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[PATCH] Fix infinite recursion with div-by-zero (PR middle-end/70992)
- From: Marek Polacek <polacek at redhat dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 18 Jul 2017 18:05:11 +0200
- Subject: [PATCH] Fix infinite recursion with div-by-zero (PR middle-end/70992)
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We ended up in infinite recursion between extract_muldiv_1 and
fold_plusminus_mult_expr, because one turns this expression into the other
and the other does the reverse:
((2147483648 / 0) * 2) + 2 <-> 2 * (2147483648 / 0 + 1)
I tried (unsuccessfully) to fix it in either extract_muldiv_1 or
fold_plusminus_mult_expr, but in the end I went with just turning (x / 0) + A
to x / 0 (and similarly for %), because with that undefined division we can do
anything and this fixes the issue. Any better ideas?
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2017-07-18 Marek Polacek <polacek@redhat.com>
PR middle-end/70992
* fold-const.c (fold_binary_loc): Fold (x / 0) + A to x / 0,
and (x % 0) + A to x % 0.
* gcc.dg/torture/pr70992.c: New test.
* gcc.dg/torture/pr70992-2.c: New test.
diff --git gcc/fold-const.c gcc/fold-const.c
index 1bcbbb58154..9abdc9a8c20 100644
--- gcc/fold-const.c
+++ gcc/fold-const.c
@@ -9387,6 +9387,12 @@ fold_binary_loc (location_t loc,
TREE_TYPE (arg0), arg0,
cst0));
}
+ /* Adding anything to a division-by-zero makes no sense and
+ can confuse extract_muldiv and fold_plusminus_mult_expr. */
+ else if ((TREE_CODE (arg0) == TRUNC_DIV_EXPR
+ || TREE_CODE (arg0) == TRUNC_MOD_EXPR)
+ && integer_zerop (TREE_OPERAND (arg0, 1)))
+ return fold_convert_loc (loc, type, arg0);
}
/* Handle (A1 * C1) + (A2 * C2) with A1, A2 or C1, C2 being the same or
diff --git gcc/testsuite/gcc.dg/torture/pr70992-2.c gcc/testsuite/gcc.dg/torture/pr70992-2.c
index e69de29bb2d..c5d2c5f2683 100644
--- gcc/testsuite/gcc.dg/torture/pr70992-2.c
+++ gcc/testsuite/gcc.dg/torture/pr70992-2.c
@@ -0,0 +1,9 @@
+/* PR middle-end/70992 */
+/* { dg-do compile } */
+
+unsigned int *od;
+int
+fn (void)
+{
+ return (0 % 0 + 1) * *od * 2; /* { dg-warning "division by zero" } */
+}
diff --git gcc/testsuite/gcc.dg/torture/pr70992.c gcc/testsuite/gcc.dg/torture/pr70992.c
index e69de29bb2d..56728e09d1b 100644
--- gcc/testsuite/gcc.dg/torture/pr70992.c
+++ gcc/testsuite/gcc.dg/torture/pr70992.c
@@ -0,0 +1,41 @@
+/* PR middle-end/70992 */
+/* { dg-do compile } */
+
+typedef unsigned int uint32_t;
+typedef int int32_t;
+
+uint32_t
+fn (uint32_t so)
+{
+ return (so + so) * (0x80000000 / 0 + 1); /* { dg-warning "division by zero" } */
+}
+
+uint32_t
+fn5 (uint32_t so)
+{
+ return (0x80000000 / 0 + 1) * (so + so); /* { dg-warning "division by zero" } */
+}
+
+uint32_t
+fn6 (uint32_t so)
+{
+ return (0x80000000 / 0 - 1) * (so + so); /* { dg-warning "division by zero" } */
+}
+
+uint32_t
+fn2 (uint32_t so)
+{
+ return (so + so) * (0x80000000 / 0 - 1); /* { dg-warning "division by zero" } */
+}
+
+int32_t
+fn3 (int32_t so)
+{
+ return (so + so) * (0x80000000 / 0 + 1); /* { dg-warning "division by zero" } */
+}
+
+int32_t
+fn4 (int32_t so)
+{
+ return (so + so) * (0x80000000 / 0 - 1); /* { dg-warning "division by zero" } */
+}
Marek