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Re: negative latencies
- From: shmeel gutl <shmeelgutl at shmuelhome dot mine dot nu>
- To: Vladimir Makarov <vmakarov at redhat dot com>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Fri, 23 May 2014 10:49:47 +0300
- Subject: Re: negative latencies
- Authentication-results: sourceware.org; auth=none
- References: <5379A125 dot 5090405 at shmuelhome dot mine dot nu> <537B7121 dot 6080408 at redhat dot com> <537BC690 dot 2030807 at shmuelhome dot mine dot nu> <537CC6A8 dot 6090607 at redhat dot com>
On 21-May-14 06:30 PM, Vladimir Makarov wrote:
This is not a problem for this architecture. The units are fully
pipelined and the only conflicts are in the first stage, during
instruction issue. That is, the vliw must be legal. The gcc dfa handles
this case fine.
I am just curious what happens when you put
and insn2 uses a result of insn1 in 6 cycles and insn1 producing the
result in 3 cycles, but there are not ready functional units (e.g.
arithmentic units) necessary for insn1 for 4 or more cycles. It is
quite not trivial to guarantee that everything will be okay in general
case if you put insn2 before insn1.