i960 Processor Compiler User's Guide
7-58
7
clobber-spec
clobber-spec
"
regname
"
Each
clobber-spec
specifies the name of a single machine register that
is "clobbered."
Resources that cannot be clobbered are:
fp (the frame pointer)
sp (the stack pointer)
r0, r1, r2 (reserved)
g14
C language object
This can be any assignable C language lvalue. Typically this is just a
variable name. A
C
language
object
must be of a type that matches its
corresponding
constraint
. A
C
language
object
used in an
output-spec
must be of a type such that it can be assigned into. Object
types must be the same size that their
constraints
would match. For
example, the C type
int is 32 bits; so is a global register. This would
cause no mismatch. An integer type would not match a quad-word,
however. If the object type and
constraint
do not match, the compiler
attempts to add code to fix the mismatch, but in general it is better practice
to avoid mismatches in the first place.
C language expression
This can be any legal C language expression. As in a
C
language
object
above, a
C
language
expression
must match its corresponding
constraint
. Unlike a
C
language
object
used in
output-specs
, a
C
language
expression
used in
input-specs
does not need to be
assignable.
constraint
Each
C
language
object
or
C
language
expression
can have an
associated
constraint
. The
constraint
is a string that tells the
compiler what its associated operand must look like in order for the
asm-template
to generate a legal assembly instruction.
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