scev: Sign extend step in peeled converted IV handling [PR 125291]

For 3 iterations of

    unsigned char flagbits;
    _877 = flagbits_832 + 254;
    _879 = (int) _877;
    # prephitmp_880 = PHI <_879(40), 6(41)>
    _70 = _68 >> prephitmp_880;

The peeled converted IV handling added in r16-3562 incorrectly analyzes
it as [6, 6 + 254, 6 + 254 * 2] instead of [6, 4, 2].  Then VRP uses the
intersect of {6, 560, 514} and {2, 4, 6}, i.e. {6} as the possible value
range, and propagates the constant 6 for _70.

Extend the step (for example, 254 => -2) to fix the issue.

	PR tree-optimization/125291

gcc/

	* tree-scalar-evolution.cc (simplify_peeled_chrec): Sign-extend
	the step for peeled converted IV.

gcc/testsuite/

	* gcc.c-torture/execute/pr125291.c: New test.

diff --git a/gcc/testsuite/gcc.c-torture/execute/pr125291.c b/gcc/testsuite/gcc.c-torture/execute/pr125291.c
new file mode 100644 (file)
index 0000000..073866a
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr125291.c
@@ -0,0 +1,39 @@
+/* PR tree-optimization/125291 */
+
+char buf[1111];
+char *archive_le16dec_filename = buf;
+unsigned int archive_le16dec_end, archive_le16dec_fn_end,
+    archive_le16dec_filename_size, archive_le16dec_offset;
+char archive_le16dec_p[] = { 21, 0x7f };
+
+[[gnu::noipa]]
+void
+archive_le16dec ()
+{
+  archive_le16dec_filename_size = (short)archive_le16dec_filename_size;
+  unsigned char flagbits = 0, flagbyte;
+  archive_le16dec_end = archive_le16dec_filename_size;
+  archive_le16dec_fn_end = archive_le16dec_filename_size * 2;
+  archive_le16dec_filename_size = flagbits = 0;
+  while (archive_le16dec_offset < archive_le16dec_end
+         && archive_le16dec_filename_size < archive_le16dec_fn_end)
+    {
+      if (!flagbits)
+        {
+          flagbyte = archive_le16dec_p[archive_le16dec_offset++];
+          flagbits = 8;
+        }
+      flagbits -= 2;
+      if (!(flagbyte >> flagbits & 3))
+        archive_le16dec_filename_size++;
+    }
+}
+
+int
+main ()
+{
+  archive_le16dec_filename_size = 2;
+  archive_le16dec ();
+  if (archive_le16dec_filename_size != 1)
+    __builtin_trap ();
+}

diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
index f524786f33be6ae46f04c68c796610a8ecfafede..b27037cb02fd92a3185ff778b9e73e150da29e9d 100644 (file)
--- a/gcc/tree-scalar-evolution.cc
+++ b/gcc/tree-scalar-evolution.cc
@@ -1391,10 +1391,19 @@ simplify_peeled_chrec (class loop *loop, tree arg, tree init_cond)
          && wi::to_widest (init_cond) == wi::to_widest (left_before)
          && !scev_probably_wraps_p (NULL_TREE, left_before, right, NULL,
                                     loop, false))
-       return build_polynomial_chrec (loop->num, init_cond,
-                                      chrec_convert (TREE_TYPE (ev),
-                                                     right, NULL,
-                                                     false, NULL_TREE));
+       {
+         tree tp = TREE_TYPE (right);
+
+         /* We need a sign-extension to make things like
+            u8(6, 4, 2) => i32(6, 4, 2), instead of i32(6, 260, 514).  */
+         if (TYPE_UNSIGNED (tp))
+           right = fold_convert (signed_type_for (tp), right);
+
+         return build_polynomial_chrec (loop->num, init_cond,
+                                        chrec_convert (TREE_TYPE (ev),
+                                                       right, NULL,
+                                                       false, NULL_TREE));
+       }
       return chrec_dont_know;
     }