https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70774
Bug ID: 70774
Summary: constexpr function with reference parameter gives
reinterpret_cast from integer to pointer error
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: steven.spark at gmail dot com
Target Milestone: ---
Here is the simplified code:
--------------
#define PORTX (*(volatile unsigned char *)(0x1B))
constexpr volatile unsigned char * testRef(volatile unsigned char & x) {
return &x;
}
volatile unsigned char* addr = testRef(PORTX); /// OK
constexpr volatile unsigned char* addr2 = testRef(PORTX); /// error:
/// reinterpret_cast from integer to pointer
--------------
This compiled without problem with gcc 4.8.1, but fails with 4.9.2.
Using built-in specs.
COLLECT_GCC=avr-g++.exe
Target: avr
Configured with:
/home/toolsbuild/workspace/avr8-gnu-toolchain/src/gcc/configure
LDFLAGS=-L/home/toolsbuild/workspace/avr8-gnu-toolchain/avr8-gnu-toolchain-win32_x86-hostlibs/lib
CPPFLAGS= --target=avr --host=i686-w64-mingw32 --build=x86_64-pc-linux-gnu
--prefix=/home/toolsbuild/workspace/avr8-gnu-toolchain/avr8-gnu-toolchain-win32_x86
--libdir=/home/toolsbuild/workspace/avr8-gnu-toolchain/avr8-gnu-toolchain-win32_x86/lib
--enable-languages=c,c++ --with-dwarf2 --enable-doc --disable-shared
--disable-libada --disable-libssp --disable-nls --with-avrlibc=yes
--with-mpfr=/home/toolsbuild/workspace/avr8-gnu-toolchain/avr8-gnu-toolchain-win32_x86-hostlibs
--with-gmp=/home/toolsbuild/workspace/avr8-gnu-toolchain/avr8-gnu-toolchain-win32_x86-hostlibs
--with-mpc=/home/toolsbuild/workspace/avr8-gnu-toolchain/avr8-gnu-toolchain-win32_x86-hostlibs
--enable-win32-registry=avrtoolchain
--with-pkgversion=AVR_8_bit_GNU_Toolchain_3.5.0_1662
--with-bugurl=http://www.atmel.com
Thread model: single
gcc version 4.9.2 (AVR_8_bit_GNU_Toolchain_3.5.0_1662)
I'm writing code for AVR micro controller where every byte counts, so compile
time evaluation is key. I was trying out the new Atmel Studio 7 IDE which comes
with the new 4.9.2 gcc when I came across this problem. In my real world code
I'm using constexpr constructor and constexpr instances of my pin handler class
- to make life easier and encapsulate port, data direction and other registers.
Note: If I use pointer instead of reference then it compiles fine:
constexpr volatile unsigned char * testAddr(volatile unsigned char * x) {
return x;
}
constexpr volatile unsigned char* addr3 = testAddr(&PORTX); /// OK
Why is this? Am I doing something wrong? How can I use (port) references in
constexpr functions?
This also does NOT work:
constexpr volatile unsigned char& ref5 = PORTX; /// error
