 0 as bias. Successfully bootstrapped and regtested
on ppc64le.
> Thanks,
> Richard
>
> > gcc/ChangeLog:
> >
> > * tree-vect-loop.cc (vectorizable_live_operation_1): Fix
> > load/store bias handling.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.dg/vect/nodump-extractlast-1.c: New test.
> >
> > Signed-off-by: Juergen Christ <jchr...@linux.ibm.com>
> > ---
> > .../gcc.dg/vect/nodump-extractlast-1.c | 21 ++++++++++++++++++
> > gcc/tree-vect-loop.cc | 22 ++++++++++---------
> > 2 files changed, 33 insertions(+), 10 deletions(-)
> > create mode 100644 gcc/testsuite/gcc.dg/vect/nodump-extractlast-1.c
> >
> > diff --git a/gcc/testsuite/gcc.dg/vect/nodump-extractlast-1.c
> > b/gcc/testsuite/gcc.dg/vect/nodump-extractlast-1.c
> > new file mode 100644
> > index 000000000000..980ac3e42188
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/vect/nodump-extractlast-1.c
> > @@ -0,0 +1,21 @@
> > +/* Check for a bung in the treatment of LOOP_VINFO_PARTIAL_LOAD_STORE_BIAS
> > when
> > + using VEC_EXTRACT. */
> > +/* { dg-require-effective-target vect_int } */
> > +
> > +char c = 4;
> > +
> > +__attribute__((noipa))
> > +int
> > +foo ()
> > +{
> > + for ( ; c > 3; c -= 3);
> > + return c - 1;
> > +}
> > +
> > +int
> > +main ()
> > +{
> > + if (foo() != 0)
> > + __builtin_abort();
> > + return 0;
> > +}
> > diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> > index 3b56f865ec7c..78256904dcea 100644
> > --- a/gcc/tree-vect-loop.cc
> > +++ b/gcc/tree-vect-loop.cc
> > @@ -10155,10 +10155,12 @@ vectorizable_live_operation_1 (loop_vec_info
> > loop_vinfo, basic_block exit_bb,
> > {
> > /* Emit:
> >
> > - SCALAR_RES = VEC_EXTRACT <VEC_LHS, LEN + BIAS - 1>
> > + SCALAR_RES = VEC_EXTRACT <VEC_LHS, LEN - (BIAS + 1)>
> >
> > - where VEC_LHS is the vectorized live-out result and MASK is
> > - the loop mask for the final iteration. */
> > + where VEC_LHS is the vectorized live-out result, LEN is the length of
> > + the vector, BIAS is the load-store bias. The bias should not be used
> > + at all since we are not using load/store operations, but LEN will be
> > + REALLEN + BIAS, so subtract it to get to the correct position. */
> > gcc_assert (SLP_TREE_LANES (slp_node) == 1);
> > gimple_seq tem = NULL;
> > gimple_stmt_iterator gsi = gsi_last (tem);
> > @@ -10167,18 +10169,18 @@ vectorizable_live_operation_1 (loop_vec_info
> > loop_vinfo, basic_block exit_bb,
> > 1, vectype, 0, 1);
> > gimple_seq_add_seq (&stmts, tem);
> >
> > - /* BIAS - 1. */
> > + /* BIAS + 1. */
> > signed char biasval = LOOP_VINFO_PARTIAL_LOAD_STORE_BIAS (loop_vinfo);
> > - tree bias_minus_one
> > - = int_const_binop (MINUS_EXPR,
> > + tree bias_plus_one
> > + = int_const_binop (PLUS_EXPR,
> > build_int_cst (TREE_TYPE (len), biasval),
> > build_one_cst (TREE_TYPE (len)));
> >
> > - /* LAST_INDEX = LEN + (BIAS - 1). */
> > - tree last_index = gimple_build (&stmts, PLUS_EXPR, TREE_TYPE (len),
> > - len, bias_minus_one);
> > + /* LAST_INDEX = LEN - (BIAS + 1). */
> > + tree last_index = gimple_build (&stmts, MINUS_EXPR, TREE_TYPE (len),
> > + len, bias_plus_one);
> >
> > - /* SCALAR_RES = VEC_EXTRACT <VEC_LHS, LEN + BIAS - 1>. */
> > + /* SCALAR_RES = VEC_EXTRACT <VEC_LHS, LEN - (BIAS + 1)>. */
> > tree scalar_res
> > = gimple_build (&stmts, CFN_VEC_EXTRACT, TREE_TYPE (vectype),
> > vec_lhs_phi, last_index);
> > --
> > 2.43.7
> >
