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Re: [PATCH] Fix scheduling undeterminism from sorting with DEBUG_INSNs

From: Jeff Law <law at redhat dot com>
To: Maxim Kuvyrkov <maxim dot kuvyrkov at linaro dot org>, GCC Patches <gcc-patches at gcc dot gnu dot org>
Cc: Ramana Radhakrishnan <ramana dot radhakrishnan at arm dot com>, Vladimir Makarov <vmakarov at redhat dot com>
Date: Thu, 22 Jan 2015 10:11:35 -0700
Subject: Re: [PATCH] Fix scheduling undeterminism from sorting with DEBUG_INSNs
Authentication-results: sourceware.org; auth=none
References: <1C9D1942-81E0-4245-BC86-CC8F191956F2 at linaro dot org>

On 01/19/15 06:07, Maxim Kuvyrkov wrote:


The underlying problem is that the order in which elements of
ready_list are compared matters to the final result.  This is because
rank_for_schedule sorting heuristic establishes a partial order on
the set of instructions, and it can happen that with 3 instructions
A, B and C: A>B, B>C, C>A.  In this situation the order in which
qsort compares the elements affects the final result, it can be
either ABC or BCA or CAB.

So how precisely do we get A > B, B > C and C > A? Unless I'm missingsomething, that seems to be an extremely bad result from rank_for_schedule.


Jeff

Follow-Ups:
- Re: [PATCH] Fix scheduling undeterminism from sorting with DEBUG_INSNs
  - From: Maxim Kuvyrkov

References:
- [PATCH] Fix scheduling undeterminism from sorting with DEBUG_INSNs
  - From: Maxim Kuvyrkov

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