Hi, Richard. Would you mind take a look at this patch?
This is a proposal patch (We could add more testcase for ARM in the future).
But we want to know if this patch is a correct approach to achieve what we want.
In RVV (RISC-V Vector), we have a bunch of instructions:
vadd.vx/vsub.vx/vmul.vx......etc.
Such instructions allows CPU do the operations between vector and scalar
directly without any vector duplicate or broadcast instruction.
So this patch is quite important for RVV auto-vectorizaton support which can
reduce a lot of gimple IR pattern.
I known GCC 13 is not the appropriate for this patch, we hope this can be done
in GCC 14.
Thank you so much.
juzhe.zh...@rivai.ai
From: lehua.ding
Date: 2023-01-13 17:42
To: gcc-patches
CC: richard.sandiford; juzhe.zhong; Lehua Ding
Subject: [PATCH 1/1] [fwprop]: Add the support of forwarding the vec_duplicate
rtx
From: Lehua Ding <lehua.d...@rivai.ai>
ps: Resend for adjusting the width of each line of text.
Hi,
When I was adding the new RISC-V auto-vectorization function, I found that
converting `vector-reg1 vop vector-vreg2` to `scalar-reg3 vop vectorreg2`
is not very easy to handle where `vector-reg1` is a vec_duplicate_expr.
For example the bellow gimple IR:
```gimple
<bb2>
vect_cst__51 = [vec_duplicate_expr] z_14(D);
<bb 3>
vect_iftmp.13_53 = .LEN_COND_ADD(mask__40.9_47, vect__6.12_50, vect_cst__51, {
0.0, ... }, curr_cnt_60);
```
I once wanted to add corresponding functions to gimple IR, such as adding
.LEN_COND_ADD_VS, and then convert .LEN_COND_ADD to .LEN_COND_ADD_VS in
match.pd.
This method can be realized, but it will cause too many similar internal
functions
to be added to gimple IR. It doesn't feel necessary. Later, I tried to combine
them
on the combine pass but failed. Finally, I thought of adding the ability to
support
forwarding `(vec_duplciate reg)` in fwprop pass, so I have this patch.
Because the current upstream does not support the RISC-V automatic vectorization
function, I found an example in sve that can also be optimized and simply tried
it. For the float type, one instruction can be reduced, for example the bellow C
code. The difference between the new and old assembly code is that the new one
uses the mov instruction to directly move the scalar variable to the vector
register.
The old assembly code first moves the scalar variable to the vector register
outside
the loop, and then uses the sel instruction. Compared with the entire assembly
code,
the new assembly code has one instruction less. In addition, I noticed that some
instructions in the new assembly code are ahead of the `ble .L1` instruction.
I debugged and found that the modification was made in the ce1 pass. This pass
believes that moving up is more beneficial to performance.
In addition, for the int type, compared with the float type, the new assembly
code
will have one more `fmov s2, w2` instruction, so I can't judge whether the
performance is better than the previous one. In fact, I mainly do RISC-V
development work.
This patch is an exploratory patch and has not been tested too much. I mainly
want to see your suggestions on whether this method is feasible and possible
potential problems.
