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[Bug c++/38027] New: bitfields and -O2 or greater
- From: "john dot spelis at 3dlabs dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 5 Nov 2008 19:21:28 -0000
- Subject: [Bug c++/38027] New: bitfields and -O2 or greater
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
The following program when compiled with gcc 4.1.2 works but with 4.3.0 it
produces incorrect output at optimisation level O2 or greater.
/ * ------ */
#include <iostream>
#include <stdio.h>
using namespace std;
typedef unsigned int uint32_t;
typedef unsigned short uint16_t;
typedef unsigned char uint8_t;
class CColourARGB4444;
class CColourARGB8888
{
public :
union
{
struct
{
uint32_t mBlue : 8;
uint32_t mGreen : 8;
uint32_t mRed : 8;
uint32_t mAlpha : 8;
} mBits;
uint32_t mWord;
} mCol;
CColourARGB8888(const CColourARGB4444 &rhs);
};
class CColourARGB4444
{
public :
union
{
struct
{
uint16_t mBlue : 4;
uint16_t mGreen : 4;
uint16_t mRed : 4;
uint16_t mAlpha : 4;
} mBits;
uint16_t mWord;
} mCol;
public :
/// CColourARGB4444 constructor
CColourARGB4444(const uint8_t &alpha, const uint8_t &red, const uint8_t
&green, const uint8_t &blue)
{ mCol.mBits.mAlpha = alpha; mCol.mBits.mRed = red; mCol.mBits.mGreen =
green; mCol.mBits.mBlue = blue; }
};
__inline CColourARGB8888::CColourARGB8888(const CColourARGB4444 &rhs)
{
mCol.mBits.mRed = ((rhs.mCol.mBits.mRed << 4) & 0xF0) |
rhs.mCol.mBits.mRed;
mCol.mBits.mGreen = ((rhs.mCol.mBits.mGreen << 4) & 0xF0) |
rhs.mCol.mBits.mGreen;
mCol.mBits.mBlue = ((rhs.mCol.mBits.mBlue << 4) & 0xF0) |
rhs.mCol.mBits.mBlue;
mCol.mBits.mAlpha = ((rhs.mCol.mBits.mAlpha << 4) & 0xF0) |
rhs.mCol.mBits.mAlpha;
printf("Constructing CColourARGB8888 %x from CColourARGB4444 %x\n",
mCol.mWord, rhs.mCol.mWord);
}
void broken()
{
for (uint8_t y = 0; y < 4; ++y) {
for (uint8_t x = 0; x < 4; ++x) {
CColourARGB4444 c4(0xF, x, y, 0);
CColourARGB8888 c8(c4);
}
}
}
CColourARGB4444 myfoo(uint8_t XT, uint8_t YT) {
return CColourARGB4444(0xF, XT, YT, 0);
}
void ok()
{
for (uint8_t y = 0; y < 4; ++y) {
for (uint8_t x = 0; x < 4; ++x) {
CColourARGB4444 c4 = myfoo(x, y);
CColourARGB8888 c8(c4);
}
}
}
int main()
{
printf("this\n");
ok();
printf("that\n");
broken();
}
/* --- end --- */
When not working the bit fields have not been updated, e.g. a broken case
output is;
Constructing CColourARGB8888 ff000000 from CColourARGB4444 f330
When working the output has updated bitfields, e.g.
Constructing CColourARGB8888 ff333300 from CColourARGB4444 f330
--
Summary: bitfields and -O2 or greater
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: john dot spelis at 3dlabs dot com
GCC build triplet: i686-pc-linux
GCC host triplet: i686-pc-linux
GCC target triplet: i686-pc-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38027