diff mbox series

[v2] RISC-V: Bugfix for the const vector in single steps

Message ID 20231220065606.2695737-1-pan2.li@intel.com
State New
Headers show
Series [v2] RISC-V: Bugfix for the const vector in single steps | expand

Commit Message

Li, Pan2 Dec. 20, 2023, 6:56 a.m. UTC 
From: Pan Li <pan2.li@intel.com>

This patch would like to fix the below execution failure.

FAIL: gcc.dg/vect/pr92420.c -flto -ffat-lto-objects execution test

The will be one single step const vector like { -4, 4, -3, 5, -2, 6, -1, 7, ...}.
For such const vector generation with single step, we will generate vid
+ diff here. For example as below, given npatterns = 4.

v1= {3, 2, 1, 0, 7, 6, 5, 4, 11, 10, 9, 8... }
v2 (diff) = {3 - 0, 2 - 1, 1 - 2, 0 - 3, 7 - 4, 6 - 5, 5 - 6, 4 - 7...}
          = {3, 1, -1, 3, 3, 1, -1, 3 ...}
v1 = vd + vid.

Unfortunately, that cannot work well for { -4, 4, -3, 5, -2, 6, -1, 7, ...}
because it has one implicit requirement for the diff. Aka, the diff
sequence in npattern are repeated. For example the v2 (diff) as above.

The diff between { -4, 4, -3, 5, -2, 6, -1, 7, ...} and vid are not
npattern size repeated and then we have wrong code here. We implement
one new code gen the sequence like { -4, 4, -3, 5, -2, 6, -1, 7, ...}.

The below tests are passed for this patch.

* The RV64 regression test with rv64gcv configuration.
* The run test gcc.dg/vect/pr92420.c for below configurations.

riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8/--param=riscv-autovec-preference=fixed-vlmax

gcc/ChangeLog:

	* config/riscv/riscv-v.cc (expand_const_vector): Add restriction
	for the vid-diff code gen and implement general one.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/bug-7.c: New test.

Signed-off-by: Pan Li <pan2.li@intel.com>
---
 gcc/config/riscv/riscv-v.cc                   | 84 +++++++++++++++----
 .../gcc.target/riscv/rvv/autovec/bug-7.c      | 61 ++++++++++++++
 2 files changed, 130 insertions(+), 15 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/bug-7.c

Comments

juzhe.zhong@rivai.ai Dec. 20, 2023, 6:58 a.m. UTC | #1 
+	      bool diff_seq_repeated_p = true;
+
+	      for (unsigned i = 0; i < v.npatterns (); i++)
+		{
+		  poly_int64 diff_0 = rtx_to_poly_int64 (builder.elt (i)) - i;
+		  poly_int64 diff_1 = rtx_to_poly_int64 (
+		    builder.elt (v.npatterns () + i)) - v.npatterns () - i;
+
+		  if (maybe_ne (diff_0, diff_1))
+		    {
+		      diff_seq_repeated_p = false;
+		      break;
+		    }
+		}

This code should be wrapped as a helper function inside class rvv_builder


juzhe.zhong@rivai.ai
 
From: pan2.li
Date: 2023-12-20 14:56
To: gcc-patches
CC: juzhe.zhong; pan2.li; yanzhang.wang; kito.cheng; jeffreyalaw
Subject: [PATCH v2] RISC-V: Bugfix for the const vector in single steps
From: Pan Li <pan2.li@intel.com>
 
This patch would like to fix the below execution failure.
 
FAIL: gcc.dg/vect/pr92420.c -flto -ffat-lto-objects execution test
 
The will be one single step const vector like { -4, 4, -3, 5, -2, 6, -1, 7, ...}.
For such const vector generation with single step, we will generate vid
+ diff here. For example as below, given npatterns = 4.
 
v1= {3, 2, 1, 0, 7, 6, 5, 4, 11, 10, 9, 8... }
v2 (diff) = {3 - 0, 2 - 1, 1 - 2, 0 - 3, 7 - 4, 6 - 5, 5 - 6, 4 - 7...}
          = {3, 1, -1, 3, 3, 1, -1, 3 ...}
v1 = vd + vid.
 
