[gcc r14-7036] middle-end: rejects loops with nonlinear inductions and early breaks [PR113163]

[Tamar Christina]

https://gcc.gnu.org/g:cbf569486b2decbde0308f9f4d0f0837e4cfefd9

commit r14-7036-gcbf569486b2decbde0308f9f4d0f0837e4cfefd9
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Tue Jan 9 11:16:16 2024 +0000

    middle-end: rejects loops with nonlinear inductions and early breaks [PR113163]
    
    We can't support nonlinear inductions other than neg when vectorizing
    early breaks and iteration count is known.
    
    For early break we currently require a peeled epilog but in these cases
    we can't compute the remaining values.
    
    gcc/ChangeLog:
    
            PR middle-end/113163
            * tree-vect-loop-manip.cc (vect_can_peel_nonlinear_iv_p):
            Reject non-linear inductions that aren't supported.
    
    gcc/testsuite/ChangeLog:
    
            PR middle-end/113163
            * gcc.target/gcn/pr113163.c: New test.

Diff:
---
 gcc/testsuite/gcc.target/gcn/pr113163.c | 30 ++++++++++++++++++++++++++++++
 gcc/tree-vect-loop-manip.cc             | 19 +++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/gcc/testsuite/gcc.target/gcn/pr113163.c b/gcc/testsuite/gcc.target/gcn/pr113163.c
new file mode 100644
index 00000000000..99b0fdbaf3a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/gcn/pr113163.c
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O2 -ftree-vectorize" } */ 
+
+struct _reent { union { struct { char _l64a_buf[8]; } _reent; } _new; };
+static const char R64_ARRAY[] = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+char *
+_l64a_r (struct _reent *rptr,
+     long value)
+{
+  char *ptr;
+  char *result;
+  int i, index;
+  unsigned long tmp = (unsigned long)value & 0xffffffff;
+  result = 
+          ((
+          rptr
+          )->_new._reent._l64a_buf)
+                               ;
+  ptr = result;
+  for (i = 0; i < 6; ++i)
+    {
+      if (tmp == 0)
+ {
+   *ptr = '\0';
+   break;
+ }
+      *ptr++ = R64_ARRAY[index];
+      tmp >>= 6;
+    }
+}
diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 927f76a0947..2313d26338d 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -2063,6 +2063,25 @@ vect_can_peel_nonlinear_iv_p (loop_vec_info loop_vinfo,
       return false;
     }
 
+  /* We can't support partial vectors and early breaks with an induction
+     type other than add or neg since we require the epilog and can't
+     perform the peeling.  The below condition mirrors that of
+     vect_gen_vector_loop_niters  where niters_vector_mult_vf_var then sets
+     step_vector to VF rather than 1.  This is what creates the nonlinear
+     IV.  PR113163.  */
+  if (LOOP_VINFO_EARLY_BREAKS (loop_vinfo)
+      && LOOP_VINFO_VECT_FACTOR (loop_vinfo).is_constant ()
+      && LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo)
+      && induction_type != vect_step_op_neg)
+    {
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			 "Peeling for epilogue is not supported"
+			 " for nonlinear induction except neg"
+			 " when VF is known and early breaks.\n");
+      return false;
+    }
+
   return true;
 }