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This PR is related to #99591. In this PR, instead of modifying how the legalisation occurs depending on surrounding instructions, we refine after legalisation. This PR has two parts: * `SDPatternMatch/MatchContext`: Modify a little bit the code to match Operands (used by `m_Node(...)`) and Unary/Binary/Ternary Patterns to make it compatible with `VPMatchContext`, instead of only `m_Opc` supported. Some tests were added to ensure no regressions. * `DAGCombiner`: Add a `foldSubCtlzNot` which detect and rewrite the patterns using matching context. Remaining Tasks: - [ ] GlobalISel - [ ] Currently the pattern matching will occur even before legalisation. Should I restrict it to specific stages instead ? - [ ] Style: Add a visitVP_SUB ?? Move `foldSubCtlzNot` in another location for style consistency purpose ? @topperc --------- Co-authored-by: v01dxyz <v01dxyz@v01d.xyz>