Best,
Lehua Ding
```c
/* compiler options: -O3 -march=armv8.2-a+sve -S */
void test1 (int *pred, float *x, float z, int n)
{
for (int i = 0; i < n; i += 1)
{
x[i] = pred[i] != 1 ? x[i] : z;
}
}
```
The old assembly code like this (compiler explorer link:
https://godbolt.org/z/hxTnEhaqY):
```asm
test1:
cmp w2, 0
ble.L1
mov x3, 0
cntw x4
mov z0.s, s0
whilelo p0.s, wzr, w2
ptrue p2.b, all
.L3:
ld1w z2.s, p0/z, [x0, x3, lsl 2]
ld1w z1.s, p0/z, [x1, x3, lsl 2]
cmpne p1.s, p2/z, z2.s, #1
sel z1.s, p1, z1.s, z0.s
st1w z1.s, p0, [x1, x3, lsl 2]
add x3, x3, x4
while lo p0.s, w3, w2
b.any.L3
.L1:
ret
```
The new assembly code like this:
```asm
test1:
whilelo p0.s, wzr, w2
mov x3, 0
cntw x4
ptrue p2.b, all
cmp w2, 0
ble.L1
.L3:
ld1w z2.s, p0/z, [x0, x3, lsl 2]
ld1w z1.s, p0/z, [x1, x3, lsl 2]
cmpne p1.s, p2/z, z2.s, #1
mov z1.s, p1/m, s0
st1w z1.s, p0, [x1, x3, lsl 2]
add x3, x3, x4
while lo p0.s, w3, w2
b.any.L3
.L1:
ret
```
gcc/ChangeLog:
* config/aarch64/aarch64-sve.md (@aarch64_sel_dup<mode>_vs): Add new
pattern to capture new opeands order
* fwprop.cc (fwprop_propagation::profitable_p): Add new check
(reg_single_def_for_src_p): Add new function for src rtx
(forward_propagate_into): Change to new function call
---
gcc/config/aarch64/aarch64-sve.md | 20 ++++++++++++++++++++
gcc/fwprop.cc | 16 +++++++++++++++-
2 files changed, 35 insertions(+), 1 deletion(-)
diff --git a/gcc/config/aarch64/aarch64-sve.md
b/gcc/config/aarch64/aarch64-sve.md
index b8cc47ef5fc..84d8ed0924d 100644
--- a/gcc/config/aarch64/aarch64-sve.md
+++ b/gcc/config/aarch64/aarch64-sve.md
@@ -7636,6 +7636,26 @@
[(set_attr "movprfx" "*,*,yes,yes,yes,yes")]
)
+;; Swap the order of operand 1 and operand 2 so that it matches the above
pattern
+(define_insn_and_split "@aarch64_sel_dup<mode>_vs"
+ [(set (match_operand:SVE_ALL 0 "register_operand" "=?w, w, ??w, ?&w, ??&w,
?&w")
+ (unspec:SVE_ALL
+ [(match_operand:<VPRED> 3 "register_operand" "Upl, Upl, Upl, Upl, Upl, Upl")
+ (match_operand:SVE_ALL 1 "aarch64_simd_reg_or_zero" "0, 0, Dz, Dz,
w, w")
+ (vec_duplicate:SVE_ALL
+ (match_operand:<VEL> 2 "register_operand" "r, w, r, w, r, w"))]
+ UNSPEC_SEL))]
+ "TARGET_SVE"
+ "#"
+ "&& 1"
+ [(set (match_dup 0)
+ (unspec:SVE_ALL
+ [(match_dup 3)
+ (vec_duplicate:SVE_ALL (match_dup 2))
+ (match_dup 1)]
+ UNSPEC_SEL))]
+)
+
;; -------------------------------------------------------------------------
;; ---- [INT,FP] Compare and select
;; -------------------------------------------------------------------------
diff --git a/gcc/fwprop.cc b/gcc/fwprop.cc
index ae342f59407..5d921dd3d2f 100644
--- a/gcc/fwprop.cc
+++ b/gcc/fwprop.cc
@@ -342,6 +342,9 @@ fwprop_propagation::profitable_p () const
if (CONSTANT_P (to))
return true;
+ if (GET_CODE (to) == VEC_DUPLICATE)
+ return true;
+
return false;
}
@@ -353,6 +356,17 @@ reg_single_def_p (rtx x)
return REG_P (x) && crtl->ssa->single_dominating_def (REGNO (x));
}
+/* Check that X has a single def or a VEC_DUPLICATE expr whose elements have a
+ single def. */
+static bool
+reg_single_def_for_src_p (rtx x)
+{
+ if (GET_CODE (x) == VEC_DUPLICATE)
+ x = XEXP (x, 0);
+
+ return reg_single_def_p (x);
+}
+
/* Return true if X contains a paradoxical subreg. */
static bool
@@ -873,7 +887,7 @@ forward_propagate_into (use_info *use, bool reg_prop_only =
false)
if ((reg_prop_only
|| (def_loop != use_loop
&& !flow_loop_nested_p (use_loop, def_loop)))
- && (!reg_single_def_p (dest) || !reg_single_def_p (src)))
+ && (!reg_single_def_p (dest) || !reg_single_def_for_src_p (src)))
return false;
/* Don't substitute into a non-local goto, this confuses CFG. */
--
2.36.3
