https://gcc.gnu.org/g:3918bea620e826b0df68a9c8492b791a67f294b5
commit r15-1959-g3918bea620e826b0df68a9c8492b791a67f294b5
Author: Pan Li <pan2...@intel.com>
Date: Sun Jun 30 10:55:50 2024 +0800
Vect: Optimize truncation for .SAT_SUB operands
To get better vectorized code of .SAT_SUB, we would like to avoid the
truncated operation for the assignment. For example, as below.
unsigned int _1;
unsigned int _2;
unsigned short int _4;
_9 = (unsigned short int).SAT_SUB (_1, _2);
If we make sure that the _1 is in the range of unsigned short int. Such
as a def similar to:
_1 = (unsigned short int)_4;
Then we can do the distribute the truncation operation to:
_3 = (unsigned short int) MIN (65535, _2); // aka _3 = .SAT_TRUNC (_2);
_9 = .SAT_SUB (_4, _3);
Then, we can better vectorized code and avoid the unnecessary narrowing
stmt during vectorization with below stmt(s).
_3 = .SAT_TRUNC(_2); // SI => HI
_9 = .SAT_SUB (_4, _3);
Let's take RISC-V vector as example to tell the changes. For below
sample code:
__attribute__((noinline))
void test (uint16_t *x, unsigned b, unsigned n)
{
unsigned a = 0;
uint16_t *p = x;
do {
a = *--p;
*p = (uint16_t)(a >= b ? a - b : 0);
} while (--n);
}
Before this patch:
...
.L3:
vle16.v v1,0(a3)
vrsub.vx v5,v2,t1
mv t3,a4
addw a4,a4,t5
vrgather.vv v3,v1,v5
vsetvli zero,zero,e32,m1,ta,ma
vzext.vf2 v1,v3
vssubu.vx v1,v1,a1
vsetvli zero,zero,e16,mf2,ta,ma
vncvt.x.x.w v1,v1
vrgather.vv v3,v1,v5
vse16.v v3,0(a3)
sub a3,a3,t4
bgtu t6,a4,.L3
...
After this patch:
test:
...
.L3:
vle16.v v3,0(a3)
vrsub.vx v5,v2,a6
mv a7,a4
addw a4,a4,t3
vrgather.vv v1,v3,v5
vssubu.vv v1,v1,v6
vrgather.vv v3,v1,v5
vse16.v v3,0(a3)
sub a3,a3,t1
bgtu t4,a4,.L3
...
The below test suites are passed for this patch:
1. The rv64gcv fully regression tests.
2. The rv64gcv build with glibc.
3. The x86 bootstrap tests.
4. The x86 fully regression tests.
gcc/ChangeLog:
* tree-vect-patterns.cc (vect_recog_sat_sub_pattern_transform):
Add new func impl to perform the truncation distribution.
(vect_recog_sat_sub_pattern): Perform above optimize before
generate .SAT_SUB call.
Signed-off-by: Pan Li <pan2...@intel.com>
Diff:
---
gcc/tree-vect-patterns.cc | 65 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 65 insertions(+)
diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 86e893a1c433..4570c25b6647 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -4566,6 +4566,70 @@ vect_recog_sat_add_pattern (vec_info *vinfo,
stmt_vec_info stmt_vinfo,
return NULL;
}
+/*
+ * Try to transform the truncation for .SAT_SUB pattern, mostly occurs in
+ * the benchmark zip. Aka:
+ *
+ * unsigned int _1;
+ * unsigned int _2;
+ * unsigned short int _4;
+ * _9 = (unsigned short int).SAT_SUB (_1, _2);
+ *
+ * if _1 is known to be in the range of unsigned short int. For example
+ * there is a def _1 = (unsigned short int)_4. Then we can transform the
+ * truncation to:
+ *
+ * _3 = (unsigned short int) MIN (65535, _2); // aka _3 = .SAT_TRUNC (_2);
+ * _9 = .SAT_SUB (_4, _3);
+ *
+ * Then, we can better vectorized code and avoid the unnecessary narrowing
+ * stmt during vectorization with below stmt(s).
+ *
+ * _3 = .SAT_TRUNC(_2); // SI => HI
+ * _9 = .SAT_SUB (_4, _3);
+ */
+static void
+vect_recog_sat_sub_pattern_transform (vec_info *vinfo,
+ stmt_vec_info stmt_vinfo,
+ tree lhs, tree *ops)
+{
+ tree otype = TREE_TYPE (lhs);
+ tree itype = TREE_TYPE (ops[0]);
+ unsigned itype_prec = TYPE_PRECISION (itype);
+ unsigned otype_prec = TYPE_PRECISION (otype);
+
+ if (types_compatible_p (otype, itype) || otype_prec >= itype_prec)
+ return;
+
+ tree v_otype = get_vectype_for_scalar_type (vinfo, otype);
+ tree v_itype = get_vectype_for_scalar_type (vinfo, itype);
+ tree_pair v_pair = tree_pair (v_otype, v_itype);
+
+ if (v_otype == NULL_TREE || v_itype == NULL_TREE
+ || !direct_internal_fn_supported_p (IFN_SAT_TRUNC, v_pair,
+ OPTIMIZE_FOR_BOTH))
+ return;
+
+ /* 1. Find the _4 and update ops[0] as above example. */
+ vect_unpromoted_value unprom;
+ tree tmp = vect_look_through_possible_promotion (vinfo, ops[0], &unprom);
+
+ if (tmp == NULL_TREE || TYPE_PRECISION (unprom.type) != otype_prec)
+ return;
+
+ ops[0] = tmp;
+
+ /* 2. Generate _3 = .SAT_TRUNC (_2) and update ops[1] as above example. */
+ tree trunc_lhs_ssa = vect_recog_temp_ssa_var (otype, NULL);
+ gcall *call = gimple_build_call_internal (IFN_SAT_TRUNC, 1, ops[1]);
+
+ gimple_call_set_lhs (call, trunc_lhs_ssa);
+ gimple_call_set_nothrow (call, /* nothrow_p */ false);
+ append_pattern_def_seq (vinfo, stmt_vinfo, call, v_otype);
+
+ ops[1] = trunc_lhs_ssa;
+}
+
/*
* Try to detect saturation sub pattern (SAT_ADD), aka below gimple:
* _7 = _1 >= _2;
@@ -4591,6 +4655,7 @@ vect_recog_sat_sub_pattern (vec_info *vinfo,
stmt_vec_info stmt_vinfo,
if (gimple_unsigned_integer_sat_sub (lhs, ops, NULL))
{
+ vect_recog_sat_sub_pattern_transform (vinfo, stmt_vinfo, lhs, ops);
gimple *stmt = vect_recog_build_binary_gimple_stmt (vinfo, stmt_vinfo,
IFN_SAT_SUB, type_out,
lhs, ops[0], ops[1]);
