https://bugs.llvm.org/show_bug.cgi?id=48110
Bug ID: 48110
Summary: Incorrect Cost Calculations for Shuffle Ports on
Icelake-client / Icelake-server
Product: tools
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: llvm-mca
Assignee: unassignedb...@nondot.org
Reporter: dwe...@gmail.com
CC: andrea.dibia...@gmail.com, llvm-bugs@lists.llvm.org,
matthew.da...@sony.com
Hi there,
It looks like llvm-mca is treating icelake-client and icelake-server as having
only one shuffle port. This causes incorrect cost calculations for any
operation that would use said shuffle ports. A block diagram showing the
architecture can be found here:
https://en.wikichip.org/wiki/intel/microarchitectures/sunny_cove (sunny cove is
the core used by both icelake-server and icelake-client). Similarly, you can
find the uops usage for any given shuffle here:
https://uops.info/table.html?search=shuf&cb_lat=on&cb_tp=on&cb_uops=on&cb_ports=on&cb_SKL=on&cb_ICL=on&cb_measurements=on&cb_base=on&cb_avx=on
If the code generating the costs for LLVM-MCA is used by anything else in the
toolchain, it's likely this will yield a performance benefit for other users
targeting icelake-server and icelake-client.
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