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
-fthread-jumps Perform optimizations where a check is made to see if a jump
branches to a location where another comparison subsumed
by the first is found. If so, the first branch is redirected to either
the destination of the second branch or a point immediately
following it, depending on whether the condition is known to
be true or false.
-funroll-loops Perform the optimization of loop unrolling. This is only done
for loops whose number of iterations can be determined at
compile time or run time. -funroll-loops implies both
-fstrength-reduce and -frerun-cse-after-loop.
-funroll-all-loops Perform the optimization of loop unrolling. This is done for all
loops and usually makes programs run more slowly.
-funroll-all-loops implies -fstrength-reduce, as
well as -frerun-cse-after-loop.
Options of the form -fflag specify machine-independent flags. Most flags have both
positive and negative forms; the negative form of -ffoo would be -fno-foo. In the
table below, only one of the forms is listed (the one that is not the default.)
TABLE 3-10: MACHINE-INDEPENDENT OPTIMIZATION OPTIONS
Option Definition
-fforce-mem Force memory operands to be copied into registers
before doing arithmetic on them. This produces better
code by making all memory references potential common
subexpressions. When they are not common subexpressions,
instruction combination should eliminate the
separate register-load. The -O2 option turns on this
option.
-finline-functions Integrate all simple functions into their callers. The
compiler heuristically decides which functions are simple
enough to be worth integrating in this way. If all calls to a
given function are integrated, and the function is declared
static, then the function is normally not output as
assembler code in its own right.
-finline-limit=n By default, the compiler limits the size of functions that
can be inlined. This flag allows the control of this limit for
functions that are explicitly marked as inline (i.e., marked
with the inline keyword). n is the size of functions that
can be inlined in number of pseudo instructions (not
counting parameter handling). The default value of n is
10000. Increasing this value can result in more inlined
code at the cost of compilation time and memory
consumption.
Decreasing usually makes the compilation faster and less
code will be inlined (which presumably means slower
programs). This option is particularly useful for programs
that use inlining.
Note: Pseudo instruction represents, in this particular
context, an abstract measurement of function’s size. In no
way does it represent a count of assembly instructions
and as such, its exact meaning might change from one
release of the compiler to an another.
DS51284H-page 50 © 2008 Microchip Technology Inc.