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Re: PR 6394
- From: David Edelsohn <dje at watson dot ibm dot com>
- To: Geoff Keating <geoffk at redhat dot com>
- Cc: dave at hiauly1 dot hia dot nrc dot ca, gcc at gcc dot gnu dot org
- Date: Tue, 30 Apr 2002 16:38:01 -0400
- Subject: Re: PR 6394
>>>>> Geoff Keating writes:
Geoff> Hmmm. It should have been 'GENERAL_OR_FP_REGS, pref GENERAL_REGS',
Geoff> because although FP_REGS is OK, GENERAL_REGS is cheaper (there are
Geoff> fewer moves). Perhaps a cost macro needs tweaking?
It depends how the pseudo is being used throughout its entire
lifetime. While a GPR is cheaper for the address case producing the bad
code, the pseudo may be used in an FP situation (possibly multiple times)
for which GPR is significantly more expensive.
Either generating a single pseudo was bad or, if the uses are
distinct, the register allocator should have split the lifetime across
multiple registers for the time when each register class is cheaper.
David