inline question

[Mike Kumbera]

I'm having troubles understanding how to get gfortran to inline a
subroutine. This is a simplified example but if I can't inline a 
function that
does a=a+b then I don't have hope for any other functions. What am
I doing wrong? (This example rewritten for gcc DOES inline the function 
call.)

There are two loops in the example program. The top loop calls a subroutine
'simple_add' to do the work and the bottom loop I inlined by hand to do the
exact same work.

                                    time in seconds (lower is better)
                                                top_loop        bottom_loop
gfortran -O0                            18.3                10.7
ifort -O0                                  17.3                10.4

gfortran -O4                            11.5                3.3
ifort -O4                                    3.8                3.3

ifort -O4 -fno-inline-functions 11.43           3.3


I'm using gfortran version:

/usr/apps/gnu/4.3.2/bin/gfortran -v
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-4.3.2/configure 
--prefix=/usr/local/apps/gnu/4.3.2 
--with-mpfr-include=/usr/local/apps/gnu/4.3.2/include 
--with-mpfr-lib=/usr/local/apps/gnu/4.3.2/lib --disable-multilib 
--with-gmp=/usr/local/apps/gnu/4.3.2/lib 
--with-gmp-include=/usr/local/apps/gnu/4.3.2/include 
--enable-languages=c,c++,fortran,java,objc
Thread model: posix
gcc version 4.3.2 (GCC)

----

!The example program
subroutine simple_add (dda, ddb)
implicit none
real*8  dda,ddb

dda = dda + ddb
return
end subroutine

program sum_test
implicit none
real*8 ar,br, cr, cr1
integer k

call system ('date +%s.%N')
ar=1.d0
br=1.d0
cr1=1.d0
do k = 1, 2000000000
call simple_add(cr1,br)
enddo

call system ('date  +%s.%N')
ar=1.d0
br=1.d0
cr=1.d0
do k = 1, 2000000000
cr=cr+br
enddo
call system ('date +%s.%N')

write(*,*) cr1, cr
end