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Re: [Lightning] About 32 and 64 bits registers
From: |
Paolo Bonzini |
Subject: |
Re: [Lightning] About 32 and 64 bits registers |
Date: |
Tue, 24 Aug 2010 08:59:48 +0200 |
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On 08/24/2010 01:44 AM, Paulo César Pereira de Andrade wrote:
How is it expected to handle proper sign/zero extension when there
are no named 8/16/32/64 bit registers, that is, there is no JIT_R0c,
JIT_R0s, JIT_R0i and/or JIT_R0l.
That's on purpose, RISC machines do not have that.
This has a nasty side effect that some operations must be sign/zero
extended, for example, when loading data from a memory location. But
then, some operations become somewhat hard to explain, for example:
Loads and stores always sign/zero-extend to _l/_ul size.
jit_bltr_i LABEL, JIT_R0, IMMEDIATE
You mean jit_blti_i.
this should be understood as "treated JIT_R0 value as 32 bits, but
signed extend it, as well as immediate" ?
Yes. Instead, blti_ui would zero extend it.
But to do an "optimized" operation, it must ensure that JIT_R0 is
actually holding a 64 bits value.
Using _l operations for branches will usually give the fastest code.
jit_movi_i JIT_R0 IMMEDIATE
this should be just an alias to jit_movi_l on 64 bits, or, better
saying, should be more like:
jit_movi_i JIT_R0 (cast_to_int_32)IMMEDIATE
Yes, it should be the latter.
Paolo
- [Lightning] About 32 and 64 bits registers, Paulo César Pereira de Andrade, 2010/08/23
- Re: [Lightning] About 32 and 64 bits registers,
Paolo Bonzini <=
- Re: [Lightning] About 32 and 64 bits registers, Paulo Cesar Pereira de Andrade, 2010/08/24
- Re: [Lightning] About 32 and 64 bits registers, Paolo Bonzini, 2010/08/25
- Re: [Lightning] About 32 and 64 bits registers, Paulo César Pereira de Andrade, 2010/08/25
- Re: [Lightning] About 32 and 64 bits registers, Paolo Bonzini, 2010/08/25
- Re: [Lightning] About 32 and 64 bits registers, Paulo César Pereira de Andrade, 2010/08/25
- Re: [Lightning] About 32 and 64 bits registers, Paulo César Pereira de Andrade, 2010/08/25
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- Re: [Lightning] About 32 and 64 bits registers, Paolo Bonzini, 2010/08/29
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- Re: [Lightning] About 32 and 64 bits registers, Paolo Bonzini, 2010/08/31