[PATCH] c, ubsan: Instrument even shortened divisions [PR109151]

[Jakub Jelinek <jakub@redhat.com>]

Hi!

On the following testcase, the C FE decides to shorten the division because
it has a guarantee that INT_MIN / -1 division won't be encountered, the
first operand is widened from narrower unsigned and/or the second operand is
a constant other than all ones (in this case both are true).
The problem is that the narrower type in this case is _Bool and
ubsan_instrument_division only instruments it if op0's type is INTEGER_TYPE
or REAL_TYPE.  Strangely this doesn't happen in C++ FE.
Anyway, we only shorten divisions if the INT_MIN / -1 case is impossible,
so I think we should be fine even with -fstrict-enums in C++ in case it
shortened to ENUMERAL_TYPEs.

The following patch just instruments those on the ubsan_instrument_division
side.  Perhaps only the first hunk and testcase might be needed because
we shouldn't shorten if the other case could be triggered.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk,
or shall I omit the second hunk?

2023-03-17  Jakub Jelinek  <jakub@redhat.com>

	PR c/109151
	* c-ubsan.cc (ubsan_instrument_division): Handle all scalar integral
	types rather than just INTEGER_TYPE.

	* c-c++-common/ubsan/div-by-zero-8.c: New test.

--- gcc/c-family/c-ubsan.cc.jj	2023-02-28 11:38:28.965868044 +0100
+++ gcc/c-family/c-ubsan.cc	2023-03-16 09:49:51.651126302 +0100
@@ -53,7 +53,7 @@ ubsan_instrument_division (location_t lo
   op0 = unshare_expr (op0);
   op1 = unshare_expr (op1);
 
-  if (TREE_CODE (type) == INTEGER_TYPE
+  if (INTEGRAL_TYPE_P (type)
       && sanitize_flags_p (SANITIZE_DIVIDE))
     t = fold_build2 (EQ_EXPR, boolean_type_node,
 		     op1, build_int_cst (type, 0));
@@ -68,7 +68,7 @@ ubsan_instrument_division (location_t lo
     t = NULL_TREE;
 
   /* We check INT_MIN / -1 only for signed types.  */
-  if (TREE_CODE (type) == INTEGER_TYPE
+  if (INTEGRAL_TYPE_P (type)
       && sanitize_flags_p (SANITIZE_SI_OVERFLOW)
       && !TYPE_UNSIGNED (type))
     {
--- gcc/testsuite/c-c++-common/ubsan/div-by-zero-8.c.jj	2023-03-16 10:01:31.626824994 +0100
+++ gcc/testsuite/c-c++-common/ubsan/div-by-zero-8.c	2023-03-16 10:03:05.510443440 +0100
@@ -0,0 +1,14 @@
+/* PR c/109151 */
+/* { dg-do run } */
+/* { dg-options "-fsanitize=integer-divide-by-zero -Wno-div-by-zero -fno-sanitize-recover=integer-divide-by-zero" } */
+/* { dg-shouldfail "ubsan" } */
+
+int d;
+
+int
+main ()
+{
+  d = ((short) (d == 1 | d > 9)) / 0;
+}
+
+/* { dg-output "division by zero" } */

	Jakub