f6d787c231
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.
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