These command-line options are defined for RX targets:
doubledata type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in size. The default is -m32bit-doubles. Note RX floating-point hardware only works on 32-bit values, which is why the default is -m32bit-doubles.
Floating-point instructions are only generated for 32-bit floating-point values, however, so the FPU hardware is not used for doubles if the -m64bit-doubles option is used.
Note If the -fpu option is enabled then
-funsafe-math-optimizations is also enabled automatically.
This is because the RX FPU instructions are themselves unsafe.
The only difference between ‘RX600’ and ‘RX610’ is that the
‘RX610’ does not support the
The ‘RX200’ series does not have a hardware floating-point unit
and so -nofpu is enabled by default when this type is
r13) is reserved for use pointing to this area, so it is no longer available for use by the compiler. This could result in slower and/or larger code if variables are pushed onto the stack instead of being held in this register.
Note, common variables (variables that have not been initialized) and constants are not placed into the small data area as they are assigned to other sections in the output executable.
The default value is zero, which disables this feature. Note, this
feature is not enabled by default with higher optimization levels
(-O2 etc) because of the potentially detrimental effects of
reserving a register. It is up to the programmer to experiment and
discover whether this feature is of benefit to their program. See the
description of the -mpid option for a description of how the
actual register to hold the small data area pointer is chosen.
The value N can be between 0 and 4. A value of 0 (the default)
or 4 means that constants of any size are allowed.
r13is reserved for the exclusive use of fast interrupt handlers. A value of 2 reserves
r12. A value of 3 reserves
r11, and a value of 4 reserves
r10. A value of 0, the default, does not reserve any registers.
Note, using this feature reserves a register, usually
the constant data base address. This can result in slower and/or
larger code, especially in complicated functions.
The actual register chosen to hold the constant data base address
depends upon whether the -msmall-data-limit and/or the
-mint-register command-line options are enabled. Starting
r13 and proceeding downwards, registers are
allocated first to satisfy the requirements of -mint-register,
then -mpid and finally -msmall-data-limit. Thus it
is possible for the small data area register to be
r8 if both
-mint-register=4 and -mpid are specified on the
By default this feature is not enabled. The default can be restored
via the -mno-pid command-line option.
SWHILEand also the
RMPAinstruction. These instructions may prefetch data, which is not safe to do if accessing an I/O register. (See section 12.2.7 of the RX62N Group User's Manual for more information).
The default is to allow these instructions, but it is not possible for GCC to reliably detect all circumstances where a string instruction might be used to access an I/O register, so their use cannot be disabled automatically. Instead it is reliant upon the programmer to use the -mno-allow-string-insns option if their program accesses I/O space.
When the instructions are enabled GCC defines the C preprocessor
__RX_ALLOW_STRING_INSNS__, otherwise it defines the
JSRinstructions to access functions. This option can be used when code size exceeds the range of
BSRinstructions. Note that -mno-jsr does not mean to not use
JSRbut instead means that any type of branch may be used.
Note: The generic GCC command-line option -ffixed-reg
has special significance to the RX port when used with the
interrupt function attribute. This attribute indicates a
function intended to process fast interrupts. GCC ensures
that it only uses the registers
r13 and only provided that the normal use of the
corresponding registers have been restricted via the
-ffixed-reg or -mint-register command-line