tree-optimization/91403 - avoid excessive code-generation

The vectorizer, for large permuted grouped loads, generates
inefficient intermediate code (cleaned up only later) that runs
into complexity issues in SCEV analysis and elsewhere.  For the
non-single-element interleaving case we already put a hard limit
in place, this applies the same limit to the missing case.

2021-01-11  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/91403
	* tree-vect-data-refs.c (vect_analyze_group_access_1): Cap
	single-element interleaving group size at 4096 elements.

	* gcc.dg/vect/pr91403.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/vect/pr91403.c b/gcc/testsuite/gcc.dg/vect/pr91403.c
new file mode 100644 (file)
index 0000000..5b9b760
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr91403.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O3" } */
+
+extern int a[][1000000];
+int b;
+void c()
+{
+  for (int d = 2; d <= 9; d++)
+    for (int e = 32; e <= 41; e++)
+      b += a[d][5];
+}

diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index c71ff7378d250e6c42f94179e70926b6950acaa0..97c8577ebe720cf857d811c70eccf60c7655509c 100644 (file)
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -2538,7 +2538,11 @@ vect_analyze_group_access_1 (vec_info *vinfo, dr_vec_info *dr_info)
         size.  */
       if (DR_IS_READ (dr)
          && (dr_step % type_size) == 0
-         && groupsize > 0)
+         && groupsize > 0
+         /* This could be UINT_MAX but as we are generating code in a very
+            inefficient way we have to cap earlier.
+            See PR91403 for example.  */
+         && groupsize <= 4096)
        {
          DR_GROUP_FIRST_ELEMENT (stmt_info) = stmt_info;
          DR_GROUP_SIZE (stmt_info) = groupsize;