Using the GNU Compiler Collection (GCC)

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MIPS Options

These -m options are defined for the MIPS family of computers:

-march=cpu-type: Assume the defaults for the machine type cpu-type when generating instructions. The choices for cpu-type are r2000, r3000, r3900, r4000, r4100, r4300, r4400, r4600, r4650, r5000, r6000, r8000, and orion. Additionally, the r2000, r3000, r4000, r5000, and r6000 can be abbreviated as r2k (or r2K), r3k, etc.
-mtune=cpu-type: Assume the defaults for the machine type cpu-type when scheduling instructions. The choices for cpu-type are r2000, r3000, r3900, r4000, r4100, r4300, r4400, r4600, r4650, r5000, r6000, r8000, and orion. Additionally, the r2000, r3000, r4000, r5000, and r6000 can be abbreviated as r2k (or r2K), r3k, etc. While picking a specific cpu-type will schedule things appropriately for that particular chip, the compiler will not generate any code that does not meet level 1 of the MIPS ISA (instruction set architecture) without a -mipsX or -mabi switch being used.
-mcpu=cpu-type: This is identical to specifying both -march and -mtune.
-mips1: Issue instructions from level 1 of the MIPS ISA. This is the default. r3000 is the default cpu-type at this ISA level.
-mips2: Issue instructions from level 2 of the MIPS ISA (branch likely, square root instructions). r6000 is the default cpu-type at this ISA level.
-mips3: Issue instructions from level 3 of the MIPS ISA (64-bit instructions). r4000 is the default cpu-type at this ISA level.
-mips4: Issue instructions from level 4 of the MIPS ISA (conditional move, prefetch, enhanced FPU instructions). r8000 is the default cpu-type at this ISA level.
-mfp32: Assume that 32 32-bit floating point registers are available. This is the default.
-mfp64: Assume that 32 64-bit floating point registers are available. This is the default when the -mips3 option is used.
-mfused-madd
-mno-fused-madd: Generate code that uses (does not use) the floating point multiply and accumulate instructions, when they are available. These instructions are generated by default if they are available, but this may be undesirable if the extra precision causes problems or on certain chips in the mode where denormals are rounded to zero where denormals generated by multiply and accumulate instructions cause exceptions anyway.
-mgp32: Assume that 32 32-bit general purpose registers are available. This is the default.
-mgp64: Assume that 32 64-bit general purpose registers are available. This is the default when the -mips3 option is used.
-mint64: Force int and long types to be 64 bits wide. See -mlong32 for an explanation of the default, and the width of pointers.
-mlong64: Force long types to be 64 bits wide. See -mlong32 for an explanation of the default, and the width of pointers.
-mlong32: Force long, int, and pointer types to be 32 bits wide.
If none of -mlong32, -mlong64, or -mint64 are set, the size of ints, longs, and pointers depends on the ABI and ISA chosen. For -mabi=32, and -mabi=n32, ints and longs are 32 bits wide. For -mabi=64, ints are 32 bits, and longs are 64 bits wide. For -mabi=eabi and either -mips1 or -mips2, ints and longs are 32 bits wide. For -mabi=eabi and higher ISAs, ints are 32 bits, and longs are 64 bits wide. The width of pointer types is the smaller of the width of longs or the width of general purpose registers (which in turn depends on the ISA).
-mabi=32
-mabi=o64
-mabi=n32
-mabi=64
-mabi=eabi: Generate code for the indicated ABI. The default instruction level is -mips1 for 32, -mips3 for n32, and -mips4 otherwise. Conversely, with -mips1 or -mips2, the default ABI is 32; otherwise, the default ABI is 64.
-mmips-as: Generate code for the MIPS assembler, and invoke mips-tfile to add normal debug information. This is the default for all platforms except for the OSF/1 reference platform, using the OSF/rose object format. If the either of the -gstabs or -gstabs+ switches are used, the mips-tfile program will encapsulate the stabs within MIPS ECOFF.
-mgas: Generate code for the GNU assembler. This is the default on the OSF/1 reference platform, using the OSF/rose object format. Also, this is the default if the configure option --with-gnu-as is used.
-msplit-addresses
-mno-split-addresses: Generate code to load the high and low parts of address constants separately. This allows GCC to optimize away redundant loads of the high order bits of addresses. This optimization requires GNU as and GNU ld. This optimization is enabled by default for some embedded targets where GNU as and GNU ld are standard.
-mrnames
-mno-rnames: The -mrnames switch says to output code using the MIPS software names for the registers, instead of the hardware names (ie, a0 instead of $4). The only known assembler that supports this option is the Algorithmics assembler.
-mgpopt
-mno-gpopt: The -mgpopt switch says to write all of the data declarations before the instructions in the text section, this allows the MIPS assembler to generate one word memory references instead of using two words for short global or static data items. This is on by default if optimization is selected.
