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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/95757] [11 regression] missing warning in
 gcc.dg/Wstringop-overflow-25.c since r11-1517
Date: Fri, 26 Feb 2021 12:12:09 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95757

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |85316
                 CC|                            |amacleod at redhat dot com
           Priority|P3                          |P1

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the warning machinery (or likely the range machinery) is confused about

  size_t r_1_2 =3D UR (1, 2);
  size_t r_2_3 =3D UR (2, 3);

  T (char, S (2), r_1_2);       // { dg-warning "\\\[-Wstringop-overflow"
"pr92814" }

  T (char, S (0), r_2_3);

but it treats the case well when the second T is elided or when the size
computation is moved before the Ts like with

diff --git a/gcc/testsuite/gcc.dg/Wstringop-overflow-25.c
b/gcc/testsuite/gcc.dg/Wstringop-overflow-25.c
index bc609587575..116fbf600a6 100644
--- a/gcc/testsuite/gcc.dg/Wstringop-overflow-25.c
+++ b/gcc/testsuite/gcc.dg/Wstringop-overflow-25.c
@@ -367,16 +367,16 @@ struct Flex
 NOIPA void test_strcpy_malloc_flexarray (void)
 {
   size_t r_0_1 =3D UR (0, 1);
-  size_t r_1_2 =3D UR (1, 2);
-  size_t r_2_3 =3D UR (2, 3);

   T (char, S (0), r_0_1);
   T (char, S (1), r_0_1);       // { dg-warning "\\\[-Wstringop-overflow"
"pr92814" }

+  size_t r_1_2 =3D UR (1, 2);
   T (char, S (0), r_1_2);
   T (char, S (1), r_1_2);
   T (char, S (2), r_1_2);       // { dg-warning "\\\[-Wstringop-overflow"
"pr92814" }

+  size_t r_2_3 =3D UR (2, 3);
   T (char, S (0), r_2_3);
   T (char, S (2), r_2_3);
   T (char, S (3), r_2_3);       // { dg-warning "\\\[-Wstringop-overflow"
"pr92814" }


Martin, is there any harm in changing the testcase this way?  The issue
reproduces with a cross and the two-line snippet at the top (just prune
the rest from the testcase).  In case you want to have a closer look
why the warning is not issued on ppc64le (where I tested) vs. x86_64.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D85316
[Bug 85316] [meta-bug] VRP range propagation missed cases=