Unfortunately, that cannot work well for { -4, 4, -3, 5, -2, 6, -1, 7, ...}
because it has one implicit requirement for the diff. Aka, the diff
sequence in npattern are repeated. For example the v2 (diff) as above.
 
The diff between { -4, 4, -3, 5, -2, 6, -1, 7, ...} and vid are not
npattern size repeated and then we have wrong code here. We implement
one new code gen the sequence like { -4, 4, -3, 5, -2, 6, -1, 7, ...}.
 
The below tests are passed for this patch.
 
* The RV64 regression test with rv64gcv configuration.
* The run test gcc.dg/vect/pr92420.c for below configurations.
 
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8
riscv-sim/-march=rv64gcv/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8
riscv-sim/-march=rv64gcv_zvl256b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m1/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m2/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m4/--param=riscv-autovec-preference=fixed-vlmax
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8
riscv-sim/-march=rv64gcv_zvl512b/-mabi=lp64d/-mcmodel=medlow/--param=riscv-autovec-lmul=m8/--param=riscv-autovec-preference=fixed-vlmax
 
gcc/ChangeLog:
 
* config/riscv/riscv-v.cc (expand_const_vector): Add restriction
for the vid-diff code gen and implement general one.
 
gcc/testsuite/ChangeLog:
 
* gcc.target/riscv/rvv/autovec/bug-7.c: New test.
 
Signed-off-by: Pan Li <pan2.li@intel.com>
---
gcc/config/riscv/riscv-v.cc                   | 84 +++++++++++++++----
.../gcc.target/riscv/rvv/autovec/bug-7.c      | 61 ++++++++++++++
2 files changed, 130 insertions(+), 15 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/bug-7.c
 
