http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51260
Bug #: 51260
Summary: PARAMETER array with constructor initializer:
Compile-time simplify single element access
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: fortran
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: bur...@gcc.gnu.org
Missed optimization in several ways for:
integer, parameter:: is(10000)=(/(i,i=1,10000)/)
print *,is(1)
end
The main issue is that "is(1)" is not simplified into the constant "1".
Expected:
* The front end should already optimize is(1) to "1" and should not generate
the variable to store the parameter.
* One should somehow tell the middle end that only a single element is needed
for I/O. One currently has:
_gfortran_transfer_integer_write (&dt_parm.0, &is[0], 4);
which requires the whole object though only the first 4 bytes are needed (=
&"1").
* The constructor should not be fully expanded, if one only needs a single
element, i.e. using
integer, parameter:: is(*)=(/(i,i=1,10000000)/)
should be quick if one only needs the first element. In any case, no parameter
array should be written if one can simplify it at front-end compilation time.
