MPLAB C Compiler for PIC24 MCUs and dsPIC DSCs ... - Microchip

16-Bit C Compiler User’s Guide
3.5.5 Options for Debugging
The following options are used for debugging.
TABLE 3-7: DEBUGGING OPTIONS
Option Definition
-g Produce debugging information.
The compiler supports the use of -g with -O making it possible
to debug optimized code. The shortcuts taken by optimized code
may occasionally produce surprising results:
• Some declared variables may not exist at all;
• Flow of control may briefly move unexpectedly;
• Some statements may not be executed because they
compute constant results or their values were already at
hand;
• Some statements may execute in different places because
they were moved out of loops.
Nevertheless it proves possible to debug optimized output. This
makes it reasonable to use the optimizer for programs that might
have bugs.
-Q Makes the compiler print out each function name as it is
compiled, and print some statistics about each pass when it
finishes.
-save-temps Don’t delete intermediate files. Place them in the current directory
and name them based on the source file. Thus, compiling
foo.c with -c -save-temps would produce the following
files:
foo.i (preprocessed file)
foo.p (pre procedure abstraction assembly language file)
foo.s (assembly language file)
foo.o (object file)
3.5.6 Options for Controlling Optimization
The following options control compiler optimizations.
TABLE 3-8: GENERAL OPTIMIZATION OPTIONS
Option Definition
-O0 Do not optimize. (This is the default.)
Without -O, the compiler’s goal is to reduce the cost of compilation
and to make debugging produce the expected results.
Statements are independent: if you stop the program with a
breakpoint between statements, you can then assign a new
value to any variable or change the program counter to any
other statement in the function and get exactly the results you
would expect from the source code.
The compiler only allocates variables declared register in
registers.
-O
-O1
Optimize. Optimizing compilation takes somewhat longer, and
a lot more host memory for a large function.
With -O, the compiler tries to reduce code size and execution
time.
When -O is specified, the compiler turns on
-fthread-jumps and
-fdefer-pop. The compiler turns on
-fomit-frame-pointer.
DS51284H-page 46 © 2008 Microchip Technology Inc.