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

16-Bit C Compiler User’s Guide
TABLE 3-9: SPECIFIC OPTIMIZATION OPTIONS (CONTINUED)
Option Definition
-fcse-follow-jumps In common subexpression elimination, scan through jump
instructions when the target of the jump is not reached by any
other path. For example, when CSE encounters an if
statement with an else clause, CSE will follow the jump when
the condition tested is false.
-fcse-skip-blocks This is similar to -fcse-follow-jumps, but causes CSE to
follow jumps which conditionally skip over blocks. When CSE
encounters a simple if statement with no else clause,
-fcse-skip-blocks causes CSE to follow the jump around
the body of the if.
-fexpensiveoptimizations
-ffunction-sections
-fdata-sections
Perform a number of minor optimizations that are relatively
expensive.
Place each function or data item into its own section in the
output file. The name of the function or the name of the data
item determines the section’s name in the output file.
Only use these options when there are significant benefits for
doing so. When you specify these options, the assembler and
linker may create larger object and executable files and will
also be slower.
-fgcse Perform a global common subexpression elimination pass.
This pass also performs global constant and copy
propagation.
-fgcse-lm When -fgcse-lm is enabled, global common subexpression
elimination will attempt to move loads which are only killed by
stores into themselves. This allows a loop containing a
load/store sequence to be changed to a load outside the loop,
and a copy/store within the loop.
-fgcse-sm When -fgcse-sm is enabled, a store motion pass is run after
global common subexpression elimination. This pass will
attempt to move stores out of loops. When used in conjunction
with -fgcse-lm, loops containing a load/store sequence can
be changed to a load before the loop and a store after the
loop.
-fmove-all-movables Forces all invariant computations in loops to be moved outside
the loop.
-fno-defer-pop Always pop the arguments to each function call as soon as
that function returns. The compiler normally lets arguments
accumulate on the stack for several function calls and pops
them all at once.
-fno-peephole
-fno-peephole2
-foptimizeregister-move
-fregmove
Disable machine specific peephole optimizations. Peephole
optimizations occur at various points during the compilation.
-fno-peephole disables peephole optimization on machine
instructions, while -fno-peephole2 disables high level
peephole optimizations. To disable peephole entirely, use both
options.
Attempt to reassign register numbers in move instructions and
as operands of other simple instructions in order to maximize
the amount of register tying.
-fregmove and -foptimize-register-moves are the
same optimization.
DS51284H-page 48 © 2008 Microchip Technology Inc.