[gcc r14-9781] tree-optimization/114551 - loop splitting and undefined overflow

[Richard Biener via Gcc-cvs]

https://gcc.gnu.org/g:e152177b362143465e2b9d721ea632cae3f13445

commit r14-9781-ge152177b362143465e2b9d721ea632cae3f13445
Author: Richard Biener <rguent...@suse.de>
Date:   Wed Apr 3 14:53:30 2024 +0200

    tree-optimization/114551 - loop splitting and undefined overflow
    
    When loop splitting hoists a guard computation it needs to make sure
    that can be safely evaluated at this place when it was previously
    only conditionally evaluated.  The following fixes this for the
    case of undefined overflow.
    
            PR tree-optimization/114551
            * tree-ssa-loop-split.cc (split_loop): If the guard is
            only conditionally evaluated rewrite computations with
            possibly undefined overflow to unsigned arithmetic.
    
            * gcc.dg/torture/pr114551.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr114551.c | 18 ++++++++++++++++++
 gcc/tree-ssa-loop-split.cc              | 22 ++++++++++++++++++++--
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr114551.c 
b/gcc/testsuite/gcc.dg/torture/pr114551.c
new file mode 100644
index 00000000000..13c15fbc3d9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr114551.c
@@ -0,0 +1,18 @@
+/* { dg-do run } */
+
+int a, b[4], c, d, e, f;
+int main()
+{
+  a--;
+  for (f = 3; f >= 0; f--)
+    {
+      for (e = 0; e < 4; e++)
+       c = 0;
+      for (; c < 4; c++)
+       {
+         d = f && a > 0 && f > (2147483647 - a) ? 0 : b[f];
+         continue;
+       }
+    }
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-split.cc b/gcc/tree-ssa-loop-split.cc
index c0bb1b71d17..a770ea371a2 100644
--- a/gcc/tree-ssa-loop-split.cc
+++ b/gcc/tree-ssa-loop-split.cc
@@ -653,8 +653,26 @@ split_loop (class loop *loop1)
        gimple_seq stmts2;
        border = force_gimple_operand (border, &stmts2, true, NULL_TREE);
        if (stmts2)
-         gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop1),
-                                           stmts2);
+         {
+           /* When the split condition is not always evaluated make sure
+              to rewrite it to defined overflow.  */
+           if (!dominated_by_p (CDI_DOMINATORS, exit1->src, bbs[i]))
+             {
+               gimple_stmt_iterator gsi;
+               gsi = gsi_start (stmts2);
+               while (!gsi_end_p (gsi))
+                 {
+                   gimple *stmt = gsi_stmt (gsi);
+                   if (is_gimple_assign (stmt)
+                       && arith_code_with_undefined_signed_overflow
+                                               (gimple_assign_rhs_code (stmt)))
+                     rewrite_to_defined_overflow (&gsi);
+                   gsi_next (&gsi);
+                 }
+             }
+           gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop1),
+                                             stmts2);
+         }
        tree cond = fold_build2 (guard_code, boolean_type_node,
                                 guard_init, border);
        if (!initial_true)