[pull] master from phate:master#623
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pull[bot] merged 1 commit intoEECS-NTNU:masterfrom Jan 26, 2026
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This PR extends the existing scalar evolution analysis implementation by adding support for handling subtraction and multiplication operations. Previously, statements that included these operations were treated as unknown. More specifically, it adds cases for treating subtraction and multiplication operations. For multiplication, (two) new `SCEV` types are added, a `SCEVMulExpr` and a `SCEVNAryMulExpr`, mirroring the `SCEVAddExpr` and `SCEVNAryAddExpr` for addition operations, a new method for folding multiplication operations, `ApplyMultFolding()`, is also added. Subtraction however, does not have its own SCEV type(s), but is rather treated as an addition with the right hand-side of the expression being negated, and so it does not require as much logic to support. A new method called `GetNegativeSCEV()` is added for this purpose. In order to support different operations, we also need to keep track of which operation with which a variable depends on another (or itself). As a result, the dependency logic (necessary for invalidating certain cases and topological sorting) has been extended to include the operation as well as the number of times a variable depends on another. Currently, the implementation treats variables that have direct dependencies with multiplication (i.e. a = a * 2) as invalid, whilst other cases of multiplication that don't result in geometric sequences are OK, (e.g. a = a + b * 2). This is mainly because these are not able to be modeled as affine recurrences and because the main focus of LLVM's SCEV is linear and polynomial sequences, and these are the ones that are most relevant for optimizations like loop strength reduction and induction variable substitution.
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