[Bug target/49446] New: avr-g++ does not optimize when using bitshift in inlined function

[gcc at emailgo dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49446

           Summary: avr-g++ does not optimize when using bitshift in
                    inlined function
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: gcc@emailgo.de


Hi,

so you wanted an *.i* file, I don't think this will be helpful. Anyway I
appended it.

I have a structure like this:

function call <- inline function <- inline function.

If the first Inline function (Button::Poll that is) passes a const number as
parameter pin_number to the second function (Port::get_pin) that is, then the
Poll::get_pin function returns *port_address & (1<<pin_number). That masks the
appropiate pin in the port (bit in byte). However that will be static, but only
optimize to some right rotates and then a compare against zero. It would be
possible to just use the AVR's sbis (if bit is set) and provide the pin_number.
And in fact that is the case when I call get_pin with (1<<pin_number) as
parameter and don't do the shifting in the second-level inline function (but in
the first).

I hope you understand what I mean. This issue might also apply to other
Platforms where this could be optimized.

My command was :  ./avr-gcc-4.6.0 -S -mmcu=atmega8 -Os
/home/oliver/AVR/io/test.cc -save-temps -v

and it's output:

Using built-in specs.
COLLECT_GCC=./avr-gcc-4.6.0
COLLECT_LTO_WRAPPER=/usr/local/avr/libexec/gcc/avr/4.6.0/lto-wrapper
Target: avr
Configured with: ../configure --target=avr --prefix=/usr/local/avr
--disable-nls --enable-languages=c,c++ --disable-libssp : (reconfigured)
../configure --target=avr --prefix=/usr/local/avr --disable-nls
--enable-languages=c,c++ --disable-libssp
Thread model: single
gcc version 4.6.0 (GCC) 
COLLECT_GCC_OPTIONS='-S' '-mmcu=atmega8' '-Os' '-save-temps' '-v'
 /usr/local/avr/libexec/gcc/avr/4.6.0/cc1plus -E -quiet -v -imultilib avr4
/home/oliver/AVR/io/test.cc -mmcu=atmega8 -Os -fpch-preprocess -fno-rtti
-fno-enforce-eh-specs -fno-exceptions -o test.ii
ignoring nonexistent directory
"/usr/local/avr/lib/gcc/avr/4.6.0/../../../../avr/include/c++/4.6.0"
ignoring nonexistent directory
"/usr/local/avr/lib/gcc/avr/4.6.0/../../../../avr/include/c++/4.6.0/avr/avr4"
ignoring nonexistent directory
"/usr/local/avr/lib/gcc/avr/4.6.0/../../../../avr/include/c++/4.6.0/backward"
ignoring nonexistent directory
"/usr/local/avr/lib/gcc/avr/4.6.0/../../../../avr/sys-include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/avr/lib/gcc/avr/4.6.0/include
 /usr/local/avr/lib/gcc/avr/4.6.0/include-fixed
 /usr/local/avr/lib/gcc/avr/4.6.0/../../../../avr/include
End of search list.
COLLECT_GCC_OPTIONS='-S' '-mmcu=atmega8' '-Os' '-save-temps' '-v'
 /usr/local/avr/libexec/gcc/avr/4.6.0/cc1plus -fpreprocessed test.ii -quiet
-dumpbase test.cc -mmcu=atmega8 -auxbase test -Os -version -o test.s -fno-rtti
-fno-enforce-eh-specs -fno-exceptions
GNU C++ (GCC) version 4.6.0 (avr)
    compiled by GNU C version 4.6.1 20110526 (prerelease), GMP version 5.0.1,
MPFR version 3.0.1-p3, MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++ (GCC) version 4.6.0 (avr)
    compiled by GNU C version 4.6.1 20110526 (prerelease), GMP version 5.0.1,
MPFR version 3.0.1-p3, MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: bed1f0f30349434b4d9bd9c4315cba61
COMPILER_PATH=/usr/local/avr/libexec/gcc/avr/4.6.0/:/usr/local/avr/libexec/gcc/avr/4.6.0/:/usr/local/avr/libexec/gcc/avr/:/usr/local/avr/lib/gcc/avr/4.6.0/:/usr/local/avr/lib/gcc/avr/
LIBRARY_PATH=/usr/local/avr/lib/gcc/avr/4.6.0/avr4/:/usr/local/avr/lib/gcc/avr/4.6.0/../../../../avr/lib/avr4/:/usr/local/avr/lib/gcc/avr/4.6.0/:/usr/local/avr/lib/gcc/avr/4.6.0/../../../../avr/lib/
COLLECT_GCC_OPTIONS='-S' '-mmcu=atmega8' '-Os' '-save-temps' '-v'


Have fun!