Two fixes for UB when handling very large offsets. The calculation in
force_int_to_mode would have been correct if signed integers used modulo
arithmetic, so just switch to unsigned types. The calculation in
rtx_addr_can_trap_p_1 didn't handle overflow properly, so switch to
known_subrange_p instead (which is supposed to handle all cases).
Tested with bootstrap-ubsan on aarch64-linux-gnu and x86_64-linux-gnu.
OK to install?
Richard
2019-04-18 Richard Sandiford <richard.sandif...@arm.com>
gcc/
PR middle-end/85164
* combine.c (force_int_to_mode): Cast the argument rather than
the result of known_alignment.
* rtlanal.c (rtx_addr_can_trap_p_1): Use known_subrange_p.
gcc/testsuite/
PR middle-end/85164
* gcc.dg/pr85164-1.c, gcc.dg/pr85164-2.c: New tests.
Index: gcc/combine.c
===================================================================
--- gcc/combine.c 2019-03-08 18:15:36.704740334 +0000
+++ gcc/combine.c 2019-04-18 10:11:01.984734102 +0100
@@ -8922,7 +8922,7 @@ force_int_to_mode (rtx x, scalar_int_mod
/* If X is (minus C Y) where C's least set bit is larger than any bit
in the mask, then we may replace with (neg Y). */
if (poly_int_rtx_p (XEXP (x, 0), &const_op0)
- && (unsigned HOST_WIDE_INT) known_alignment (const_op0) > mask)
+ && known_alignment (poly_uint64 (const_op0)) > mask)
{
x = simplify_gen_unary (NEG, xmode, XEXP (x, 1), xmode);
return force_to_mode (x, mode, mask, next_select);
Index: gcc/rtlanal.c
===================================================================
--- gcc/rtlanal.c 2019-03-08 18:14:26.721006369 +0000
+++ gcc/rtlanal.c 2019-04-18 10:11:01.984734102 +0100
@@ -521,7 +521,7 @@ rtx_addr_can_trap_p_1 (const_rtx x, poly
return (!known_size_p (decl_size) || known_eq (decl_size, 0)
? maybe_ne (offset, 0)
- : maybe_gt (offset + size, decl_size));
+ : !known_subrange_p (offset, size, 0, decl_size));
}
return 0;
Index: gcc/testsuite/gcc.dg/pr85164-1.c
===================================================================
--- /dev/null 2019-03-08 11:40:14.606883727 +0000
+++ gcc/testsuite/gcc.dg/pr85164-1.c 2019-04-18 10:11:01.984734102 +0100
@@ -0,0 +1,7 @@
+/* { dg-options "-O2 -w" } */
+a[];
+b;
+c() {
+ unsigned long d;
+ b = a[d - 1 >> 3];
+}
Index: gcc/testsuite/gcc.dg/pr85164-2.c
===================================================================
--- /dev/null 2019-03-08 11:40:14.606883727 +0000
+++ gcc/testsuite/gcc.dg/pr85164-2.c 2019-04-18 10:11:01.984734102 +0100
@@ -0,0 +1,4 @@
+/* { dg-options "-O2 -w" } */
+int a;
+long b;
+void c() { b = -9223372036854775807L - 1 - a; }
