On 05-Dec-01 Bruce Evans wrote:
>> - Add missing "cc" clobbers in constraints
> Does this have any effect (for i386's) except to create a lot of clutter
> Even i386.md doesn't use it. gcc.info says:
> ! If your assembler instruction can alter the condition code register,
> ! add `cc' to the list of clobbered registers. GNU CC on some machines
> ! represents the condition codes as a specific hardware register; `cc'
> ! serves to name this register. On other machines, the condition code is
> ! handled differently, and specifying `cc' has no effect. But it is
> ! valid no matter what the machine.
> ! ...
> ! Here we will concern ourselves with determining the effect of an
> ! insn on the condition code and will limit ourselves to the following
> ! possible effects: The condition code can be set unpredictably
> ! (clobbered), not be changed, be set to agree with the results of the
> ! operation, or only changed if the item previously set into the
> ! condition code has been modified.
> ! Here is part of a sample `md' file for such a machine:
> ! (define_attr "type" "load,store,arith,fp,branch" (const_string
> ! (define_attr "cc" "clobber,unchanged,set,change0"
> None of i386.md, alpha.md or sparc.md do this. i386's and alphas have a
> cc0 register, but it is only mentioned for instructsions whose main (only?)
> effect is to to set the condition codes.
Hmm, so how does one clobber "eflags" if "cc" isn't "eflags"? Look at PR
gnu/32365 which seems to indicate that "cc" does, in fact, represent "eflags"
in the clobber list.
John Baldwin <[EMAIL PROTECTED]> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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