3.18.59 Xtensa Options
These options are supported for Xtensa targets:
-mconst16-mno-const16- Enable or disable use of
CONST16 instructions for loading
constant values. The CONST16 instruction is currently not a
standard option from Tensilica. When enabled, CONST16
instructions are always used in place of the standard L32R
instructions. The use of CONST16 is enabled by default only if
the L32R 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 before
volatile memory references to guarantee sequential consistency.
The default is -mserialize-volatile. Use
-mno-serialize-volatile to omit the MEMW 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 with
MOVI instructions instead of L32R 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 like
LOOP, 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 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 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.