diff --git a/gcc/config/riscv/riscv-v.cc b/gcc/config/riscv/riscv-v.cc
index 486f5deb296..5a5899e85ae 100644
--- a/gcc/config/riscv/riscv-v.cc
+++ b/gcc/config/riscv/riscv-v.cc
@@ -1257,24 +1257,78 @@ expand_const_vector (rtx target, rtx src)
  else
    {
      /* Generate the variable-length vector following this rule:
- { a, b, a, b, a + step, b + step, a + step*2, b + step*2, ...}
-    E.g. { 3, 2, 1, 0, 7, 6, 5, 4, ... } */
-       /* Step 2: Generate diff = TARGET - VID:
- { 3-0, 2-1, 1-2, 0-3, 7-4, 6-5, 5-6, 4-7, ... }*/
+ { a, b, a + step, b + step, a + step*2, b + step*2, ... }  */
      rvv_builder v (builder.mode (), builder.npatterns (), 1);
-       for (unsigned int i = 0; i < v.npatterns (); ++i)
+       bool diff_seq_repeated_p = true;
+
+       for (unsigned i = 0; i < v.npatterns (); i++)
+ {
+   poly_int64 diff_0 = rtx_to_poly_int64 (builder.elt (i)) - i;
+   poly_int64 diff_1 = rtx_to_poly_int64 (
+     builder.elt (v.npatterns () + i)) - v.npatterns () - i;
+
+   if (maybe_ne (diff_0, diff_1))
+     {
+       diff_seq_repeated_p = false;
+       break;
+     }
+ }
+
+       if (diff_seq_repeated_p)
+ {
+   /* Case 1: For example as below:
+      {3, 2, 1, 0, 7, 6, 5, 4, 11, 10, 9, 8... }
+      We have 3 - 0 = 3 equals 7 - 4 = 3, the sequence is
+      repeated as below after minus vid.
+      {3, 1, -1, -3, 3, 1, -1, -3...}
+      Then we can simplify the diff code gen to at most
+      npatterns().  */
+
+   /* Step 1: Generate diff = TARGET - VID.  */
+   for (unsigned int i = 0; i < v.npatterns (); ++i)
+     {
+      poly_int64 diff = rtx_to_poly_int64 (builder.elt (i)) - i;
+      v.quick_push (gen_int_mode (diff, v.inner_mode ()));
+     }
+
+   /* Step 2: Generate result = VID + diff.  */
+   rtx vec = v.build ();
+   rtx add_ops[] = {target, vid, vec};
+   emit_vlmax_insn (code_for_pred (PLUS, builder.mode ()),
+    BINARY_OP, add_ops);
+ }
+       else
{
-   /* Calculate the diff between the target sequence and
-      vid sequence.  The elt (i) can be either const_int or
-      const_poly_int. */
-   poly_int64 diff = rtx_to_poly_int64 (builder.elt (i)) - i;
-   v.quick_push (gen_int_mode (diff, v.inner_mode ()));
+   /* Case 2: For example as below:
+      { -4, 4, -4 + 1, 4 + 1, -4 + 2, 4 + 2, -4 + 3, 4 + 3, ... }
+    */
+
+   /* Step 1: Generate { a, b, a, b, ... }  */
+   for (unsigned int i = 0; i < v.npatterns (); ++i)
+     v.quick_push (builder.elt (i));
+   rtx new_base = v.build ();
+
+   /* Step 2: Generate tmp = VID >> LOG2 (NPATTERNS).  */
+   rtx shift_count
+     = gen_int_mode (exact_log2 (builder.npatterns ()),
+     builder.inner_mode ());
+   rtx tmp = expand_simple_binop (builder.mode (), LSHIFTRT,
+ vid, shift_count, NULL_RTX,
+ false, OPTAB_DIRECT);
+
+   /* Step 3: Generate tmp2 = tmp * step.  */
+   rtx tmp2 = gen_reg_rtx (builder.mode ());
+   rtx step
+     = simplify_binary_operation (MINUS, builder.inner_mode (),
+ builder.elt (v.npatterns()),
+ builder.elt (0));
+   expand_vec_series (tmp2, const0_rtx, step, tmp);
+
+   /* Step 4: Generate target = tmp2 + new_base.  */
+   rtx add_ops[] = {target, tmp2, new_base};
+   emit_vlmax_insn (code_for_pred (PLUS, builder.mode ()),
+    BINARY_OP, add_ops);
}
-       /* Step 2: Generate result = VID + diff.  */
-       rtx vec = v.build ();
-       rtx add_ops[] = {target, vid, vec};
-       emit_vlmax_insn (code_for_pred (PLUS, builder.mode ()),
- BINARY_OP, add_ops);
    }
}
       else if (builder.interleaved_stepped_npatterns_p ())
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/bug-7.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/bug-7.c
new file mode 100644
index 00000000000..9acac391f65
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/bug-7.c
@@ -0,0 +1,61 @@
+/* { dg-do run { target { riscv_v } } } */
+/* { dg-additional-options "-std=c99 -O3 -ftree-vectorize -fno-vect-cost-model -ffast-math" } */
+
+#define N 4
+struct C { int l, r; };
+struct C a[N], b[N], c[N];
+struct C a1[N], b1[N], c1[N];
+
+void __attribute__((noinline))
+init_data_vec (struct C * __restrict a, struct C * __restrict b,
+        struct C * __restrict c)
+{
+  int i;
+
+  for (i = 0; i < N; ++i)
+    {
+      a[i].l = N - i;
+      a[i].r = i - N;
+
+      b[i].l = i - N;
+      b[i].r = i + N;
+
+      c[i].l = -1 - i;
+      c[i].r = 2 * N - 1 - i;
+    }
+}
+
+int
+main ()
+{
+  int i;
+
+  init_data_vec (a, b, c);
+
+#pragma GCC novector
+  for (i = 0; i < N; ++i)
+    {
+      a1[i].l = N - i;
+      a1[i].r = i - N;
+
+      b1[i].l = i - N;
+      b1[i].r = i + N;
+
+      c1[i].l = -1 - i;
+      c1[i].r = 2 * N - 1 - i;
+    }
+
+  for (i = 0; i < N; i++)
+    {
+      if (a[i].l != a1[i].l || a[i].r != a1[i].r)
+ __builtin_abort ();
+
+      if (b[i].l != b1[i].l || b[i].r != b1[i].r)
+ __builtin_abort ();
+
+      if (c[i].l != c1[i].l || c[i].r != c1[i].r)
+ __builtin_abort ();
+    }
+
+  return 0;
+}
Li, Pan2 Dec. 20, 2023, 7:01 a.m. UTC | #2 
Thanks for reviewing, sure and will send V3 for it.

