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Re: Use-and-clobber insns and some ancient combine.c code
- From: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- To: weigand at i1 dot informatik dot uni-erlangen dot de
- Cc: gcc at gcc dot gnu dot org
- Date: Thu, 17 Jun 04 15:59:17 EDT
- Subject: Re: Use-and-clobber insns and some ancient combine.c code
When a @code{clobber} expression for a register appears inside a
@code{parallel} with other side effects, the register allocator
guarantees that the register is unoccupied both before and after that
insn. However, the reload phase may allocate a register used for one of
the inputs unless the @samp{&} constraint is specified for the selected
alternative (@pxref{Modifiers}).
These two sentences appear to directly contradict each other.
No, not at all. The first talks about the register allocator (which ignores
a '&' constraint, and the latter talks abour reload (which doesn't ignore it).