The following testcase ICEd because we were trying to negate
"-9223372036854775808", which results in UB, since it's LLONG_MAX + 1.
Then we got a SIGFPE on
-LLONG_MIN / -1
So fixed by doing the arithmetics on trees, and in case we got
an overflow, we bail out.
The hunk
probability = (double) REG_BR_PROB_BASE * compare_count / loop_count;
in there should be probably handled in the same way. But I'll handle
that separately.
In the first hunk, I did s/int/HOST_WIDE_INT/, because HWI is what
tree_low_cst returns. For why that could be a problem, see the
Jakub's comment in the PR.
Regtested/bootstrapped on x86_64-linux, ok for trunk?
2013-02-28 Marek Polacek <pola...@redhat.com>
PR tree-optimization/56478
* predict.c (is_comparison_with_loop_invariant_p): Change the
type of step to HOST_WIDE_INT.
(predict_iv_comparison): Do the computation on trees, return
in case of an overflow.
* gcc.dg/torture/pr56478.c: New test.
--- gcc/predict.c.mp 2013-02-28 17:26:47.950247877 +0100
+++ gcc/predict.c 2013-02-28 17:26:56.855275792 +0100
@@ -1034,7 +1034,7 @@ is_comparison_with_loop_invariant_p (gim
tree op0, op1, bound, base;
affine_iv iv0, iv1;
enum tree_code code;
- int step;
+ HOST_WIDE_INT step;
code = gimple_cond_code (stmt);
*loop_invariant = NULL;
@@ -1224,11 +1224,29 @@ predict_iv_comparison (struct loop *loop
&& host_integerp (compare_base, 0))
{
int probability;
+ tree step_var, loop_count_var;
HOST_WIDE_INT compare_count;
HOST_WIDE_INT loop_bound = tree_low_cst (loop_bound_var, 0);
HOST_WIDE_INT compare_bound = tree_low_cst (compare_var, 0);
HOST_WIDE_INT base = tree_low_cst (compare_base, 0);
- HOST_WIDE_INT loop_count = (loop_bound - base) / compare_step;
+
+ /* We want to do the arithmetics on trees (and punt in
+ case of an overflow). */
+ step_var = build_int_cst (NULL_TREE, compare_step);
+ gcc_assert (TREE_CODE (step_var) == INTEGER_CST);
+
+ /* Compute (loop_bound - base) / compare_step. */
+ loop_count_var
+ = int_const_binop (TRUNC_DIV_EXPR,
+ int_const_binop (MINUS_EXPR,
+ loop_bound_var,
+ compare_base),
+ step_var);
+
+ if (TREE_OVERFLOW_P (loop_count_var))
+ return;
+
+ HOST_WIDE_INT loop_count = tree_low_cst (loop_count_var, 0);
if ((compare_step > 0)
^ (compare_code == LT_EXPR || compare_code == LE_EXPR))
--- gcc/testsuite/gcc.dg/torture/pr56478.c.mp 2013-02-28 17:32:26.430308968
+0100
+++ gcc/testsuite/gcc.dg/torture/pr56478.c 2013-02-28 18:15:41.641379179
+0100
@@ -0,0 +1,12 @@
+/* PR tree-optimization/56478 */
+/* { dg-do compile } */
+
+int a;
+
+void
+foo ()
+{
+ int b;
+ for (b = 0;; b++)
+ a = 0 < -__LONG_LONG_MAX__ - 1 - b ? : 0;
+}
Marek
