Re: [PATCH] middle-end/108995 - avoid folding when sanitizing overflow

[Richard Biener <rguenther@suse.de>]

On Thu, 9 Mar 2023, Jakub Jelinek wrote:

> On Wed, Mar 08, 2023 at 09:38:43AM +0000, Richard Biener via Gcc-patches wrote:
> > The following plugs one place in extract_muldiv where it should avoid
> > folding when sanitizing overflow.
> > 
> > I'm unsure about the testcase, I didn't find any that tests for
> > a runtime sanitizer error ...
> > 
> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
> > 
> > OK?
> > 
> > 	PR middle-end/108995
> > 	* fold-const.cc (extract_muldiv_1): Avoid folding
> > 	(CST * b) / CST2 when sanitizing overflow and we rely on
> > 	overflow being undefined.
> 
> This is ok.
> 
> > 
> > 	* gcc.dg/ubsan/pr108995.c: New testcase.
> 
> As for testcase, there are many testcases that test for runtime sanitizer
> errors.  For ubsan, it is more common to test -fsanitize-recover= and
> just dg-output scan the output for expected diagnostics (many examples
> in that directory).
> Another possibility is to test for the no recovery, see e.g.
> gcc.dg/ubsan/bounds-3.c.  In that case there should be
> /* { dg-do run } */
> and
> /* { dg-shouldfail "ubsan" } */
> but dg-output checking for the exact wording is still highly desirable.
> 
> The test also relies on 32-bit ints, so it should be dg-do run { target int32 }
> I think.

OK, the following is what I have applied.

Richard.

From ace65db9215882b95e2ead1bb0dc8c54c2ea69be Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Wed, 8 Mar 2023 09:06:44 +0100
Subject: [PATCH] middle-end/108995 - avoid folding when sanitizing overflow
To: gcc-patches@gcc.gnu.org

The following plugs one place in extract_muldiv where it should avoid
folding when sanitizing overflow.

	PR middle-end/108995
	* fold-const.cc (extract_muldiv_1): Avoid folding
	(CST * b) / CST2 when sanitizing overflow and we rely on
	overflow being undefined.

	* gcc.dg/ubsan/pr108995.c: New testcase.
---
 gcc/fold-const.cc                     |  7 +++----
 gcc/testsuite/gcc.dg/ubsan/pr108995.c | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/ubsan/pr108995.c

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 99882ef820a..02a24c5fe65 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -7093,6 +7093,7 @@ extract_muldiv_1 (tree t, tree c, enum tree_code code, tree wide_type,
 	 If we have an unsigned type, we cannot do this since it will change
 	 the result if the original computation overflowed.  */
       if (TYPE_OVERFLOW_UNDEFINED (ctype)
+	  && !TYPE_OVERFLOW_SANITIZED (ctype)
 	  && ((code == MULT_EXPR && tcode == EXACT_DIV_EXPR)
 	      || (tcode == MULT_EXPR
 		  && code != TRUNC_MOD_EXPR && code != CEIL_MOD_EXPR
@@ -7102,8 +7103,7 @@ extract_muldiv_1 (tree t, tree c, enum tree_code code, tree wide_type,
 	  if (wi::multiple_of_p (wi::to_wide (op1), wi::to_wide (c),
 				 TYPE_SIGN (type)))
 	    {
-	      if (TYPE_OVERFLOW_UNDEFINED (ctype))
-		*strict_overflow_p = true;
+	      *strict_overflow_p = true;
 	      return fold_build2 (tcode, ctype, fold_convert (ctype, op0),
 				  fold_convert (ctype,
 						const_binop (TRUNC_DIV_EXPR,
@@ -7112,8 +7112,7 @@ extract_muldiv_1 (tree t, tree c, enum tree_code code, tree wide_type,
 	  else if (wi::multiple_of_p (wi::to_wide (c), wi::to_wide (op1),
 				      TYPE_SIGN (type)))
 	    {
-	      if (TYPE_OVERFLOW_UNDEFINED (ctype))
-		*strict_overflow_p = true;
+	      *strict_overflow_p = true;
 	      return fold_build2 (code, ctype, fold_convert (ctype, op0),
 				  fold_convert (ctype,
 						const_binop (TRUNC_DIV_EXPR,
diff --git a/gcc/testsuite/gcc.dg/ubsan/pr108995.c b/gcc/testsuite/gcc.dg/ubsan/pr108995.c
new file mode 100644
index 00000000000..166825b2ef8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ubsan/pr108995.c
@@ -0,0 +1,18 @@
+/* { dg-do run { target int32 } } */
+/* { dg-shouldfail "ubsan" } */
+/* With optimization we constant fold and diagnose the overflow and do
+   not sanitize anything.  */
+/* { dg-skip-if "" { *-*-* } { "*" } { ! "-O0" } } */
+/* { dg-options "-fsanitize=undefined -fno-sanitize-recover=undefined" } */
+
+int a;
+const int b = 44514;
+int *c = &a;
+
+int main ()
+{
+  *c = 65526 * b / 6;
+  return 0;
+}
+
+/* { dg-output "signed integer overflow: 44514 \\* 65526 cannot be represented in type 'int'" } */
-- 
2.35.3