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Re: Incorrect DFA scheduling of output dependency.
- From: Nathan Sidwell <nathan at codesourcery dot com>
- To: Daniel Towner <daniel dot towner at picochip dot com>
- Cc: gcc at gcc dot gnu dot org
- Date: Mon, 06 Dec 2004 12:29:51 +0000
- Subject: Re: Incorrect DFA scheduling of output dependency.
- Organization: Codesourcery LLC
- References: <41B442B7.9020408@picochip.com>
Daniel,
I am using the DFA scheduler to implement VLIW scheduling for a 16-bit
DSP. Recently I have come across an apparent bug in the scheduler.
Consider the following sequence of instructions, with DFA scheduling
turned off:
Now the DFA scheduler has grouped the four instructions into two VLIW
packets. However, the first of these packets contains an instruction
which writes to R3, and which reads from R3. Thus, the wrong value of R3
is shifted into R5. It appears that the output dependency of the initial
instruction is not being respected?
something is wrong with your scheduler description, but I know not what :)
You need to tell the scheduler about the bundling, how are you doing that?
nathan
--
Nathan Sidwell :: http://www.codesourcery.com :: CodeSourcery LLC
nathan@codesourcery.com :: http://www.planetfall.pwp.blueyonder.co.uk