Pan

From: juzhe.zhong@rivai.ai <juzhe.zhong@rivai.ai>
Sent: Wednesday, December 20, 2023 2:59 PM
To: Li, Pan2 <pan2.li@intel.com>; gcc-patches <gcc-patches@gcc.gnu.org>
Cc: Li, Pan2 <pan2.li@intel.com>; Wang, Yanzhang <yanzhang.wang@intel.com>; kito.cheng <kito.cheng@gmail.com>; jeffreyalaw <jeffreyalaw@gmail.com>
Subject: Re: [PATCH v2] RISC-V: Bugfix for the const vector in single steps


+             bool diff_seq_repeated_p = true;

+

+             for (unsigned i = 0; i < v.npatterns (); i++)

+              {

+                poly_int64 diff_0 = rtx_to_poly_int64 (builder.elt (i)) - i;

+                poly_int64 diff_1 = rtx_to_poly_int64 (

+                  builder.elt (v.npatterns () + i)) - v.npatterns () - i;

+

+                if (maybe_ne (diff_0, diff_1))

+                  {

+                    diff_seq_repeated_p = false;

+                    break;

+                  }

+              }

This code should be wrapped as a helper function inside class rvv_builder
diff mbox series

Patch

diff --git a/gcc/config/riscv/riscv-v.cc b/gcc/config/riscv/riscv-v.cc
index 486f5deb296..5a5899e85ae 100644
--- a/gcc/config/riscv/riscv-v.cc
+++ b/gcc/config/riscv/riscv-v.cc
@@ -1257,24 +1257,78 @@  expand_const_vector (rtx target, rtx src)
 	  else
 	    {
 	      /* Generate the variable-length vector following this rule:
-		 { a, b, a, b, a + step, b + step, a + step*2, b + step*2, ...}
-		   E.g. { 3, 2, 1, 0, 7, 6, 5, 4, ... } */
-	      /* Step 2: Generate diff = TARGET - VID:
-		 { 3-0, 2-1, 1-2, 0-3, 7-4, 6-5, 5-6, 4-7, ... }*/
+		{ a, b, a + step, b + step, a + step*2, b + step*2, ... }  */
 	      rvv_builder v (builder.mode (), builder.npatterns (), 1);
-	      for (unsigned int i = 0; i < v.npatterns (); ++i)
+	      bool diff_seq_repeated_p = true;
+
+	      for (unsigned i = 0; i < v.npatterns (); i++)
+		{
+		  poly_int64 diff_0 = rtx_to_poly_int64 (builder.elt (i)) - i;
+		  poly_int64 diff_1 = rtx_to_poly_int64 (
+		    builder.elt (v.npatterns () + i)) - v.npatterns () - i;
+
+		  if (maybe_ne (diff_0, diff_1))
+		    {
+		      diff_seq_repeated_p = false;
+		      break;
+		    }
+		}
+
+	      if (diff_seq_repeated_p)
+		{
+		  /* Case 1: For example as below:
+		     {3, 2, 1, 0, 7, 6, 5, 4, 11, 10, 9, 8... }
+		     We have 3 - 0 = 3 equals 7 - 4 = 3, the sequence is
+		     repeated as below after minus vid.
+		     {3, 1, -1, -3, 3, 1, -1, -3...}
+		     Then we can simplify the diff code gen to at most
+		     npatterns().  */
+
+		  /* Step 1: Generate diff = TARGET - VID.  */
+		  for (unsigned int i = 0; i < v.npatterns (); ++i)
+		    {
+		     poly_int64 diff = rtx_to_poly_int64 (builder.elt (i)) - i;
+		     v.quick_push (gen_int_mode (diff, v.inner_mode ()));
+		    }
+
+		  /* Step 2: Generate result = VID + diff.  */
+		  rtx vec = v.build ();
+		  rtx add_ops[] = {target, vid, vec};
+		  emit_vlmax_insn (code_for_pred (PLUS, builder.mode ()),
+				   BINARY_OP, add_ops);
+		}
+	      else
 		{
