This comes from PR 34389 and it only fails in C++. There is already a testcase:
trunk/gcc/testsuite/g++.dg/warn/Wconversion-pr34389.C
short mask1(short x)
{
short y = 0x7fff;
return x & y; /* { dg-bogus "conversion" "conversion" { xfail *-*-* } 8 } */
}
In C, build_binary_op constructs:
<bit_and_expr 0x2aaaab068200
type <integer_type 0x2aaaab08e540 short int HI
size <integer_cst 0x2aaaab08c930 constant 16>
unit size <integer_cst 0x2aaaab08c960 constant 2>
arg 0 <parm_decl 0x2aaaab095240 x type <integer_type 0x2aaaab08e540 short
int>
arg 1 <var_decl 0x2aaaab161280 y type <integer_type 0x2aaaab08e540 short
int>
while C++ builds:
<bit_and_expr 0x2aaaab21df80
type <integer_type 0x2aaaab08e6c0 int public SI
size <integer_cst 0x2aaaab08ca20 constant 32>
unit size <integer_cst 0x2aaaab08c690 constant 4>
arg 0 <nop_expr 0x2aaaab21df00 type <integer_type 0x2aaaab08e6c0 int>
arg 0 <parm_decl 0x2aaaab095a20 x type <integer_type 0x2aaaab08e540
short int>
arg 1 <nop_expr 0x2aaaab21df40 type <integer_type 0x2aaaab08e6c0 int>
arg 0 <var_decl 0x2aaaab238000 y type <integer_type 0x2aaaab08e540 short
int>
The difference is in shorten_binary_op->common_type. In C, it returns short
int, while in C++ it returns int. If it returned short int in C++, I think it
will avoid warning.
A more robust fix would be to make conversion_warning smart enough to handle
the C++ expression. Not sure how to do that, though.
--
Summary: [C++ only] Wconversion warns for short y = 0x7fff; short
z = (short) x & y;
Product: gcc
Version: unknown
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: manu at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37004
