> -----Original Message-----
> From: Richard Biener <[email protected]>
> Sent: 23 June 2026 14:22
> To: Victor Do Nascimento <[email protected]>
> Cc: [email protected]; Saurabh Jha <[email protected]>; Tamar
> Christina <[email protected]>
> Subject: Re: [PATCH] tree-opt: Remove redundant VEC_COND_EXPR
> statements for dot product [PR111770]
>
> On Tue, 23 Jun 2026, Victor Do Nascimento wrote:
>
> > Consider the following dot-product computation:
> >
> > uint32_t
> > tcp_checksum(int n, uint8_t* data)
> > {
> > uint32_t sum = 0;
> > for (int i=0; i<n; i+=1)
> > sum += data[i] * data[i];
> > return sum;
> > }
> >
> > At present, following vectorization and the subsequent optimization
> > passes, we will end up with the following GIMPLE code:
> >
> > vect__1 = .MASK_LOAD (vectp_data, 8B, loop_mask_1, { 0, ... });
> > masked_op1_1 = VEC_COND_EXPR <loop_mask_1, vect__1, { 0, ... }>;
> > vect_patt_1 = DOT_PROD_EXPR <vect__1, masked_op1_1, vectt_sum_1>;
> >
> > By looking at the input data going into the VEC_COND_EXPR, its mask
> > and its else value, we can walk back up the USE-DEF chain to see
> > whether the source of the input data shares the same mask and else
> > values. If so, we can safely remove the VEC_COND_EXPR statement from
> > the cfg, thus resulting in the more optimal variant:
> >
> > vect__1 = .MASK_LOAD (vectp_data, 8B, loop_mask_1, { 0, ... });
> > vect_patt_1 = DOT_PROD_EXPR <vect__1, vect__1, vectt_sum_1>;
> >
> > Regression testes on AArch64 & x86_64, no new regressions.
>
> I think this belongs into forwprop. We might be able to do
> a match.pd pattern as well, sth like
>
> (simplify
> (vec_cond @0 @1 @2)
> (if (same_mask_and_else_value (@0, @1, @2))
> @1))
>
> where an external same_mask_and_else_value function would look
> at the def of @1. Similar situations can occur with
> .COND_<op>
We already do something similar in match.pd
/* Detect cases in which a VEC_COND_EXPR effectively replaces the
"else" value of an IFN_COND_*. */
(for cond_op (COND_BINARY)
So there's some precedence for doing this there already.
Thanks,
Tamar
>
> Richard.
>
> > PR tree-optimization/111770
> >
> > gcc/ChangeLog:
> >
> > * gimple-isel.cc (stmt_is_any_masked_load_p): New.
> > (stmt_is_vec_cond_expr_zeroing): Likewise.
> > (redundant_condexpr_removal): Likewise.
> > (pass_gimple_isel::execute): Add call to
> > `redundant_condexpr_removal'.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.dg/vect/vect-cond-dot.c: New.
> > ---
> > gcc/gimple-isel.cc | 78 +++++++++++++++++++++++
> > gcc/testsuite/gcc.dg/vect/vect-cond-dot.c | 21 ++++++
> > 2 files changed, 99 insertions(+)
> > create mode 100644 gcc/testsuite/gcc.dg/vect/vect-cond-dot.c
> >
> > diff --git a/gcc/gimple-isel.cc b/gcc/gimple-isel.cc
> > index b193e27b183..aa020f402e0 100644
> > --- a/gcc/gimple-isel.cc
> > +++ b/gcc/gimple-isel.cc
> > @@ -1343,6 +1343,82 @@ gimple_isel_builtin_call (gcall *call,
> gimple_stmt_iterator *gsi)
> > }
> > }
> >
> > +static internal_fn
> > +stmt_is_any_masked_load_p (gimple *stmt)
> > +{
> > + if (stmt && is_gimple_call (stmt) && gimple_call_internal_p (stmt))
> > + {
> > + internal_fn ifn = gimple_call_internal_fn (stmt);
> > + if (internal_load_fn_p (gimple_call_internal_fn (stmt))
> > + && internal_fn_mask_index (ifn) >= 0)
> > + return ifn;
> > + }
> > + return IFN_LAST;
> > +}
> > +
> > +/* Ensure we have a statement of the form:
> > + VEC_COND_EXPR <mask, then_val, { 0, ... }>
> > + If the else value of STMT is a zero initializer, return the then value,
> > + returning NULL_TREE otherwise. */
> > +static tree
> > +stmt_is_vec_cond_expr_zeroing (gimple *stmt)
> > +{
> > + if (is_gimple_assign (stmt))
> > + {
> > + enum tree_code code = gimple_assign_rhs_code (stmt);
> > + if (code == VEC_COND_EXPR)
> > + {
> > + tree then_val = gimple_assign_rhs2 (stmt);
> > + tree else_val = gimple_assign_rhs3 (stmt);
> > + if (initializer_zerop (else_val))
> > + return then_val;
> > + }
> > + }
> > + return NULL_TREE;
> > +}
> > +
> > + /* Remove redundant VEC_COND_EXPR statments.