-mstats
-mno-stats: For each non-inline function processed, the -mstats switch causes the compiler to emit one line to the standard error file to print statistics about the program (number of registers saved, stack size, etc.).
-mmemcpy
-mno-memcpy: The -mmemcpy switch makes all block moves call the appropriate string function (memcpy or bcopy) instead of possibly generating inline code.
-mmips-tfile
-mno-mips-tfile: The -mno-mips-tfile switch causes the compiler not postprocess the object file with the mips-tfile program, after the MIPS assembler has generated it to add debug support. If mips-tfile is not run, then no local variables will be available to the debugger. In addition, stage2 and stage3 objects will have the temporary file names passed to the assembler embedded in the object file, which means the objects will not compare the same. The -mno-mips-tfile switch should only be used when there are bugs in the mips-tfile program that prevents compilation.
-msoft-float: Generate output containing library calls for floating point. Warning: the requisite libraries are not part of GCC. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation.
-mhard-float: Generate output containing floating point instructions. This is the default if you use the unmodified sources.
-mabicalls
-mno-abicalls: Emit (or do not emit) the pseudo operations .abicalls, .cpload, and .cprestore that some System V.4 ports use for position independent code.
-mlong-calls
-mno-long-calls: Do all calls with the JALR instruction, which requires loading up a function's address into a register before the call. You need to use this switch, if you call outside of the current 512 megabyte segment to functions that are not through pointers.
-mhalf-pic
-mno-half-pic: Put pointers to extern references into the data section and load them up, rather than put the references in the text section.
-membedded-pic
-mno-embedded-pic: Generate PIC code suitable for some embedded systems. All calls are made using PC relative address, and all data is addressed using the $gp register. No more than 65536 bytes of global data may be used. This requires GNU as and GNU ld which do most of the work. This currently only works on targets which use ECOFF; it does not work with ELF.
-membedded-data
-mno-embedded-data: Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but reduces the amount of RAM required when executing, and thus may be preferred for some embedded systems.
-muninit-const-in-rodata
-mno-uninit-const-in-rodata: When used together with -membedded-data, it will always store uninitialized const variables in the read-only data section.
-msingle-float
-mdouble-float: The -msingle-float switch tells gcc to assume that the floating point coprocessor only supports single precision operations, as on the r4650 chip. The -mdouble-float switch permits gcc to use double precision operations. This is the default.
-mmad
-mno-mad: Permit use of the mad, madu and mul instructions, as on the r4650 chip.
-m4650: Turns on -msingle-float, -mmad, and, at least for now, -mcpu=r4650.
-mips16
-mno-mips16: Enable 16-bit instructions.
-mentry: Use the entry and exit pseudo ops. This option can only be used with -mips16.
-EL: Compile code for the processor in little endian mode. The requisite libraries are assumed to exist.
-EB: Compile code for the processor in big endian mode. The requisite libraries are assumed to exist.
-G num: Put global and static items less than or equal to num bytes into the small data or bss sections instead of the normal data or bss section. This allows the assembler to emit one word memory reference instructions based on the global pointer (gp or $28), instead of the normal two words used. By default, num is 8 when the MIPS assembler is used, and 0 when the GNU assembler is used. The -G num switch is also passed to the assembler and linker. All modules should be compiled with the same -G num value.
-nocpp: Tell the MIPS assembler to not run its preprocessor over user assembler files (with a .s suffix) when assembling them.
-mfix7000: Pass an option to gas which will cause nops to be inserted if the read of the destination register of an mfhi or mflo instruction occurs in the following two instructions.
-no-crt0: Do not include the default crt0.
-mflush-func=func
-mno-flush-func: Specifies the function to call to flush the I and D caches, or to not call any such function. If called, the function must take the same arguments as the common _flush_func(), that is, the address of the memory range for which the cache is being flushed, the size of the memory range, and the number 3 (to flush both caches). The default depends on the target gcc was configured for, but commonly is either _flush_func or __cpu_flush.

These options are defined by the macro TARGET_SWITCHES in the machine description. The default for the options is also defined by that macro, which enables you to change the defaults.