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Re: Number of registers on x86
- To: dberlin at redhat dot com, dewar at gnat dot com
- Subject: Re: Number of registers on x86
- From: dewar at gnat dot com
- Date: Tue, 30 Jan 2001 00:06:02 -0500 (EST)
- Cc: gcc at gcc dot gnu dot org, tm2 at best dot com
<<Right. There is little research in the area, except to say that hardware
register renaming isn't anywhere near as efficient as doing it in the
compiler (I noticed this just scanning web pages).
It was just a thought.
Are you sure this is general wisdom. I thought the ia64 design still
had hardware renaming despite having loads of registers.
Of course the time that hardware register renanming is useful is when
there are very few hardware registers (the techniques were I think first
exploited extensively by IBM dealing with only four floating-point
registers on the mainframe architecture).
After all having a small number of hardware registers means shorter
instructions, which means lower pressure on the icache. These are all
delicately balanced tradeoffs.
In any case, this claim can be left moot, since the issue is doing a good
job on the ia32, which does make extensive use of renaming. It is not really
relevant to say that the ia32 should have more hardware registers :-)