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<H2><A NAME="SECTION00563000000000000000">
4.6.3 Environment Variables</A>
</H2>

<P>
There is a number of environmental variables that can be used when
running SDCC to enable certain optimizations or force a specific program
behaviour. these variables are primarily for debugging purposes so
they can be enabled/disabled at will.

<P>
Currently there is only two such variables available:
<DL>
<DT><STRONG>OPTIMIZE_BITFIELD_POINTER_GET<A NAME="3098"></A><A NAME="3099"></A></STRONG></DT>
<DD>When
this variable exists, reading of structure bitfields is optimized
by directly loading FSR0 with the address of the bitfield structure.
Normally SDCC will cast the bitfield structure to a bitfield pointer
and then load FSR0. This step saves data ram and code space for functions
that make heavy use of bitfields. (i.e., 80 bytes of code space are
saved when compiling malloc.c with this option). 
</DD>
<DT><STRONG>NO_REG_OPT<A NAME="3100"></A><A NAME="3101"></A></STRONG></DT>
<DD>Do
not perform pCode registers optimization. This should be used for
debugging purposes. If bugs in the pcode optimizer are found, users
can benefit from temporarily disabling the optimizer until the bug
is fixed.
</DD>
</DL>

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2011-03-20
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