LGTM.
juzhe.zh...@rivai.ai
From: Robin Dapp
Date: 2025-08-04 17:09
To: gcc-patches
CC: kito.ch...@gmail.com; juzhe.zh...@rivai.ai; jeffreya...@gmail.com;
pan2...@intel.com; rdapp....@gmail.com
Subject: [PATCH] RISC-V: Expand const_vector with 2 elts per pattern.
Hi,
In PR121334 we are asked to expand a const_vector of size 4 with
poly_int elements. It has 2 elts per pattern so is neither a
const_vector_duplicate nor a const_vector_stepped.
We don't allow this kind of constant in legitimate_constant_p but expr
apparently still wants us to expand it under certain conditions.
This patch implements a basic expander for such kinds of patterns.
As slide1up is used to build the individual vectors it also adds
a helper function expand_slide1up.
I regtested on rv64gcv_zvl512b but unfortunately the newly created pattern is
not even executed. I tried some variations of the original code but didn't
manage to trigger it.
Regards
Robin
PR target/121334
gcc/ChangeLog:
* config/riscv/riscv-v.cc (expand_slide1up): New function.
(expand_vector_init_trailing_same_elem): Use new function.
(expand_const_vector_onestep): New function.
(expand_const_vector): Uew expand_slide1up.
(expand_vector_init_merge_repeating_sequence): Ditto.
(shuffle_off_by_one_patterns): Ditto.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/rvv/autovec/pr121334.c: New test.
---
gcc/config/riscv/riscv-v.cc | 123 +++++++++++++++---
.../gcc.target/riscv/rvv/autovec/pr121334.c | 10 ++
2 files changed, 116 insertions(+), 17 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr121334.c
diff --git a/gcc/config/riscv/riscv-v.cc b/gcc/config/riscv/riscv-v.cc
index 6424399b343..f50358528d4 100644
--- a/gcc/config/riscv/riscv-v.cc
+++ b/gcc/config/riscv/riscv-v.cc
@@ -954,6 +954,26 @@ emit_vlmax_masked_gather_mu_insn (rtx target, rtx op, rtx
sel, rtx mask)
emit_vlmax_insn (icode, BINARY_OP_TAMU, ops);
}
+/* Function to emit a vslide1up instruction of mode MODE with destination
+ DEST and slideup element ELT. */
+
+rtx
+expand_slide1up (machine_mode mode, rtx dest, rtx elt)
+{
+ unsigned int unspec
+ = FLOAT_MODE_P (mode) ? UNSPEC_VFSLIDE1UP : UNSPEC_VSLIDE1UP;
+ insn_code icode = code_for_pred_slide (unspec, mode);
+ /* RVV Spec 16.3.1
+ The destination vector register group for vslideup cannot overlap the
+ source vector register group, otherwise the instruction encoding
+ is reserved. Thus, we need a new register. */
+ rtx tmp = gen_reg_rtx (mode);
+ rtx ops[] = {tmp, dest, elt};
+ emit_vlmax_insn (icode, BINARY_OP, ops);
+ return tmp;
+}
+
+
/* According to RVV ISA spec (16.5.1. Synthesizing vdecompress):
https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc
@@ -1175,16 +1195,7 @@ expand_vector_init_trailing_same_elem (rtx target,
{
rtx dup = expand_vector_broadcast (mode, builder.elt (nelts_reqd - 1));
for (int i = nelts_reqd - trailing_ndups - 1; i >= 0; i--)
- {
- unsigned int unspec
- = FLOAT_MODE_P (mode) ? UNSPEC_VFSLIDE1UP : UNSPEC_VSLIDE1UP;
- insn_code icode = code_for_pred_slide (unspec, mode);
- rtx tmp = gen_reg_rtx (mode);
- rtx ops[] = {tmp, dup, builder.elt (i)};
- emit_vlmax_insn (icode, BINARY_OP, ops);
- /* slide1up need source and dest to be different REG. */
- dup = tmp;
- }
+ dup = expand_slide1up (mode, dup, builder.elt (i));
emit_move_insn (target, dup);
return true;
@@ -1717,6 +1728,77 @@ expand_const_vector_stepped (rtx target, rtx src,
rvv_builder *builder)
gcc_unreachable ();
}
+/* We don't actually allow this case in legitimate_constant_p but
+ the middle-end still expects us to handle it in an expander
+ (see PR121334). This is assumed to happen very rarely so the
+ implementation is not very efficient, particularly
+ for short vectors.
+*/
+
+static void
+expand_const_vector_onestep (rtx target, rvv_builder &builder)
+{
+ machine_mode mode = GET_MODE (target);
+ gcc_assert (GET_MODE_CLASS (mode) == MODE_VECTOR_INT);
+ gcc_assert (builder.nelts_per_pattern () == 2);
+
+ /* We have n encoded patterns
+ {csta_0, cstb_0},
+ {csta_1, cstb_1},
+ ...
+ {csta_{n-1}, cstb_{n-1}}
+ which should become one vector:
+ {csta_0, csta_1, ..., csta_{n-1},
+ cstb_0, cstb_1, ..., cstb_{n-1},
+ ...
+ cstb_0, cstb_1, ..., cstb_{n-1}}.
+
+ In order to achieve this we create a permute/gather constant
+ sel = {0, 1, ..., n - 1, 0, 1, ..., n - 1, ...}
+ and two vectors
+ va = {csta_0, csta_1, ..., csta_{n-1}},
+ vb = {cstb_0, cstb_1, ..., cstb_{n-1}}.
