[gcc r14-8952] middle-end: update vector loop upper bounds when early break vect [PR113734]

[Tamar Christina]

https://gcc.gnu.org/g:491e57451df47cda88f658601a92d6d006ae09d7

commit r14-8952-g491e57451df47cda88f658601a92d6d006ae09d7
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Tue Feb 13 11:04:38 2024 +0000

    middle-end: update vector loop upper bounds when early break vect [PR113734]
    
    When doing early break vectorization we should treat the final iteration as
    possibly being partial.  This so that when we calculate the vector loop upper
    bounds we take into account that final iteration could have done some work.
    
    The attached testcase shows that if we don't then cunroll may unroll the loop an
    if the upper bound is wrong we lose a vector iteration.
    
    This is similar to how we adjust the scalar loop bounds for the PEELED case.
    
    gcc/ChangeLog:
    
            PR tree-optimization/113734
            * tree-vect-loop.cc (vect_transform_loop): Treat the final iteration of
            an early break loop as partial.
    
    gcc/testsuite/ChangeLog:
    
            PR tree-optimization/113734
            * gcc.dg/vect/vect-early-break_117-pr113734.c: New test.

Diff:
---
 .../gcc.dg/vect/vect-early-break_117-pr113734.c    | 37 ++++++++++++++++++++++
 gcc/tree-vect-loop.cc                              |  3 +-
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/vect/vect-early-break_117-pr113734.c b/gcc/testsuite/gcc.dg/vect/vect-early-break_117-pr113734.c
new file mode 100644
index 000000000000..36ae09483dfd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-early-break_117-pr113734.c
@@ -0,0 +1,37 @@
+/* { dg-add-options vect_early_break } */
+/* { dg-require-effective-target vect_early_break_hw } */
+/* { dg-require-effective-target vect_int } */
+/* { dg-additional-options "-O3" } */
+
+/* { dg-final { scan-tree-dump "LOOP VECTORIZED" "vect" } } */
+
+#include "tree-vect.h"
+
+#define N 306
+#define NEEDLE 136
+
+int table[N];
+
+__attribute__ ((noipa))
+int foo (int i, unsigned short parse_tables_n)
+{
+  parse_tables_n >>= 9;
+  parse_tables_n += 11;
+  while (i < N && parse_tables_n--)
+    table[i++] = 0;
+
+  return table[NEEDLE];
+}
+
+int main ()
+{
+  check_vect ();
+
+  for (int j = 0; j < N; j++)
+    table[j] = -1;
+
+  if (foo (0, 0xFFFF) != 0)
+    __builtin_abort ();
+
+  return 0;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 04f4b5b6b2fa..367077965fd9 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -12174,7 +12174,8 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
   /* True if the final iteration might not handle a full vector's
      worth of scalar iterations.  */
   bool final_iter_may_be_partial
-    = LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo);
+    = LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo)
+      || LOOP_VINFO_EARLY_BREAKS (loop_vinfo);
   /* The minimum number of iterations performed by the epilogue.  This
      is 1 when peeling for gaps because we always need a final scalar
      iteration.  */