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* tm.texi (SMALL_REGISTER_CLASSES): Make description match reality.

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From-SVN: r24092
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Bernd Schmidt 1998-12-04 13:09:39 +00:00 committed by Bernd Schmidt
parent 4dab1f3e9f
commit faa9eb1977
2 changed files with 8 additions and 8 deletions
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gcc/ChangeLog
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@ -1,5 +1,7 @@
Fri Dec 4 20:15:57 1998 Bernd Schmidt <crux@pool.informatik.rwth-aachen.de>
* tm.texi (SMALL_REGISTER_CLASSES): Make description match reality.
* final.c (cleanup_subreg_operands): Delete some unused code.
* recog.h (MAX_RECOG_ALTERNATIVES): New macro.

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gcc/tm.texi
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@ -2022,17 +2022,15 @@ is @code{BITS_PER_WORD} bits wide is correct for your machine.
@findex SMALL_REGISTER_CLASSES
@item SMALL_REGISTER_CLASSES
Normally the compiler avoids choosing registers that have been
explicitly mentioned in the rtl as spill registers (these registers are
normally those used to pass parameters and return values). However,
some machines have so few registers of certain classes that there
would not be enough registers to use as spill registers if this were
done.
On some machines, it is risky to let hard registers live across arbitrary
insns. Typically, these machines have instructions that require values
to be in specific registers (like an accumulator), and reload will fail
if the required hard register is used for another purpose across such an
insn.
Define @code{SMALL_REGISTER_CLASSES} to be an expression with a non-zero
value on these machines. When this macro has a non-zero value, the
compiler allows registers explicitly used in the rtl to be used as spill
registers but avoids extending the lifetime of these registers.
compiler will try to minimize the lifetime of hard registers.
It is always safe to define this macro with a non-zero value, but if you
unnecessarily define it, you will reduce the amount of optimizations