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[V2] Middle-end: Fix bug of induction variable vectorization for RVV

Message ID 20231110122011.3626658-1-juzhe.zhong@rivai.ai
State Accepted
Headers
Series [V2] Middle-end: Fix bug of induction variable vectorization for RVV |

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snail/gcc-patch-check success Github commit url

Commit Message

juzhe.zhong@rivai.ai Nov. 10, 2023, 12:20 p.m. UTC 
  PR: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112438

1. Since SELECT_VL result is not necessary always VF in non-final iteration.

Current GIMPLE IR is wrong:

# vect_vec_iv_.8_22 = PHI <_21(4), { 0, 1, 2, ... }(3)>
...
_35 = .SELECT_VL (ivtmp_33, VF);
_21 = vect_vec_iv_.8_22 + { VF, ... };

E.g. Consider the total iterations N = 6, the VF = 4.
Since SELECT_VL output is defined as not always to be VF in non-final iteration
which needs to depend on hardware implementation.

Suppose we have a RVV CPU core with vsetvl doing even distribution workload optimization.
It may process 3 elements at the 1st iteration and 3 elements at the last iteration.
Then the induction variable here: _21 = vect_vec_iv_.8_22 + { POLY_INT_CST [4, 4], ... }; 
is wrong which is adding VF, which is 4, actually, we didn't process 4 elements.

It should be adding 3 elements which is the result of SELECT_VL.
So, here the correct IR should be:

  _36 = .SELECT_VL (ivtmp_34, VF);
  _22 = (int) _36;
  vect_cst__21 = [vec_duplicate_expr] _22;

2. This issue only happens on non-SLP vectorization single rgroup since:
   
     if (LOOP_VINFO_USING_DECREMENTING_IV_P (loop_vinfo))
    {
      tree iv_type = LOOP_VINFO_RGROUP_IV_TYPE (loop_vinfo);
      if (direct_internal_fn_supported_p (IFN_SELECT_VL, iv_type,
					  OPTIMIZE_FOR_SPEED)
	  && LOOP_VINFO_LENS (loop_vinfo).length () == 1
	  && LOOP_VINFO_LENS (loop_vinfo)[0].factor == 1 && !slp
	  && (!LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
	      || !LOOP_VINFO_VECT_FACTOR (loop_vinfo).is_constant ()))
	LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo) = true;
    }

3. This issue doesn't appears on nested loop no matter LOOP_VINFO_USING_SELECT_VL_P is true or false.

Since:

  # vect_vec_iv_.6_5 = PHI <_19(3), { 0, ... }(5)>
  # vect_diff_15.7_20 = PHI <vect_diff_9.8_22(3), vect_diff_18.5_11(5)>
  _19 = vect_vec_iv_.6_5 + { 1, ... };
  vect_diff_9.8_22 = .COND_LEN_ADD ({ -1, ... }, vect_vec_iv_.6_5, vect_diff_15.7_20, vect_diff_15.7_20, _28, 0);
  ivtmp_1 = ivtmp_4 + 4294967295;
  ....
  <bb 5> [local count: 6549826]:
  # vect_diff_18.5_11 = PHI <vect_diff_9.8_22(4), { 0, ... }(2)>
  # ivtmp_26 = PHI <ivtmp_27(4), 40(2)>
  _28 = .SELECT_VL (ivtmp_26, POLY_INT_CST [4, 4]);
  goto <bb 3>; [100.00%]

Note the induction variable IR: _21 = vect_vec_iv_.8_22 + { POLY_INT_CST [4, 4], ... }; update induction variable
independent on VF (or don't care about how many elements are processed in the iteration).

The update is loop invariant. So it won't be the problem even if LOOP_VINFO_USING_SELECT_VL_P is true.
   
Testing passed, Ok for trunk ?

	PR tree-optimization/112438

gcc/ChangeLog:

	* tree-vect-loop.cc (vectorizable_induction):

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/pr112438.c: New test.