> > + Consider the following set of statements:
> > +
> > + vect__1 = .MASK_LOAD (vectp_data, 8B, loop_mask_1, { 0, ... });
> > + masked_op1_1 = VEC_COND_EXPR <loop_mask_1, vect__1, { 0, ... }>;
> > + vect_patt_1 = DOT_PROD_EXPR <vect__1, masked_op1_1 vect
> > +
> > + By looking at the input data going into the VEC_COND_EXPR, we can
> walk
> > + back up the USE-DEF chain to see whether the source of the input data
> > + shares the same mask and else values. If so, we can safely remove the
> > + VEC_COND_EXPR statement from the cfg. */
> > +static void
> > +redundant_condexpr_removal (gimple_stmt_iterator &gsi)
> > +{
> > +
> > + gimple *vcond_stmt = *gsi;
> > + tree then_val = stmt_is_vec_cond_expr_zeroing (vcond_stmt);
> > + if (then_val && TREE_CODE (then_val) == SSA_NAME)
> > + {
> > + gimple *then_defn = SSA_NAME_DEF_STMT (then_val);
> > + internal_fn then_ifn = stmt_is_any_masked_load_p (then_defn);
> > + if (then_ifn != IFN_LAST)
> > + {
> > + tree vcond_mask, load_mask, load_else;
> > + vcond_mask = gimple_assign_rhs1 (vcond_stmt);
> > + load_mask = gimple_call_arg (then_defn,
> > + internal_fn_mask_index (then_ifn));
> > + load_else = gimple_call_arg (then_defn,
> > + internal_fn_else_index (then_ifn));
> > + if (vcond_mask == load_mask && initializer_zerop (load_else))
> > + {
> > + tree dest = gimple_assign_lhs (gsi_stmt (gsi));
> > + replace_uses_by (dest, then_val);
> > + gimple *def_stmt = gsi_stmt (gsi);
> > + gsi_remove (&gsi, true);
> > + release_defs (def_stmt);
> > + }
> > + }
> > + }
> > +}
> > +
> > +
> > /* Iterate all gimple statements and perform pre RTL expansion
> > GIMPLE massaging to improve instruction selection. */
> >
> > @@ -1360,6 +1436,8 @@ pass_gimple_isel::execute (struct function *fun)
> > /* Give the target first try at replacing the instruction. */
> > cfg_changed |= targetm.instruction_selection (fun, &gsi);
> >
> > + redundant_condexpr_removal (gsi);
> > +
> > /* Pre-expand VEC_COND_EXPRs to .VCOND* internal function
> > calls mapping to supported optabs. */
> > gimple *g = gimple_expand_vec_cond_expr (&gsi);
> > diff --git a/gcc/testsuite/gcc.dg/vect/vect-cond-dot.c
> b/gcc/testsuite/gcc.dg/vect/vect-cond-dot.c
> > new file mode 100644
> > index 00000000000..7b6d920c9e5
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/vect/vect-cond-dot.c
> > @@ -0,0 +1,21 @@
> > +/* { dg-do compile } */
> > +/* { dg-additional-options "-fdump-tree-optimized" } */
> > +/* { dg-require-effective-target vect_masked_load } */
> > +#include <stdint.h>
> > +
> > +#define CHECK_DOT(IN, OUT) \
> > +OUT check_dot_##OUT(int n, IN* data) { \
> > + OUT sum = 0; \
> > + for (int i=0; i<n; i+=1) { \
> > + sum += data[i] * data[i]; \
> > + } \
> > + return sum; \
> > +}
> > +
> > +CHECK_DOT (uint8_t, uint32_t);
> > +CHECK_DOT (int8_t, int32_t);
> > +CHECK_DOT (int16_t, int64_t);
> > +
> > +/* { dg-final { scan-tree-dump-times {vectorized 1 loops} 3 "vect" } } */
> > +/* { dg-final { scan-tree-dump-times {[\n\r]\s*(vect__[^ \t=]+) =
> \.MASK_LOAD \([a-zA-Z0-9_.]+, [0-9]+B, (loop_mask_[0-9]+), \{ 0, \.\.\.
> \}\);.*[\n\r]\s+masked_op[^ \t=]+ = VEC_COND_EXPR <\2, \1, \{ 0, \.\.\. \}} 9
> "vect" { target aarch64*-*-* } } } */
> > +/* { dg-final { scan-tree-dump-not {VEC_COND_EXPR} "optimized" } } */
> >
>
> --
> Richard Biener <[email protected]>
> SUSE Software Solutions Germany GmbH,
> Frankenstrasse 146, 90461 Nuernberg, Germany;
> GF: Jochen Jaser, Andrew McDonald, Werner Knoblich; (HRB 36809, AG
> Nuernberg)
