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(gcc-300.info)Xtensa Options
Xtensa Options
--------------
The Xtensa architecture is designed to support many different
configurations. The compiler's default options can be set to match a
particular Xtensa configuration by copying a configuration file into the
GCC sources when building GCC. The options below may be used to
override the default options.
`-mbig-endian'
`-mlittle-endian'
Specify big-endian or little-endian byte ordering for the target
Xtensa processor.
`-mdensity'
`-mno-density'
Enable or disable use of the optional Xtensa code density
instructions.
`-mmac16'
`-mno-mac16'
Enable or disable use of the Xtensa MAC16 option. When enabled,
GCC will generate MAC16 instructions from standard C code, with the
limitation that it will use neither the MR register file nor any
instruction that operates on the MR registers. When this option is
disabled, GCC will translate 16-bit multiply/accumulate operations
to a combination of core instructions and library calls, depending
on whether any other multiplier options are enabled.
`-mmul16'
`-mno-mul16'
Enable or disable use of the 16-bit integer multiplier option.
When enabled, the compiler will generate 16-bit multiply
instructions for multiplications of 16 bits or smaller in standard
C code. When this option is disabled, the compiler will either
use 32-bit multiply or MAC16 instructions if they are available or
generate library calls to perform the multiply operations using
shifts and adds.
`-mmul32'
`-mno-mul32'
Enable or disable use of the 32-bit integer multiplier option.
When enabled, the compiler will generate 32-bit multiply
instructions for multiplications of 32 bits or smaller in standard
C code. When this option is disabled, the compiler will generate
library calls to perform the multiply operations using either
shifts and adds or 16-bit multiply instructions if they are
available.
`-mnsa'
`-mno-nsa'
Enable or disable use of the optional normalization shift amount
(`NSA') instructions to implement the built-in `ffs' function.
`-mminmax'
`-mno-minmax'
Enable or disable use of the optional minimum and maximum value
instructions.
`-msext'
`-mno-sext'
Enable or disable use of the optional sign extend (`SEXT')
instruction.
`-mbooleans'
`-mno-booleans'
Enable or disable support for the boolean register file used by
Xtensa coprocessors. This is not typically useful by itself but
may be required for other options that make use of the boolean
registers (e.g., the floating-point option).
`-mhard-float'
`-msoft-float'
Enable or disable use of the floating-point option. When enabled,
GCC generates floating-point instructions for 32-bit `float'
operations. When this option is disabled, GCC generates library
calls to emulate 32-bit floating-point operations using integer
instructions. Regardless of this option, 64-bit `double'
operations are always emulated with calls to library functions.
`-mfused-madd'
`-mno-fused-madd'
Enable or disable use of fused multiply/add and multiply/subtract
instructions in the floating-point option. This has no effect if
the floating-point option is not also enabled. Disabling fused
multiply/add and multiply/subtract instructions forces the
compiler to use separate instructions for the multiply and
add/subtract operations. This may be desirable in some cases
where strict IEEE 754-compliant results are required: the fused
multiply add/subtract instructions do not round the intermediate
result, thereby producing results with _more_ bits of precision
than specified by the IEEE standard. Disabling fused multiply
add/subtract instructions also ensures that the program output is
not sensitive to the compiler's ability to combine multiply and
add/subtract operations.
`-mserialize-volatile'
`-mno-serialize-volatile'
When this option is enabled, GCC inserts `MEMW' instructions before
`volatile' memory references to guarantee sequential consistency.
The default is `-mserialize-volatile'. Use
`-mno-serialize-volatile' to omit the `MEMW' instructions.
`-mtext-section-literals'
`-mno-text-section-literals'
Control the treatment of literal pools. The default is
`-mno-text-section-literals', which places literals in a separate
section in the output file. This allows the literal pool to be
placed in a data RAM/ROM, and it also allows the linker to combine
literal pools from separate object files to remove redundant
literals and improve code size. With `-mtext-section-literals',
the literals are interspersed in the text section in order to keep
them as close as possible to their references. This may be
necessary for large assembly files.
`-mtarget-align'
`-mno-target-align'
When this option is enabled, GCC instructs the assembler to
automatically align instructions to reduce branch penalties at the
expense of some code density. The assembler attempts to widen
density instructions to align branch targets and the instructions
following call instructions. If there are not enough preceding
safe density instructions to align a target, no widening will be
performed. The default is `-mtarget-align'. These options do not
affect the treatment of auto-aligned instructions like `LOOP',
which the assembler will always align, either by widening density
instructions or by inserting no-op instructions.
`-mlongcalls'
`-mno-longcalls'
When this option is enabled, GCC instructs the assembler to
translate direct calls to indirect calls unless it can determine
that the target of a direct call is in the range allowed by the
call instruction. This translation typically occurs for calls to
functions in other source files. Specifically, the assembler
translates a direct `CALL' instruction into an `L32R' followed by
a `CALLX' instruction. The default is `-mno-longcalls'. This
option should be used in programs where the call target can
potentially be out of range. This option is implemented in the
assembler, not the compiler, so the assembly code generated by GCC
will still show direct call instructions--look at the disassembled
object code to see the actual instructions. Note that the
assembler will use an indirect call for every cross-file call, not
just those that really will be out of range.
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