[gcc r14-8382] middle-end: fix epilog reductions when vector iters peeled [PR113364]

[gcc r14-8382] middle-end: fix epilog reductions when vector iters peeled [PR113364]

[Tamar Christina]

https://gcc.gnu.org/g:72429448fd16733f876b282bb37a0653049c446d

commit r14-8382-g72429448fd16733f876b282bb37a0653049c446d
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Wed Jan 24 07:37:17 2024 +0000

    middle-end: fix epilog reductions when vector iters peeled [PR113364]
    
    This fixes a bug where vect_create_epilog_for_reduction does not handle the
    case where all exits are early exits.  In this case we should do like induction
    handling code does and not have a main exit.
    
    This shows that some new miscompiles are happening (stage3 is likely miscompiled)
    but that's unrelated to this patch and I'll look at it next.
    
    gcc/ChangeLog:
    
            PR tree-optimization/113364
            * tree-vect-loop.cc (vect_create_epilog_for_reduction): If all exits all
            early exits then we must reduce from the first offset for all of them.
    
    gcc/testsuite/ChangeLog:
    
            PR tree-optimization/113364
            * gcc.dg/vect/vect-early-break_107-pr113364.c: New test.

Diff:
---
 .../gcc.dg/vect/vect-early-break_107-pr113364.c    | 22 ++++++++++++++++++++++
 gcc/tree-vect-loop.cc                              |  3 ++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/vect/vect-early-break_107-pr113364.c b/gcc/testsuite/gcc.dg/vect/vect-early-break_107-pr113364.c
new file mode 100644
index 00000000000..f489265dbfe
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-early-break_107-pr113364.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-add-options vect_early_break } */
+/* { dg-require-effective-target vect_early_break } */
+/* { dg-require-effective-target vect_int } */
+/* { dg-additional-options "-w" } */
+
+typedef const unsigned char *It;
+It DecodeSLEB128(It begin, It end, int *v) {
+  int value = 0;
+  unsigned shift = 0;
+  unsigned char byte;
+  do
+  {
+    if (begin == end)
+      return begin;
+    byte = *(begin++);
+    int slice = byte & 0x7f;
+    value |= slice << shift;
+  } while (byte >= 128);
+  *v = value;
+  return begin;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index fe631252dc2..4da1421c8f0 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -5982,7 +5982,8 @@ vect_create_epilog_for_reduction (loop_vec_info loop_vinfo,
      loop-closed PHI of the inner loop which we remember as
      def for the reduction PHI generation.  */
   bool double_reduc = false;
-  bool main_exit_p = LOOP_VINFO_IV_EXIT (loop_vinfo) == loop_exit;
+  bool main_exit_p = LOOP_VINFO_IV_EXIT (loop_vinfo) == loop_exit
+		     && !LOOP_VINFO_EARLY_BREAKS_VECT_PEELED (loop_vinfo);
   stmt_vec_info rdef_info = stmt_info;
   if (STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def)
     {