+
+ Then we use a VLMAX gather to "broadcast" vb and afterwards
+ overwrite the first n elements with va. */
+
+ int n = builder.npatterns ();
+ /* { 0, 1, 2, ..., n - 1 }. */
+ rtx vid = gen_reg_rtx (mode);
+ expand_vec_series (vid, const0_rtx, const1_rtx);
+
+ /* { 0, 1, ..., n - 1, 0, 1, ..., n - 1, ... }. */
+ rtx sel = gen_reg_rtx (mode);
+ rtx and_ops[] = {sel, vid, GEN_INT (n)};
+ emit_vlmax_insn (code_for_pred_scalar (AND, mode), BINARY_OP, and_ops);
+
+ /* va = { ELT (0), ELT (1), ... ELT (n - 1) }. */
+ rtx tmp1 = gen_reg_rtx (mode);
+ rtx ops1[] = {tmp1, builder.elt (0)};
+ expand_broadcast (mode, ops1);
+ for (int i = 1; i < n; i++)
+ tmp1 = expand_slide1up (mode, tmp1, builder.elt (i));
+
+ /* vb = { ELT (n), ELT (n + 1), ... ELT (2 * n - 1) }. */
+ rtx tmp2 = gen_reg_rtx (mode);
+ rtx ops2[] = {tmp2, builder.elt (n)};
+ expand_broadcast (mode, ops2);
+ for (int i = 1; i < n; i++)
+ tmp2 = expand_slide1up (mode, tmp2, builder.elt (n + i));
+
+ /* Duplicate vb. */
+ rtx tmp3 = gen_reg_rtx (mode);
+ emit_vlmax_gather_insn (tmp3, tmp2, sel);
+
+ /* Overwrite the first n - 1 elements with va. */
+ rtx dest = gen_reg_rtx (mode);
+ insn_code icode = code_for_pred_mov (mode);
+ rtx ops3[] = {dest, tmp3, tmp1};
+ emit_nonvlmax_insn (icode, __MASK_OP_TUMA | UNARY_OP_P, ops3, GEN_INT (n));
+
+ emit_move_insn (target, dest);
+}
+
static void
expand_const_vector (rtx target, rtx src)
{
@@ -1744,6 +1826,8 @@ expand_const_vector (rtx target, rtx src)
if (CONST_VECTOR_DUPLICATE_P (src))
return expand_const_vector_duplicate (target, &builder);
+ else if (CONST_VECTOR_NELTS_PER_PATTERN (src) == 2)
+ return expand_const_vector_onestep (target, builder);
else if (CONST_VECTOR_STEPPED_P (src))
return expand_const_vector_stepped (target, src, &builder);
@@ -2648,8 +2732,14 @@ expand_vector_init_merge_repeating_sequence (rtx target,
= get_repeating_sequence_dup_machine_mode (builder, mask_bit_mode);
uint64_t full_nelts = builder.full_nelts ().to_constant ();
+ gcc_assert (builder.nelts_per_pattern () == 1
+ || builder.nelts_per_pattern () == 2);
+
+ rtx first
+ = builder.nelts_per_pattern () == 1 ? builder.elt (0) : builder.elt (1);
+
/* Step 1: Broadcast the first pattern. */
- rtx ops[] = {target, force_reg (builder.inner_mode (), builder.elt (0))};
+ rtx ops[] = {target, force_reg (builder.inner_mode (), first)};
expand_broadcast (builder.mode (), ops);
/* Step 2: Merge the rest iteration of pattern. */
for (unsigned int i = 1; i < builder.npatterns (); i++)
@@ -2677,7 +2767,10 @@ expand_vector_init_merge_repeating_sequence (rtx target,
emit_move_insn (mask, gen_lowpart (mask_bit_mode, dup));
/* Step 2-2: Merge pattern according to the mask. */
- rtx ops[] = {target, target, builder.elt (i), mask};
+ unsigned int which = i;
+ if (builder.nelts_per_pattern () == 2)
+ which = 2 * which + 1;
+ rtx ops[] = {target, target, builder.elt (which), mask};
emit_vlmax_insn (code_for_pred_merge_scalar (GET_MODE (target)),
MERGE_OP, ops);
}
@@ -4078,11 +4171,7 @@ shuffle_off_by_one_patterns (struct expand_vec_perm_d *d)
emit_vec_extract (tmp, d->op0, gen_int_mode (nunits - 1, Pmode));
/* Insert the scalar into element 0. */
- unsigned int unspec
- = FLOAT_MODE_P (d->vmode) ? UNSPEC_VFSLIDE1UP : UNSPEC_VSLIDE1UP;
- insn_code icode = code_for_pred_slide (unspec, d->vmode);
- rtx ops[] = {d->target, d->op1, tmp};
- emit_vlmax_insn (icode, BINARY_OP, ops);
+ expand_slide1up (d->vmode, d->op1, tmp);
}
return true;
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr121334.c
b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr121334.c
new file mode 100644
index 00000000000..a2ded48719b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr121334.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv_zvl512b -mabi=lp64d -O3 -fno-vect-cost-model"
} */
+
+char arr[64];
+
+void init ()
+{
+ for (int i = 8; i >= 0; i--)
+ arr[i] = i;
+}
--
2.50.0
