The following fixes PR70143. Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.
Richard. 2016-03-09 Richard Biener <rguent...@suse.de> c-family/ PR c/70143 * c-common.c (strict_aliasing_warning): Add back alias_sets_conflict_p check. * gcc.dg/Wstrict-aliasing-bogus-upcast.c: New testcase. * gcc.dg/Wstrict-aliasing-struct-with-char-member.c: Likewise. * gcc.dg/Wstrict-aliasing-struct-member.c: Remove again. Index: gcc/c-family/c-common.c =================================================================== *** gcc/c-family/c-common.c (revision 234025) --- gcc/c-family/c-common.c (working copy) *************** strict_aliasing_warning (tree otype, tre *** 1568,1574 **** alias_set_type set2 = get_alias_set (TREE_TYPE (type)); if (set1 != set2 && set2 != 0 ! && (set1 == 0 || !alias_set_subset_of (set2, set1))) { warning (OPT_Wstrict_aliasing, "dereferencing type-punned " "pointer will break strict-aliasing rules"); --- 1568,1576 ---- alias_set_type set2 = get_alias_set (TREE_TYPE (type)); if (set1 != set2 && set2 != 0 ! && (set1 == 0 ! || (!alias_set_subset_of (set2, set1) ! && !alias_sets_conflict_p (set1, set2)))) { warning (OPT_Wstrict_aliasing, "dereferencing type-punned " "pointer will break strict-aliasing rules"); Index: gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-upcast.c =================================================================== *** gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-upcast.c (revision 0) --- gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-upcast.c (working copy) *************** *** 0 **** --- 1,17 ---- + /* { dg-do compile } */ + /* { dg-options "-O2 -Wall" } */ + + struct a { + int i; + }; + struct b { + struct a a; + int j; + }; + int main(void) + { + static struct b b; + struct a *ap=(struct a *)&b; + return ((struct b *)&ap->i)->j; /* { dg-bogus "will break strict-aliasing" } */ + } + Index: gcc/testsuite/gcc.dg/Wstrict-aliasing-struct-with-char-member.c =================================================================== --- gcc/testsuite/gcc.dg/Wstrict-aliasing-struct-with-char-member.c (revision 0) +++ gcc/testsuite/gcc.dg/Wstrict-aliasing-struct-with-char-member.c (working copy) @@ -0,0 +1,16 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -Wall" } */ + +struct a { + int i; + char c; +}; +struct b { + float f; + float g; +}; +int main(void) +{ + static struct b b; + return ((struct a *)&b)->i; /* { dg-warning "will break strict-aliasing" } */ +}