old-cross-binutils/gas/doc/c-m32r.texi

@c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 2000, 2003
@c Free Software Foundation, Inc.
@c This is part of the GAS manual.
@c For copying conditions, see the file as.texinfo.
@ifset GENERIC
@page
@node M32R-Dependent
@chapter M32R Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter M32R Dependent Features
@end ifclear

@cindex M32R support
@menu
* M32R-Opts::                   M32R Options
* M32R-Directives::             M32R Directives
* M32R-Warnings::               M32R Warnings
@end menu

@node M32R-Opts
@section M32R Options

@cindex options, M32R
@cindex M32R options

The Renease M32R version of @code{@value{AS}} has a few machine
dependent options:

@table @code
@item -m32rx
@cindex @samp{-m32rx} option, M32RX
@cindex architecture options, M32RX
@cindex M32R architecture options
@code{@value{AS}} can assemble code for several different members of the
Renesas M32R family.  Normally the default is to assemble code for
the M32R microprocessor.  This option may be used to change the default
to the M32RX microprocessor, which adds some more instructions to the
basic M32R instruction set, and some additional parameters to some of
the original instructions.

@item -m32r
@cindex @samp{-m32r} option, M32R
@cindex architecture options, M32R
@cindex M32R architecture options
This option can be used to restore the assembler's default behaviour of
assembling for the M32R microprocessor.  This can be useful if the
default has been changed by a previous command line option.

@item -warn-explicit-parallel-conflicts
@cindex @samp{-warn-explicit-parallel-conflicts} option, M32RX
Instructs @code{@value{AS}} to produce warning messages when
questionable parallel instructions are encountered.  This option is
enabled by default, but @code{@value{GCC}} disables it when it invokes
@code{@value{AS}} directly.  Questionable instructions are those whoes
behaviour would be different if they were executed sequentially.  For
example the code fragment @samp{mv r1, r2 || mv r3, r1} produces a
different result from @samp{mv r1, r2 \n mv r3, r1} since the former
moves r1 into r3 and then r2 into r1, whereas the later moves r2 into r1
and r3.

@item -Wp
@cindex @samp{-Wp} option, M32RX
This is a shorter synonym for the @emph{-warn-explicit-parallel-conflicts}
option.

@item -no-warn-explicit-parallel-conflicts
@cindex @samp{-no-warn-explicit-parallel-conflicts} option, M32RX
Instructs @code{@value{AS}} not to produce warning messages when
questionable parallel instructions are encountered.

@item -Wnp
@cindex @samp{-Wnp} option, M32RX
This is a shorter synonym for the @emph{-no-warn-explicit-parallel-conflicts}
option.

@end table

@node M32R-Directives
@section M32R Directives
@cindex directives, M32R
@cindex M32R directives

The Renease M32R version of @code{@value{AS}} has a few architecture
specific directives:

@table @code
@cindex @code{.low} directive, M32R
@item .low @var{expression}
The @code{.low} directive computes the value of its expression and
places the lower 16-bits of the result into the immediate-field of the
instruction.  For example:

@smallexample
   or3   r0, r0, #low(0x12345678) ; compute r0 = r0 | 0x5678 
   add3, r0, r0, #low(fred)   ; compute r0 = r0 + low 16-bits of address of fred
@end smallexample

@item .high @var{expression}
@cindex @code{.high} directive, M32R
The @code{.high} directive computes the value of its expression and
places the upper 16-bits of the result into the immediate-field of the
instruction.  For example:

@smallexample
   seth  r0, #high(0x12345678) ; compute r0 = 0x12340000 
   seth, r0, #high(fred)       ; compute r0 = upper 16-bits of address of fred
@end smallexample

@item .shigh @var{expression}
@cindex @code{.shigh} directive, M32R
The @code{.shigh} directive is very similar to the @code{.high}
directive.  It also computes the value of its expression and places
the upper 16-bits of the result into the immediate-field of the 
instruction.  The difference is that @code{.shigh} also checks to see
if the lower 16-bits could be interpreted as a signed number, and if
so it assumes that a borrow will occur from the upper-16 bits.  To
compensate for this the @code{.shigh} directive pre-biases the upper
16 bit value by adding one to it.  For example:

