[llvm-bugs] [Bug 45263] New: performance regression caused by e6a7e3b5e3e779a3bfb617c8d9ed4302edab2cef

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45263

            Bug ID: 45263
           Summary: performance regression caused by
                    e6a7e3b5e3e779a3bfb617c8d9ed4302edab2cef
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: release blocker
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: wmi at google.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

We found the commit below causing 10% performance regression in one of our
benchmark:

https://github.com/llvm/llvm-project/commit/e6a7e3b5e3e779a3bfb617c8d9ed4302edab2cef

I extracted a testcase 1.cc and attached it. 

clang.1 -O3 -fexperimental-new-pass-manager -std=gnu++17 -msse4.1 1.cc -S -o
1.s

clang.2 -O3 -fexperimental-new-pass-manager -std=gnu++17 -msse4.1 1.cc -S -o
2.s

clang.1 was built at the version just before
e6a7e3b5e3e779a3bfb617c8d9ed4302edab2cef. clang.2 was built at
e6a7e3b5e3e779a3bfb617c8d9ed4302edab2cef. Searching the loop "This Inner Loop
Header: Depth=2". 1.s has 65 instructions in the loop. 2.s has 72 instructions.

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