[PATCH] Fix PR86945

[Richard Biener]

The following fixes PR86945, single-case switch conversion to
range check using signed arithmetic that can overflow.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2018-08-22  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/86945
        * tree-cfg.c (generate_range_test): Use unsigned arithmetic.

        * gcc.dg/torture/pr86945.c: New testcase.

Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c      (revision 263705)
+++ gcc/tree-cfg.c      (working copy)
@@ -9131,20 +9131,16 @@ generate_range_test (basic_block bb, tre
   tree type = TREE_TYPE (index);
   tree utype = unsigned_type_for (type);
 
-  low = fold_convert (type, low);
-  high = fold_convert (type, high);
+  low = fold_convert (utype, low);
+  high = fold_convert (utype, high);
 
-  tree tmp = make_ssa_name (type);
-  gassign *sub1
-    = gimple_build_assign (tmp, MINUS_EXPR, index, low);
+  gimple_seq seq = NULL;
+  index = gimple_convert (&seq, utype, index);
+  *lhs = gimple_build (&seq, MINUS_EXPR, utype, index, low);
+  *rhs = const_binop (MINUS_EXPR, utype, high, low);
 
-  *lhs = make_ssa_name (utype);
-  gassign *a = gimple_build_assign (*lhs, NOP_EXPR, tmp);
-
-  *rhs = fold_build2 (MINUS_EXPR, utype, high, low);
   gimple_stmt_iterator gsi = gsi_last_bb (bb);
-  gsi_insert_before (&gsi, sub1, GSI_SAME_STMT);
-  gsi_insert_before (&gsi, a, GSI_SAME_STMT);
+  gsi_insert_seq_before (&gsi, seq, GSI_SAME_STMT);
 }
 
 /* Emit return warnings.  */
Index: gcc/testsuite/gcc.dg/torture/pr86945.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr86945.c      (nonexistent)
+++ gcc/testsuite/gcc.dg/torture/pr86945.c      (working copy)
@@ -0,0 +1,18 @@
+/* { dg-do run } */
+
+void __attribute__((noinline,noipa))
+foo(int id)
+{
+  switch (id)
+    {
+    case (-__INT_MAX__ - 1)...-1:
+      __builtin_abort ();
+    default:;
+    }
+}
+
+int main()
+{
+  foo(1);
+  return 0;
+}