[PATCH] tree-optimization/114551 - loop splitting and undefined overflow

[Richard Biener <rguenther@suse.de>]

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.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

	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.
---
 gcc/testsuite/gcc.dg/torture/pr114551.c | 18 ++++++++++++++++++
 gcc/tree-ssa-loop-split.cc              | 22 ++++++++++++++++++++--
 2 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr114551.c

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)
-- 
2.35.3