[llvm-bugs] [Bug 36671] New: [llvm-mca][x86] Teach how to identify optimizable register-register moves and zero-idioms.

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Mar 9 07:51:44 PST 2018


https://bugs.llvm.org/show_bug.cgi?id=36671

            Bug ID: 36671
           Summary: [llvm-mca][x86] Teach how to identify optimizable
                    register-register moves and zero-idioms.
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: andrea.dibiagio at gmail.com
                CC: llvm-bugs at lists.llvm.org

This is currently marked as x86. However, it may apply to other targets other
than x86.

Most modern Intel/AMD processors know how to eliminate register-register moves
and zero idioms at register renaming stage. The tool currently doesn't know
about these patterns, and this may negatively impact the performance analysis.

We want to expose this information to llvm-mca. Ideally, the tool should have a
View to generate performance counters for the:
 - number of register moves eliminated
 - number of zero idioms eliminated

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