For example:

@smallexample
   seth  r0, #shigh(0x12345678) ; compute r0 = 0x12340000
   seth  r0, #shigh(0x00008000) ; compute r0 = 0x00010000
@end smallexample

In the second example the lower 16-bits are 0x8000.  If these are
treated as a signed value and sign extended to 32-bits then the value
becomes 0xffff8000.  If this value is then added to 0x00010000 then
the result is 0x00008000.

This behaviour is to allow for the different semantics of the
@code{or3} and @code{add3} instructions.  The @code{or3} instruction
treats its 16-bit immediate argument as unsigned whereas the
@code{add3} treats its 16-bit immediate as a signed value.  So for
example:

@smallexample
   seth  r0, #shigh(0x00008000) 
   add3  r0, r0, #low(0x00008000) 
@end smallexample

Produces the correct result in r0, whereas:

@smallexample
   seth  r0, #shigh(0x00008000) 
   or3   r0, r0, #low(0x00008000) 
@end smallexample

Stores 0xffff8000 into r0.

Note - the @code{shigh} directive does not know where in the assembly
source code the lower 16-bits of the value are going set, so it cannot
check to make sure that an @code{or3} instruction is being used rather
than an @code{add3} instruction.  It is up to the programmer to make
sure that correct directives are used.
@end table

@node M32R-Warnings
@section M32R Warnings

@cindex warnings, M32R
@cindex M32R warnings

There are several warning and error messages that can be produced by
@code{@value{AS}} which are specific to the M32R:

@table @code

@item output of 1st instruction is the same as an input to 2nd instruction - is this intentional ?
This message is only produced if warnings for explicit parallel
conflicts have been enabled.  It indicates that the assembler has
encountered a parallel instruction in which the destination register of
the left hand instruction is used as an input register in the right hand
instruction.  For example in this code fragment
@samp{mv r1, r2 || neg r3, r1} register r1 is the destination of the
move instruction and the input to the neg instruction.

@item output of 2nd instruction is the same as an input to 1st instruction - is this intentional ?
This message is only produced if warnings for explicit parallel
conflicts have been enabled.  It indicates that the assembler has
encountered a parallel instruction in which the destination register of
the right hand instruction is used as an input register in the left hand
instruction.  For example in this code fragment
@samp{mv r1, r2 || neg r2, r3} register r2 is the destination of the
neg instruction and the input to the move instruction.

@item instruction @samp{...} is for the M32RX only
This message is produced when the assembler encounters an instruction
which is only supported by the M32Rx processor, and the @samp{-m32rx}
command line flag has not been specified to allow assembly of such
instructions. 

@item unknown instruction @samp{...}
This message is produced when the assembler encounters an instruction
which it does not recognise.

@item only the NOP instruction can be issued in parallel on the m32r
This message is produced when the assembler encounters a parallel
instruction which does not involve a NOP instruction and the
@samp{-m32rx} command line flag has not been specified.  Only the M32Rx
processor is able to execute two instructions in parallel.

@item instruction @samp{...} cannot be executed in parallel.
This message is produced when the assembler encounters a parallel
instruction which is made up of one or two instructions which cannot be
executed in parallel.

@item Instructions share the same execution pipeline
This message is produced when the assembler encounters a parallel
instruction whoes components both use the same execution pipeline.

@item Instructions write to the same destination register.
This message is produced when the assembler encounters a parallel
instruction where both components attempt to modify the same register.
For example these code fragments will produce this message:
@samp{mv r1, r2 || neg r1, r3}
@samp{jl r0 || mv r14, r1}
@samp{st r2, @@-r1 || mv r1, r3} 
@samp{mv r1, r2 || ld r0, @@r1+} 
@samp{cmp r1, r2 || addx r3, r4} (Both write to the condition bit)

@end table