MIPS2(5) MIPS2(5)
mips2 - MIPS2 architecture extensions and the -mips2 compiler option
cc -mips2 [ options ] ... file ...
f77 -mips2 [ options ] ... file ...
pc -mips2 [ options ] ... file ...
as -mips2 [ options ] ... file ...
The MIPS R4000 processor contains many instruction set extensions to the
MIPS1 instruction set that was defined by the MIPS R2000/R3000. A subset
of these instruction set extensions defines the MIPS2 instruction set and
is accessible with the -mips2 option. The MIPS3 instruction set includes
the remaining extensions and is described in mips3(5).
The -mips2 option is supported when compiling C, C++, Fortran, Pascal or
Assembly language source files. It instructs the code generation phase to
generate the MIPS2 instructions wherever beneficial. The option also
causes the instruction scheduler phase to use the R4000 processor model
while scheduling instructions. When linking, the -mips2 option instructs
the linker ld(1) to use MIPS2 specific versions of libraries from the
directory /usr/lib/mips2.
The new features added by the MIPS2 instruction set extensions are:
o Double precision floating point load and store instructions. This
can provide significant improvement to code using double precision
floating point manipulation. A single instruction can load/store a
double precision floating point value. In contrast, the R2000/R3000
required using two instructions to reference the upper half and the
lower half of the double precision value.
o Intrinsic instructions to convert floating point numbers. The new
instructions provide truncate, round, ceiling and floor operations.
On the R2000/R3000, these instructions were implemented as assembler
macros which expanded into approximately 11 instructions. Code which
does significant amount of floating point to integer conversions
should benefit from the -mips2 option.
o Floating point sqrt instruction. This is faster than the sqrt
routine in the math libraries for the R2000/R3000.
o Branch likely instructions. Every branch instruction in the MIPS1
architecture has a corresponding branch likely form. In this form of
the branch, the instruction in the delay slot of the branch is
nullified if the conditional branch is not taken.
o New compare and trap instructions, which cause an exception to be
raised based on the result of comparing two registers or a register
and immediate value. In the R2000/R3000, these instructions were
implemented as assembler macros which expanded into a sequence using
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MIPS2(5) MIPS2(5)
a conditional branch and a break instruction.
A special set of libraries compiled with the -mips2 option and making use
of MIPS2 features is provided in the /usr/lib/mips2 directory. As part of
the basic development environment you get MIPS2 versions of libfastm.a,
libm.a and libm43.a libraries. As part of the Fortran compiler you get
MIPS2 versions of libF77.a, libI77.a, libU77.a and libisam.a . The
shared library versions of the above Fortran libraries do not currently
have a MIPS2 version.
Code compiled and/or linked using the -mips2 option will not run on
R2000/R3000 based machines. Code compiled without the -mips2 option will
run on all machines -- R2000/R3000/R4000 -- within the constraints of
operating system compatibility. If broad machine base compatibility is an
issue, SGI recommends using the -mips2 option only when significant
benefit is achieved on an R4000 based system as compared to running the
same program compiled without the -mips2 option on the same R4000 based
system.
The double precision floating point load and store instructions require
the data to be aligned on a double word boundary. A non-aligned access
will cause the program to abort with a "bus error" message. This
requirement may cause some programs that worked fine earlier, to fail
when recompiled with the -mips2 option. This can happen in some Fortran
programs that have common blocks with an odd number of integer values
followed by double precision data.
Assembly Language Programmer's Guide
MIPS RISC Architecture, Gerry Kane and Joe Heinrich, Prentice Hall.
MIPS R4000 User's Manual, Joseph Heinrich, Prentice Hall.
cc(1), f77(1), pc(1), CC(1), as(1), mips3(5)
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