Hi, before this patch, a simple conversion case for RVV codegen:
foo:
ble a2,zero,.L8
addiw a5,a2,-1
li a4,6
bleu a5,a4,.L6
srliw a3,a2,3
slli a3,a3,3
add a3,a3,a0
mv a5,a0
mv a4,a1
vsetivli zero,8,e16,m1,ta,ma
.L4:
vle8.v v2,0(a5)
addi a5,a5,8
vzext.vf2 v1,v2
vse16.v v1,0(a4)
addi a4,a4,16
bne a3,a5,.L4
andi a5,a2,-8
beq a2,a5,.L10
.L3:
slli a4,a5,32
srli a4,a4,32
subw a2,a2,a5
slli a2,a2,32
slli a5,a4,1
srli a2,a2,32
add a0,a0,a4
add a1,a1,a5
vsetvli zero,a2,e16,m1,ta,ma
vle8.v v2,0(a0)
vzext.vf2 v1,v2
vse16.v v1,0(a1)
.L8:
ret
.L10:
ret
.L6:
li a5,0
j .L3
This vectorization go through first loop:
vsetivli zero,8,e16,m1,ta,ma
.L4:
vle8.v v2,0(a5)
addi a5,a5,8
vzext.vf2 v1,v2
vse16.v v1,0(a4)
addi a4,a4,16
bne a3,a5,.L4
Each iteration processes 8 elements.
For a scalable vectorization with VLEN > 128 bits CPU, it's ok when VLEN = 128.
But, as long as VLEN > 128 bits, it will waste the CPU resources. That is, e.g.
VLEN = 256bits.
only half of the vector units are working and another half is idle.
After investigation, I realize that I forgot to adjust COST for SELECT_VL.
So, adjust COST for SELECT_VL styple length vectorization. We adjust COST from
3 to 2. since
after this patch:
foo:
ble a2,zero,.L5
.L3:
vsetvli a5,a2,e16,m1,ta,ma -----> SELECT_VL cost.
vle8.v v2,0(a0)
slli a4,a5,1 -----> additional shift of outcome
SELECT_VL for memory address calculation.
vzext.vf2 v1,v2
sub a2,a2,a5
vse16.v v1,0(a1)
add a0,a0,a5
add a1,a1,a4
bne a2,zero,.L3
.L5:
ret
This patch is a simple fix that I previous forgot.
Ok for trunk ?
If not, I am going to adjust cost in backend cost model.
PR target/111317
gcc/ChangeLog:
* tree-vect-loop.cc (vect_estimate_min_profitable_iters): Adjust for
COST for decrement IV.
gcc/testsuite/ChangeLog:
* gcc.dg/vect/costmodel/riscv/rvv/pr111317.c: New test.
---
.../gcc.dg/vect/costmodel/riscv/rvv/pr111317.c | 12 ++++++++++++
gcc/tree-vect-loop.cc | 17 ++++++++++++++---
2 files changed, 26 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/vect/costmodel/riscv/rvv/pr111317.c
diff --git a/gcc/testsuite/gcc.dg/vect/costmodel/riscv/rvv/pr111317.c
b/gcc/testsuite/gcc.dg/vect/costmodel/riscv/rvv/pr111317.c
new file mode 100644
index 00000000000..d4bea242a9a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/costmodel/riscv/rvv/pr111317.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O3 -ftree-vectorize
--param=riscv-autovec-lmul=m1" } */
+
+void
+foo (char *__restrict a, short *__restrict b, int n)
+{
+ for (int i = 0; i < n; i++)
+ b[i] = (short) a[i];
+}
+
+/* { dg-final { scan-assembler-times
{vsetvli\s+[a-x0-9]+,\s*[a-x0-9]+,\s*e16,\s*m1,\s*t[au],\s*m[au]} 1 } } */
+/* { dg-final { scan-assembler-times {vsetvli} 1 } } */
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 6261cd1be1d..19e38b8637b 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -4870,10 +4870,21 @@ vect_estimate_min_profitable_iters (loop_vec_info
loop_vinfo,
if (partial_load_store_bias != 0)
body_stmts += 1;
- /* Each may need two MINs and one MINUS to update lengths in body
- for next iteration. */
+ unsigned int length_update_cost = 0;
+ if (LOOP_VINFO_USING_DECREMENTING_IV_P (loop_vinfo))
+ /* For decrement IV style, we use a single SELECT_VL since
+ beginning to calculate the number of elements need to be
+ processed in current iteration, and a SHIFT operation to
+ compute the next memory address instead of adding vectorization
+ factor. */
+ length_update_cost = 2;
+ else
+ /* For increment IV stype, Each may need two MINs and one MINUS to
+ update lengths in body for next iteration. */
+ length_update_cost = 3;
+
if (need_iterate_p)
- body_stmts += 3 * num_vectors;
+ body_stmts += length_update_cost * num_vectors;
}
(void) add_stmt_cost (target_cost_data, prologue_stmts,
--
2.36.3
