https://bugs.llvm.org/show_bug.cgi?id=42300
Bug ID: 42300
Summary: [llvm-mca] How to model "result bus bubbles"?
Product: tools
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: llvm-mca
Assignee: unassignedb...@nondot.org
Reporter: lebedev...@gmail.com
CC: andrea.dibia...@gmail.com, llvm-bugs@lists.llvm.org,
matthew.da...@sony.com
"AMD Software Optimization Guide for AMD Family 10h and 12h Processors", page
250 of PDF:
"Multiplication operations always issue to integer pipe 0, and the issue logic
creates result bus bubbles for the multiplier in integer pipes 0 and 1 by
preventing non-multiply micro-ops from issuing at the appropriate time."
So in other words, as far as i understand it when "Integer Multiplier" is
occupied,
no microops may be issued to the pipe 0 and/or 1, and ALU/AGU units in those
pipes
are unoccupied.
I'm not quite sure how to model that correctly.
I did see comments for "BufferSize = 0", but i'm not sure how to limit that to
only
certain pipes/ProcResource's, since the pipe3 (it's alu/agu units) and fpu
pipes
should not be affected.
Any hints, please? :)
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