[llvm-bugs] [Bug 51817] New: [SCEV] Violation of proposed definitional flag rules

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https://bugs.llvm.org/show_bug.cgi?id=51817

            Bug ID: 51817
           Summary: [SCEV] Violation of proposed definitional flag rules
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: listmail at philipreames.com
                CC: llvm-bugs at lists.llvm.org

This bug exists to track known violations of the proposed nowrap flag semantics
for SCEV in https://reviews.llvm.org/D109553.  If that proposal is accepted,
this becomes a punch list.  If it isn't, it will be closed as invalid.

Issues known at time of filing
* When folding loop invariant terms into an AddRec's start (in getAddExpr), we
propagate flag valid in the defining scope of the AddRec outside of it.  This
is D106852.
* In applyLoopGuards, we apply contextual flags when reasoning about the
replacement given a urem expression.  Removing this causes no test diffs.
* In getGEPExpr, we blindly copy flags from the IR gep (if inbounds) to the
corresponding MulExprs and AddExpr.  This creates a set of SCEVs with
non-definitional flags.  As noted in the fixme, we should be using similar
logic to AddRecNeverPoison here.

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