4.4.3 xc32-gcc (32-bit C Compiler)

Although the MPLAB XC32 C/C++ Compiler works with MPLAB X IDE, it must be acquired separately. The full version may be purchased, or a student (limited-feature) version may be downloaded for free. See the Microchip website (www.microchip.com) for details.

A subset of command-line options may be specified in MPLAB X IDE. Select a category and then set up compiler options. For additional options, see the MPLAB X IDE User’s Guide (DS50002027), also available on the Microchip website.

See also 4.4.8 Options Page Features.

Table 4-4. xc32-gcc General Category
Option	Description	Command Line
Enable unaligned access	Enables (or disables) reading and writing of 16- and 32-bit values from addresses that are not 16- or 32-bit aligned. By default, unaligned access is disabled for all pre-ARMv6 and all ARMv6-M architectures and enabled for all other architectures. If unaligned access is not enabled then words in packed data structures are accessed one byte at a time.	`-m[no-]unaligned-access`
Have symbols in production build	Adds debugging information to the generated ELF file.	`-g`
Isolate each function in a section	This option is often used with the linker's `--gc-sections` option to remove unreferenced functions (see the MPLAB® XC32 Assembler, Linker and Utilities User's Guide). Check to place each function into its own section in the output file. The name of the function determines the section’s name in the output file. Note: When you specify this option, the assembler and linker may create larger object and executable files and will be slower executing. Uncheck to place multiple functions in a section.	`-ffunction-sections`
Place data into its own section	This option is often used with the linker's `--gc-section`s option to remove unreferenced statically-allocated variables (see the MPLAB® XC32 Assembler, Linker and Utilities User's Guide). Place each data item into its own section in the output file. The name of the data item determines the name of the section. When you specify this option, the assembler and linker may create larger object and executable files and will also be slower.	`-fdata-sections`
Enable toplevel reordering	Allow reordering of top-level functions, variables, and `asm` statements, such that they might not be output in the same order in which they appear in source files. When this feature is disabled, using the `-fno-toplevel-reorder` option, unreferenced static variables will not be removed. Use this options with optimization level 1 or greater.	`-f[no-]toplevel-reorder`
Use indirect calls	Enable full-range calls, which are typically required when calling a function in another memory region.	`-mlong-calls`

Note that some of the compiler options specified by fields in Project Property Categories other than Optimization can affect the size and execution speed of your project. Consider using the Compiler Advisor, accessible via the MPLAB X IDE Tools > Analysis > Compiler Advisor menu item, to compare the size of your project when built with different combination of compiler options.

Table 4-5. xc32-gcc Optimization Category
Option	Description	Command Line
Optimization Level	Select an optimization level. Your compiler edition may support only some optimizations. Equivalent to `-On` option, where `n` is an option below: `0` - Do not optimize. The compiler’s goal is to reduce the cost of compilation and to make debugging produce the expected results. `1` - Optimize. Optimizing compilation takes somewhat longer, and a lot more host memory for a large function. The compiler tries to reduce code size and execution time. `2` - Optimize even more. The compiler performs nearly all supported optimizations that do not involve a space-speed trade-off. `3` - Optimize yet more favoring speed (superset of O2). `s` - Optimize for size. This level enables all `-O2` optimizations that do not typically increase code size. It also performs further optimizations designed to reduce code size.	`-O0 -O1 -O2 -O3 -Os`
Unroll loops	This option often increases execution speed at the expense of larger code size. Check to 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. Uncheck to not unroll loops.	`-funroll-loops`
Omit frame pointer	Check to not keep the Frame Pointer in a register for functions that don’t need one. Uncheck to keep the Frame Pointer.	`-fomit-frame-pointer`
Pre-optimization instruction scheduling	Attempts to reorder instructions to eliminate instruction stalls. Select "Default for optimization level" for this feature to be controlled purely by the `-O` level selection.	`-f[no-]schedule-insns`
Post-optimization instruction scheduling	Attempts to reorder instructions to eliminate instruction stalls. Select "Default for optimization level" for this feature to be controlled purely by the `-O` level selection.	`-f[no-]schedule-insns2`
Use Common Tentative Definition	Controls the placement of global variables defined without an initializer, known as tentative definitions in the C standard. Tentative definitions are distinct from declarations of a variable with the `extern` keyword, which do not allocate storage. When the feature is enabled, using the `-fcommon` option, storage for uninitialized global objects will be allocated in a common block. This allows the linker to resolve tentative and non-tentative definitions of the same object across translation units. Disabling the feature, using the `-fno-common` option, will have the compiler place uninitialized global objects in the data section of the corresponding object file. Doing so will prevent the linker from associating tentative definitions across translation units, resulting in multiple-definition errors if such definitions are encountered.	`-f[no-]common`.

Table 4-6. xc32-gcc Preprocessing and Messages Category
Option	Description	Command Line
Preprocessor macros	Project-specific preprocessor macro defines passed via the compiler's `–D` option.	`-Dmacro[=defn]`
Include directories	Search these directories for project-specific include files.	`-Ipath`
Make warnings into errors	Check to halt compilation based on warnings as well as errors. Uncheck to halt compilation based on errors only.	`-Werror`
Additional warnings	Check to enable all warnings. Uncheck to disable warnings.	`-Wall`
Enable address warning attribute	Emit a warning for all uses of the `address` attribute. This option is for engineering-support use only.	`-Waddress-attribute-use`
support-ansi	Check to issue all warnings demanded by strict ANSI C. Uncheck to issue all warnings.	`-ansi`
strict-ansi	Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that use forbidden extensions and some other programs that do not follow ISO C and ISO C++.	`-pedantic`