3.17.38 SH Options
These `-m' options are defined for the SH implementations:
-m1- Generate code for the SH1.
-m2- Generate code for the SH2.
-m2e- Generate code for the SH2e.
-m2a-nofpu- Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way
that the floating-point unit is not used.
-m2a-single-only- Generate code for the SH2a-FPU, in such a way that no double-precision
floating-point operations are used.
-m2a-single- Generate code for the SH2a-FPU assuming the floating-point unit is in
single-precision mode by default.
-m2a- Generate code for the SH2a-FPU assuming the floating-point unit is in
double-precision mode by default.
-m3- Generate code for the SH3.
-m3e- Generate code for the SH3e.
-m4-nofpu- Generate code for the SH4 without a floating-point unit.
-m4-single-only- Generate code for the SH4 with a floating-point unit that only
supports single-precision arithmetic.
-m4-single- Generate code for the SH4 assuming the floating-point unit is in
single-precision mode by default.
-m4- Generate code for the SH4.
-m4a-nofpu- Generate code for the SH4al-dsp, or for a SH4a in such a way that the
floating-point unit is not used.
-m4a-single-only- Generate code for the SH4a, in such a way that no double-precision
floating-point operations are used.
-m4a-single- Generate code for the SH4a assuming the floating-point unit is in
single-precision mode by default.
-m4a- Generate code for the SH4a.
-m4al- Same as -m4a-nofpu, except that it implicitly passes
-dsp to the assembler. GCC doesn't generate any DSP
instructions at the moment.
-mb- Compile code for the processor in big-endian mode.
-ml- Compile code for the processor in little-endian mode.
-mdalign- Align doubles at 64-bit boundaries. Note that this changes the calling
conventions, and thus some functions from the standard C library will
not work unless you recompile it first with -mdalign.
-mrelax- Shorten some address references at link time, when possible; uses the
linker option -relax.
-mbigtable- Use 32-bit offsets in
switch tables. The default is to use
16-bit offsets.
-mbitops- Enable the use of bit manipulation instructions on SH2A.
-mfmovd- Enable the use of the instruction
fmovd. Check -mdalign for
alignment constraints.
-mhitachi- Comply with the calling conventions defined by Renesas.
-mrenesas- Comply with the calling conventions defined by Renesas.
-mno-renesas- Comply with the calling conventions defined for GCC before the Renesas
conventions were available. This option is the default for all
targets of the SH toolchain.
-mnomacsave- Mark the
MAC register as call-clobbered, even if
-mhitachi is given.
-mieee- Increase IEEE compliance of floating-point code.
At the moment, this is equivalent to -fno-finite-math-only.
When generating 16-bit SH opcodes, getting IEEE-conforming results for
comparisons of NANs / infinities incurs extra overhead in every
floating-point comparison, therefore the default is set to
-ffinite-math-only.
-minline-ic_invalidate- Inline code to invalidate instruction cache entries after setting up
nested function trampolines.
This option has no effect if -musermode is in effect and the selected
code generation option (e.g. -m4) does not allow the use of the icbi
instruction.
If the selected code generation option does not allow the use of the icbi
instruction, and -musermode is not in effect, the inlined code will
manipulate the instruction cache address array directly with an associative
write. This not only requires privileged mode, but it will also
fail if the cache line had been mapped via the TLB and has become unmapped.
-misize- Dump instruction size and location in the assembly code.
-mpadstruct- This option is deprecated. It pads structures to multiple of 4 bytes,
which is incompatible with the SH ABI.
-msoft-atomic- Generate GNU/Linux compatible gUSA software atomic sequences for the atomic
built-in functions. The generated atomic sequences require support from the
interrupt / exception handling code of the system and are only suitable for
single-core systems. They will not perform correctly on multi-core systems.
This option is enabled by default when the target is
sh-*-linux*.
For details on the atomic built-in functions see __atomic Builtins.
-mspace- Optimize for space instead of speed. Implied by -Os.
-mprefergot- When generating position-independent code, emit function calls using
the Global Offset Table instead of the Procedure Linkage Table.
-musermode- Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
if the inlined code would not work in user mode.
This is the default when the target is
sh-*-linux*.
-multcost=number- Set the cost to assume for a multiply insn.
-mdiv=strategy- Set the division strategy to use for SHmedia code. strategy must be
one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
inv:call2, inv:fp .
"fp" performs the operation in floating point. This has a very high latency,
but needs only a few instructions, so it might be a good choice if
your code has enough easily-exploitable ILP to allow the compiler to
schedule the floating-point instructions together with other instructions.
Division by zero causes a floating-point exception.
"inv" uses integer operations to calculate the inverse of the divisor,
and then multiplies the dividend with the inverse. This strategy allows
cse and hoisting of the inverse calculation. Division by zero calculates
an unspecified result, but does not trap.
"inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
have been found, or if the entire operation has been hoisted to the same
place, the last stages of the inverse calculation are intertwined with the
final multiply to reduce the overall latency, at the expense of using a few
more instructions, and thus offering fewer scheduling opportunities with
other code.
"call" calls a library function that usually implements the inv:minlat
strategy.
This gives high code density for m5-*media-nofpu compilations.
"call2" uses a different entry point of the same library function, where it
assumes that a pointer to a lookup table has already been set up, which
exposes the pointer load to cse / code hoisting optimizations.
"inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
code generation, but if the code stays unoptimized, revert to the "call",
"call2", or "fp" strategies, respectively. Note that the
potentially-trapping side effect of division by zero is carried by a
separate instruction, so it is possible that all the integer instructions
are hoisted out, but the marker for the side effect stays where it is.
A recombination to fp operations or a call is not possible in that case.
"inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
that the inverse calculation was nor separated from the multiply, they speed
up division where the dividend fits into 20 bits (plus sign where applicable),
by inserting a test to skip a number of operations in this case; this test
slows down the case of larger dividends. inv20u assumes the case of a such
a small dividend to be unlikely, and inv20l assumes it to be likely.
-maccumulate-outgoing-args- Reserve space once for outgoing arguments in the function prologue rather
than around each call. Generally beneficial for performance and size. Also
needed for unwinding to avoid changing the stack frame around conditional code.
-mdivsi3_libfunc=name- Set the name of the library function used for 32-bit signed division to
name. This only affect the name used in the call and inv:call
division strategies, and the compiler will still expect the same
sets of input/output/clobbered registers as if this option was not present.
-mfixed-range=register-range- Generate code treating the given register range as fixed registers.
A fixed register is one that the register allocator can not use. This is
useful when compiling kernel code. A register range is specified as
two registers separated by a dash. Multiple register ranges can be
specified separated by a comma.
-madjust-unroll- Throttle unrolling to avoid thrashing target registers.
This option only has an effect if the gcc code base supports the
TARGET_ADJUST_UNROLL_MAX target hook.
-mindexed-addressing- Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
This is only safe if the hardware and/or OS implement 32-bit wrap-around
semantics for the indexed addressing mode. The architecture allows the
implementation of processors with 64-bit MMU, which the OS could use to
get 32-bit addressing, but since no current hardware implementation supports
this or any other way to make the indexed addressing mode safe to use in
the 32-bit ABI, the default is -mno-indexed-addressing.
-mgettrcost=number- Set the cost assumed for the gettr instruction to number.
The default is 2 if -mpt-fixed is in effect, 100 otherwise.
-mpt-fixed- Assume pt* instructions won't trap. This will generally generate better
scheduled code, but is unsafe on current hardware. The current architecture
definition says that ptabs and ptrel trap when the target anded with 3 is 3.
This has the unintentional effect of making it unsafe to schedule ptabs /
ptrel before a branch, or hoist it out of a loop. For example,
__do_global_ctors, a part of libgcc that runs constructors at program
startup, calls functions in a list which is delimited by −1. With the
-mpt-fixed option, the ptabs will be done before testing against −1.
That means that all the constructors will be run a bit quicker, but when
the loop comes to the end of the list, the program crashes because ptabs
loads −1 into a target register. Since this option is unsafe for any
hardware implementing the current architecture specification, the default
is -mno-pt-fixed. Unless the user specifies a specific cost with
-mgettrcost, -mno-pt-fixed also implies -mgettrcost=100;
this deters register allocation using target registers for storing
ordinary integers.
-minvalid-symbols- Assume symbols might be invalid. Ordinary function symbols generated by
the compiler will always be valid to load with movi/shori/ptabs or
movi/shori/ptrel, but with assembler and/or linker tricks it is possible
to generate symbols that will cause ptabs / ptrel to trap.
This option is only meaningful when -mno-pt-fixed is in effect.
It will then prevent cross-basic-block cse, hoisting and most scheduling
of symbol loads. The default is -mno-invalid-symbols.
-mbranch-cost=num- Assume num to be the cost for a branch instruction. Higher numbers
will make the compiler try to generate more branch-free code if possible.
If not specified the value is selected depending on the processor type that
is being compiled for.
-mcbranchdi- Enable the
cbranchdi4 instruction pattern.
-mcmpeqdi- Emit the
cmpeqdi_t instruction pattern even when -mcbranchdi
is in effect.
-mfused-madd- Allow the usage of the
fmac instruction (floating-point
multiply-accumulate) if the processor type supports it. Enabling this
option might generate code that produces different numeric floating-point
results compared to strict IEEE 754 arithmetic.
-mpretend-cmove- Prefer zero-displacement conditional branches for conditional move instruction
patterns. This can result in faster code on the SH4 processor.