Xtensa Options#
These options are supported for Xtensa targets:
- -mconst16, -mno-const16#
Enable or disable use of
CONST16
instructions for loading constant values. TheCONST16
instruction is currently not a standard option from Tensilica. When enabled,CONST16
instructions are always used in place of the standardL32R
instructions. The use ofCONST16
is enabled by default only if theL32R
instruction is not available.
- -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 beforevolatile
memory references to guarantee sequential consistency. The default is-mserialize-volatile
. Use-mno-serialize-volatile
to omit theMEMW
instructions.
- -mforce-no-pic#
For targets, like GNU/Linux, where all user-mode Xtensa code must be position-independent code (PIC), this option disables PIC for compiling kernel code.
- -mtext-section-literals, -mno-text-section-literals#
These options 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. Literals for each function are placed right before that function.
- -mauto-litpools, -mno-auto-litpools#
These options control the treatment of literal pools. The default is
-mno-auto-litpools
, which places literals in a separate section in the output file unless-mtext-section-literals
is used. With-mauto-litpools
the literals are interspersed in the text section by the assembler. Compiler does not produce explicit.literal
directives and loads literals into registers withMOVI
instructions instead ofL32R
to let the assembler do relaxation and place literals as necessary. This option allows assembler to create several literal pools per function and assemble very big functions, which may not be possible with-mtext-section-literals
.
- -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 is performed. The default is
-mtarget-align
. These options do not affect the treatment of auto-aligned instructions likeLOOP
, which the assembler always aligns, either by widening density instructions or by inserting NOP 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 anL32R
followed by aCALLX
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 still shows direct call instructions—look at the disassembled object code to see the actual instructions. Note that the assembler uses an indirect call for every cross-file call, not just those that really are out of range.
- -mabi=name#
Generate code for the specified ABI. Permissible values are:
call0
,windowed
. Default ABI is chosen by the Xtensa core configuration.
- -mabi=call0#
When this option is enabled function parameters are passed in registers
a2
througha7
, registersa12
througha15
are caller-saved, and registera15
may be used as a frame pointer. When this version of the ABI is enabled the C preprocessor symbol__XTENSA_CALL0_ABI__
is defined.
- -mabi=windowed#
When this option is enabled function parameters are passed in registers
a10
througha15
, and called function rotates register window by 8 registers on entry so that its arguments are found in registersa2
througha7
. Registera7
may be used as a frame pointer. Register window is rotated 8 registers back upon return. When this version of the ABI is enabled the C preprocessor symbol__XTENSA_WINDOWED_ABI__
is defined.
- -mextra-l32r-costs=n#
Specify an extra cost of instruction RAM/ROM access for
L32R
instructions, in clock cycles. This affects, when optimizing for speed, whether loading a constant from literal pool usingL32R
or synthesizing the constant from a small one with a couple of arithmetic instructions. The default value is 0.