For parameter passing through stack, vectorized load from parm_decl
in callee may trigger serious STF issue. This is why GCC12 regresses
50% for cray at -O2 compared to GCC11.
The patch add an extremely large number to stmt_cost to prevent
vectorization for loads from parm_decl under very-cheap cost model,
this can at least prevent O2 regression due to STF issue, but may lose
some perf where there's no such issue(1 vector_load vs n scalar_load +
CTOR).
No impact for SPEC2017 for both plain O2 and native O2 on ICX.
Bootstrapped and regtested on x86_64-linux-gnu{-m32,}.
Ok for trunk?
gcc/ChangeLog:
PR target/101908
* config/i386/i386.cc (ix86_load_maybe_stfs_p): New.
(ix86_vector_costs::add_stmt_cost): Add extra cost for
vector_load/unsigned_load which may have stall forward issue.
gcc/testsuite/ChangeLog:
* gcc.target/i386/pr101908-1.c: New test.
* gcc.target/i386/pr101908-2.c: New test.
---
gcc/config/i386/i386.cc | 31 ++++++++++++++++++++++
gcc/testsuite/gcc.target/i386/pr101908-1.c | 12 +++++++++
gcc/testsuite/gcc.target/i386/pr101908-2.c | 12 +++++++++
3 files changed, 55 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/i386/pr101908-1.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr101908-2.c
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index b2bf90576d5..3bbaaf65ea8 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -22976,6 +22976,19 @@ ix86_noce_conversion_profitable_p (rtx_insn *seq,
struct noce_if_info *if_info)
return default_noce_conversion_profitable_p (seq, if_info);
}
+/* Return true if REF may have STF issue, otherwise false. */
+static bool
+ix86_load_maybe_stfs_p (tree ref)
+{
+ tree addr = get_base_address (ref);
+
+ if (TREE_CODE (addr) != PARM_DECL
+ || !tree_fits_uhwi_p (TYPE_SIZE (TREE_TYPE (addr)))
+ || tree_to_uhwi (TYPE_SIZE (TREE_TYPE (addr))) <= MAX_BITS_PER_WORD)
+ return false;
+ return true;
+}
+
/* x86-specific vector costs. */
class ix86_vector_costs : public vector_costs
{
@@ -23203,6 +23216,24 @@ ix86_vector_costs::add_stmt_cost (int count,
vect_cost_for_stmt kind,
if (TREE_CODE (op) == SSA_NAME)
TREE_VISITED (op) = 0;
}
+
+ /* Prevent vectorization for load from parm_decl at O2 to avoid STF issue.
+ Performance may lose when there's no STF issue(1 vector_load vs n
+ scalar_load + CTOR).
+ TODO: both extra cost(2000) and ix86_load_maybe_stfs_p need to be fine
+ tuned. */
+ if ((kind == vector_load || kind == unaligned_load)
+ && flag_vect_cost_model == VECT_COST_MODEL_VERY_CHEAP
+ && stmt_info
+ && stmt_info->slp_type == pure_slp
+ && stmt_info->stmt
+ && gimple_assign_load_p (stmt_info->stmt)
+ && ix86_load_maybe_stfs_p (gimple_assign_rhs1 (stmt_info->stmt)))
+ {
+ stmt_cost = ix86_builtin_vectorization_cost (kind, vectype, misalign);
+ stmt_cost += 2000;
+ }
+
if (stmt_cost == -1)
stmt_cost = ix86_builtin_vectorization_cost (kind, vectype, misalign);
diff --git a/gcc/testsuite/gcc.target/i386/pr101908-1.c
b/gcc/testsuite/gcc.target/i386/pr101908-1.c
new file mode 100644
index 00000000000..f8e0f2e26bb
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr101908-1.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-slp-details" } */
+/* { dg-final { scan-tree-dump {(?n)add new stmt:.*MEM \<vector\(2\) double\>}
"slp2" } } */
+
+struct X { double x[2]; };
+typedef double v2df __attribute__((vector_size(16)));
+
+v2df __attribute__((noipa))
+foo (struct X* x, struct X* y)
+{
+ return (v2df) {x->x[1], x->x[0] } + (v2df) { y->x[1], y->x[0] };
+}
diff --git a/gcc/testsuite/gcc.target/i386/pr101908-2.c
b/gcc/testsuite/gcc.target/i386/pr101908-2.c
new file mode 100644
index 00000000000..7f2f00cebab
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr101908-2.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-slp-details" } */
+/* { dg-final { scan-tree-dump-not {(?n)add new stmt:.*MEM \<vector\(2\)
double\>} "slp2" } } */
+
+struct X { double x[2]; };
+typedef double v2df __attribute__((vector_size(16)));
+
+v2df __attribute__((noipa))
+foo (struct X x, struct X y)
+{
+ return (v2df) {x.x[1], x.x[0] } + (v2df) { y.x[1], y.x[0] };
+}
--
2.18.1
