Checking undefined_p before using the vr

For pattern "(X + C) / N": "div (plus@3 @0 INTEGER_CST@1) INTEGER_CST@2)",
Even if "X" has value-range and "X + C" does not overflow, "@3" may still
be undefined. Like below example:

_3 = _2 + -5;
if (0 != 0)
  goto <bb 3>; [34.00%]
else
  goto <bb 4>; [66.00%]
;;  succ:       3
;;              4

;; basic block 3, loop depth 0
;;  pred:       2
_5 = _3 / 5;
;;  succ:       4

The whole pattern "(_2 + -5 ) / 5" is in "bb 3", but "bb 3" would be
unreachable (because "if (0 != 0)" is always false).
And "get_range_query (cfun)->range_of_expr (vr3, @3)" is checked in
"bb 3", "range_of_expr" gets an "undefined vr3". Where "@3" is "_5".

So, before using "vr3", it would be safe to check "!vr3.undefined_p ()".

	PR tree-optimization/111303

gcc/ChangeLog:

	* match.pd ((X - N * M) / N): Add undefined_p checking.
	((X + N * M) / N): Likewise.
	((X + C) div_rshift N): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr111303.c: New test.

diff --git a/gcc/match.pd b/gcc/match.pd
index 39c7ea1088f25538ed8bd26ee89711566141a71f..693638f8ca03dd63f760de7facc229680130495b 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -975,6 +975,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
        /* "X+(N*M)" doesn't overflow.  */
        && range_op_handler (PLUS_EXPR).overflow_free_p (vr0, vr3)
        && get_range_query (cfun)->range_of_expr (vr4, @4)
+       && !vr4.undefined_p ()
        /* "X+N*M" is not with opposite sign as "X".  */
        && (TYPE_UNSIGNED (type)
           || (vr0.nonnegative_p () && vr4.nonnegative_p ())
@@ -995,6 +996,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
        /* "X - (N*M)" doesn't overflow.  */
        && range_op_handler (MINUS_EXPR).overflow_free_p (vr0, vr3)
        && get_range_query (cfun)->range_of_expr (vr4, @4)
+       && !vr4.undefined_p ()
        /* "X-N*M" is not with opposite sign as "X".  */
        && (TYPE_UNSIGNED (type)
           || (vr0.nonnegative_p () && vr4.nonnegative_p ())
@@ -1025,6 +1027,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
          /* "X+C" doesn't overflow.  */
          && range_op_handler (PLUS_EXPR).overflow_free_p (vr0, vr1)
          && get_range_query (cfun)->range_of_expr (vr3, @3)
+         && !vr3.undefined_p ()
          /* "X+C" and "X" are not of opposite sign.  */
          && (TYPE_UNSIGNED (type)
              || (vr0.nonnegative_p () && vr3.nonnegative_p ())

diff --git a/gcc/testsuite/gcc.dg/pr111303.c b/gcc/testsuite/gcc.dg/pr111303.c
new file mode 100644 (file)
index 0000000..eaabe55
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr111303.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+/* Make sure no ICE. */
+unsigned char a;
+int b(int c) {
+  if (c >= 5000)
+    return c / 5;
+}
+void d() { b(a - 5); }
+int main() {}