---
 .../gcc.target/riscv/rvv/autovec/pr112438.c   | 33 +++++++++++++++++++
 gcc/tree-vect-loop.cc                         | 30 ++++++++++++++++-
 2 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112438.c
diff mbox series

Patch

diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112438.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112438.c
new file mode 100644
index 00000000000..51f90df38a0
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112438.c
@@ -0,0 +1,33 @@ 
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O3 -fno-vect-cost-model -ffast-math -fdump-tree-optimized-details" } */
+
+void
+foo (int n, int *__restrict in, int *__restrict out)
+{
+  for (int i = 0; i < n; i += 1)
+    {
+      out[i] = in[i] + i;
+    }
+}
+
+void
+foo2 (int n, float * __restrict in, 
+float * __restrict out)
+{
+  for (int i = 0; i < n; i += 1)
+    {
+      out[i] = in[i] + i;
+    }
+}
+
+void
+foo3 (int n, float * __restrict in, 
+float * __restrict out, float x)
+{
+  for (int i = 0; i < n; i += 1)
+    {
+      out[i] = in[i] + i* i;
+    }
+}
+
+/* We don't want to see vect_vec_iv_.21_25 + { POLY_INT_CST [4, 4], ... }.  */
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 8abc1937d74..b152072c969 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -10306,10 +10306,36 @@  vectorizable_induction (loop_vec_info loop_vinfo,
 
 
   /* Create the vector that holds the step of the induction.  */
+  gimple_stmt_iterator *step_iv_si = NULL;
   if (nested_in_vect_loop)
     /* iv_loop is nested in the loop to be vectorized. Generate:
        vec_step = [S, S, S, S]  */
     new_name = step_expr;
+  else if (LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo))
+    {
+      /* When we're using loop_len produced by SELEC_VL, the non-final
+	 iterations are not always processing VF elements.  So vectorize
+	 induction variable instead of
+
+	   _21 = vect_vec_iv_.6_22 + { VF, ... };
+
+	 We should generate:
+
+	   _35 = .SELECT_VL (ivtmp_33, VF);
+	   vect_cst__22 = [vec_duplicate_expr] _35;
+	   _21 = vect_vec_iv_.6_22 + vect_cst__22;  */
+      gcc_assert (!slp_node);
+      gimple_seq seq = NULL;
+      vec_loop_lens *lens = &LOOP_VINFO_LENS (loop_vinfo);
+      tree len = vect_get_loop_len (loop_vinfo, NULL, lens, 1, vectype, 0, 0);
+      expr = force_gimple_operand (fold_convert (TREE_TYPE (step_expr),
+						 unshare_expr (len)),
+				   &seq, true, NULL_TREE);
+      new_name = gimple_build (&seq, MULT_EXPR, TREE_TYPE (step_expr), expr,
+			       step_expr);
+      gsi_insert_seq_before (&si, seq, GSI_SAME_STMT);
+      step_iv_si = &si;
+    }
   else
     {
       /* iv_loop is the loop to be vectorized. Generate:
@@ -10336,7 +10362,7 @@  vectorizable_induction (loop_vec_info loop_vinfo,
 	      || TREE_CODE (new_name) == SSA_NAME);
   new_vec = build_vector_from_val (step_vectype, t);
   vec_step = vect_init_vector (loop_vinfo, stmt_info,
-			       new_vec, step_vectype, NULL);
+			       new_vec, step_vectype, step_iv_si);
 
 
   /* Create the following def-use cycle:
@@ -10382,6 +10408,8 @@  vectorizable_induction (loop_vec_info loop_vinfo,
       gimple_seq seq = NULL;
       /* FORNOW. This restriction should be relaxed.  */
       gcc_assert (!nested_in_vect_loop);
+      /* We expect LOOP_VINFO_USING_SELECT_VL_P to be false if ncopies > 1.  */
+      gcc_assert (!LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo));
 
       /* Create the vector that holds the step of the induction.  */
       if (SCALAR_FLOAT_TYPE_P (TREE_TYPE (step_expr)))