[llvm-bugs] [Bug 47503] New: [CodeGenPrepare] Unreported IR changes in OptimizeExtractBits

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47503

            Bug ID: 47503
           Summary: [CodeGenPrepare] Unreported IR changes in
                    OptimizeExtractBits
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: dmajor at mozilla.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 23950
  --> https://bugs.llvm.org/attachment.cgi?id=23950&action=edit
OptimizeExtractBits.ll

With expensive checks enabled:
opt -codegenprepare -S OptimizeExtractBits.ll
Pass modifies its input and doesn't report it: CodeGen Prepare

The reproducer is not quite as reduced as it could be, but I need to get to a
stopping point for the week.

The `MadeChange =` should be `MadeChange |=` at
https://github.com/llvm/llvm-project/blob/06e356c81e0fce90c9a21f9f5fb7567efa51ee0f/llvm/lib/CodeGen/CodeGenPrepare.cpp#L1847

This apparently dates back to LLVM 3.5:
https://github.com/llvm/llvm-project/commit/d069f6393a7c

I haven't tested, but by inspection, this other use of `MadeChange =` also
looks suspicious:
https://github.com/llvm/llvm-project/blob/06e356c81e0fce90c9a21f9f5fb7567efa51ee0f/llvm/lib/CodeGen/CodeGenPrepare.cpp#L1153

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