I add -Os -Wall flags to every avr-g++ command. During coding I've noticed g++
adds plenty of unnecessary assembly to output file. I'll try to check it with
gcc 4.x but currently I fail to compile it.
Problem is related to static initialization of template class/struct variable.
Following code snippet should explain the issue. I've tried to make it minimal.
I'd be happy even with some work-around like __attribute__ but not with 'use
macros instead' which I hear constantly...
Hope this helps someone.
/*
Reading specs from /usr/lib/gcc/avr/3.4.6/specs
Configured with:
/var/tmp/cross/avr/portage/cross-avr/gcc-3.4.6/work/gcc-3.4.6/configure
--prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/avr/gcc-bin/3.4.6
--includedir=/usr/lib/gcc/avr/3.4.6/include
--datadir=/usr/share/gcc-data/avr/3.4.6
--mandir=/usr/share/gcc-data/avr/3.4.6/man
--infodir=/usr/share/gcc-data/avr/3.4.6/info
--with-gxx-include-dir=/usr/lib/gcc/avr/3.4.6/include/g++-v3
--host=x86_64-pc-linux-gnu --target=avr --build=x86_64-pc-linux-gnu
--disable-altivec --enable-nls --without-included-gettext --with-system-zlib
--disable-checking --disable-werror --enable-secureplt
--disable-libunwind-exceptions --disable-libgcj --enable-languages=c,c++
--enable-shared --disable-threads
Thread model: single
gcc version 3.4.6 (Gentoo 3.4.6, ssp-3.4.5-1.0, pie-8.7.9)
(Can't successfully build 4.x yet)
i686 4.1.2 version also generates additional code in one case
but the code is much smaller.
*/
/* Declaration of Real */
struct stub {
float D;
stub() {}
stub(float A) : D(A) {}
inline operator float&() { return D; }
inline operator const float&() const { return D; }
};
//typedef float Real; /* No problems if real is simply a float */
typedef stub Real;
/*** Template using previously defined type ***/
#define OUTER 0 /* No problem if we use static variable not from the template
*/
#if OUTER == 1
static Real Result;
#endif
template<int Dummy> /* When there's no template code is ok */
struct Avg {
#if OUTER == 0
static Real Result;
#endif
static const Real &Push(const Real Value) {
Result *= Dummy;
// Result *= 20 /* No problems if we won't touch dummy */
return Result;
}
};
#if OUTER == 0
template<int Dummy>
Real Avg<Dummy>::Result;
#endif
int main()
{
Avg<20>::Push(1.0);
return 0;
}
#if 0
Unnecessary code generated looks like this:
.type _GLOBAL__I_main, @function
_GLOBAL__I_main:
/* prologue: frame size=0 */
push r2
push r3
push r4
push r5
push r6
push r7
push r8
push r9
push r10
push r11
push r12
push r13
push r14
push r15
push r16
push r17
/* prologue end (size=16) */
lds r18,_ZGVN3AvgILi20EE6ResultE
lds r19,_ZGVN3AvgILi20EE6ResultE+1
lds r20,_ZGVN3AvgILi20EE6ResultE+2
lds r21,_ZGVN3AvgILi20EE6ResultE+3
lds r22,_ZGVN3AvgILi20EE6ResultE+4
lds r23,_ZGVN3AvgILi20EE6ResultE+5
lds r24,_ZGVN3AvgILi20EE6ResultE+6
lds r25,_ZGVN3AvgILi20EE6ResultE+7
ldi r30,lo8(1)
mov r2,r30
clr r3
mov r4,r3
mov r5,r3
mov r6,r3
mov r7,r3
mov r8,r3
mov r9,r3
mov r10,r18
add r10,r2
mov r30,r2
cp r10,r18
brlo .L7
mov r30,r3
.L7:
mov r11,r19
add r11,r3
ldi r26,lo8(1)
cp r11,r19
brlo .L8
ldi r26,lo8(0)
.L8:
add r30,r11
ldi r31,lo8(1)
cp r30,r11
brlo .L9
ldi r31,lo8(0)
.L9:
or r26,r31
mov r11,r30
mov r12,r20
add r12,r4
ldi r27,lo8(1)
cp r12,r20
brlo .L10
ldi r27,lo8(0)
.L10:
mov r30,r26
add r30,r12
ldi r31,lo8(1)
cp r30,r12
brlo .L11
ldi r31,lo8(0)
.L11:
or r27,r31
mov r12,r30
mov r13,r21
add r13,r5
ldi r26,lo8(1)
cp r13,r21
brlo .L12
ldi r26,lo8(0)
.L12:
mov r30,r27
add r30,r13
ldi r31,lo8(1)
cp r30,r13
brlo .L13
ldi r31,lo8(0)
.L13:
or r26,r31
mov r13,r30
mov r14,r22
add r14,r6
ldi r27,lo8(1)
cp r14,r22
brlo .L14
ldi r27,lo8(0)
.L14:
mov r30,r26
add r30,r14
ldi r31,lo8(1)
cp r30,r14
brlo .L15
ldi r31,lo8(0)
.L15:
or r27,r31
mov r14,r30
mov r15,r23
add r15,r7
ldi r26,lo8(1)
cp r15,r23
brlo .L16
ldi r26,lo8(0)
.L16:
mov r30,r27
add r30,r15
ldi r31,lo8(1)
cp r30,r15
brlo .L17
ldi r31,lo8(0)
.L17:
or r26,r31
mov r15,r30
mov r16,r24
add r16,r8
ldi r27,lo8(1)
cp r16,r24
brlo .L18
ldi r27,lo8(0)
.L18:
mov r31,r26
add r31,r16
ldi r30,lo8(1)
cp r31,r16
brlo .L19
ldi r30,lo8(0)
.L19:
or r30,r27
mov r17,r25
add r17,r9
add r30,r17
sts _ZGVN3AvgILi20EE6ResultE,r10
sts _ZGVN3AvgILi20EE6ResultE+1,r11
sts _ZGVN3AvgILi20EE6ResultE+2,r12
sts _ZGVN3AvgILi20EE6ResultE+3,r13
sts _ZGVN3AvgILi20EE6ResultE+4,r14
sts _ZGVN3AvgILi20EE6ResultE+5,r15
sts _ZGVN3AvgILi20EE6ResultE+6,r31
sts _ZGVN3AvgILi20EE6ResultE+7,r30
/* epilogue: frame size=0 */
pop r17
pop r16
pop r15
pop r14
pop r13
pop r12
pop r11
pop r10
pop r9
pop r8
pop r7
pop r6
pop r5
pop r4
pop r3
pop r2
ret
#endif
--
Summary: Lots of (possibly) unnecesary static initialization code
generated.
Product: gcc
Version: 3.4.6
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: bla at thera dot be
GCC build triplet: x86_64-pc-linux-gnu
GCC host triplet: x86_64-pc-linux-gnu
GCC target triplet: avr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36310