-		  /* Calculate the diff between the target sequence and
-		     vid sequence.  The elt (i) can be either const_int or
-		     const_poly_int. */
-		  poly_int64 diff = rtx_to_poly_int64 (builder.elt (i)) - i;
-		  v.quick_push (gen_int_mode (diff, v.inner_mode ()));
+		  /* Case 2: For example as below:
+		     { -4, 4, -4 + 1, 4 + 1, -4 + 2, 4 + 2, -4 + 3, 4 + 3, ... }
+		   */
+
+		  /* Step 1: Generate { a, b, a, b, ... }  */
+		  for (unsigned int i = 0; i < v.npatterns (); ++i)
+		    v.quick_push (builder.elt (i));
+		  rtx new_base = v.build ();
+
+		  /* Step 2: Generate tmp = VID >> LOG2 (NPATTERNS).  */
+		  rtx shift_count
+		    = gen_int_mode (exact_log2 (builder.npatterns ()),
+				    builder.inner_mode ());
+		  rtx tmp = expand_simple_binop (builder.mode (), LSHIFTRT,
+						 vid, shift_count, NULL_RTX,
+						 false, OPTAB_DIRECT);
+
+		  /* Step 3: Generate tmp2 = tmp * step.  */
+		  rtx tmp2 = gen_reg_rtx (builder.mode ());
+		  rtx step
+		    = simplify_binary_operation (MINUS, builder.inner_mode (),
+						 builder.elt (v.npatterns()),
+						 builder.elt (0));
+		  expand_vec_series (tmp2, const0_rtx, step, tmp);
+
+		  /* Step 4: Generate target = tmp2 + new_base.  */
+		  rtx add_ops[] = {target, tmp2, new_base};
+		  emit_vlmax_insn (code_for_pred (PLUS, builder.mode ()),
+				   BINARY_OP, add_ops);
 		}
-	      /* Step 2: Generate result = VID + diff.  */
-	      rtx vec = v.build ();
-	      rtx add_ops[] = {target, vid, vec};
-	      emit_vlmax_insn (code_for_pred (PLUS, builder.mode ()),
-				BINARY_OP, add_ops);
 	    }
 	}
       else if (builder.interleaved_stepped_npatterns_p ())
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/bug-7.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/bug-7.c
new file mode 100644
index 00000000000..9acac391f65
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/bug-7.c
@@ -0,0 +1,61 @@ 
+/* { dg-do run { target { riscv_v } } } */
+/* { dg-additional-options "-std=c99 -O3 -ftree-vectorize -fno-vect-cost-model -ffast-math" } */
+
+#define N 4
+struct C { int l, r; };
+struct C a[N], b[N], c[N];
+struct C a1[N], b1[N], c1[N];
+
+void __attribute__((noinline))
+init_data_vec (struct C * __restrict a, struct C * __restrict b,
+	       struct C * __restrict c)
+{
+  int i;
+
+  for (i = 0; i < N; ++i)
+    {
+      a[i].l = N - i;
+      a[i].r = i - N;
+
+      b[i].l = i - N;
+      b[i].r = i + N;
+
+      c[i].l = -1 - i;
+      c[i].r = 2 * N - 1 - i;
+    }
+}
+
+int
+main ()
+{
+  int i;
+
+  init_data_vec (a, b, c);
+
+#pragma GCC novector
+  for (i = 0; i < N; ++i)
+    {
+      a1[i].l = N - i;
+      a1[i].r = i - N;
+
+      b1[i].l = i - N;
+      b1[i].r = i + N;
+
+      c1[i].l = -1 - i;
+      c1[i].r = 2 * N - 1 - i;
+    }
+
+  for (i = 0; i < N; i++)
+    {
+      if (a[i].l != a1[i].l || a[i].r != a1[i].r)
+	__builtin_abort ();
+
+      if (b[i].l != b1[i].l || b[i].r != b1[i].r)
+	__builtin_abort ();
+
+      if (c[i].l != c1[i].l || c[i].r != c1[i].r)
+	__builtin_abort ();
+    }
+
+  return 0;
+}