[llvm] [SCEV] Unify and optimize constant folding (NFC) (PR #101473)

[Nikita Popov via llvm-commits]

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@@ -831,6 +831,49 @@ static bool hasHugeExpression(ArrayRef<const SCEV *> Ops) {
   });
 }
 
+/// Performs a number of common optimizations on the passed \p Ops. If the
+/// whole expression reduces down to a single operand, it will be returned.
+///
+/// The following optimizations are performed:
+///  * Fold constants using the \p Fold function.
+///  * Remove identity constants satisfying \p IsIdentity.
+///  * If a constant satisfies \p IsAbsorber, return it.
+///  * Sort operands by complexity.
+template <typename FoldT, typename IsIdentityT, typename IsAbsorberT>
+static const SCEV *
+constantFoldAndGroupOps(ScalarEvolution &SE, LoopInfo &LI, DominatorTree &DT,
+                        SmallVectorImpl<const SCEV *> &Ops, FoldT Fold,
+                        IsIdentityT IsIdentity, IsAbsorberT IsAbsorber) {
+  const SCEVConstant *Folded = nullptr;
+  for (unsigned Idx = 0; Idx < Ops.size();) {
+    const SCEV *Op = Ops[Idx];
+    if (const auto *C = dyn_cast<SCEVConstant>(Op)) {
+      if (!Folded)
+        Folded = C;
+      else
+        Folded = cast<SCEVConstant>(
+            SE.getConstant(Fold(Folded->getAPInt(), C->getAPInt())));
+      Ops.erase(Ops.begin() + Idx);
+      continue;
+    }
+    ++Idx;
+  }
+
+  if (Ops.empty()) {
+    assert(Folded && "Must have folded value");
+    return Folded;
+  }
+
+  if (Folded && IsAbsorber(Folded->getAPInt()))
+    return Folded;
+
+  GroupByComplexity(Ops, &LI, DT);
+  if (Folded && !IsIdentity(Folded->getAPInt()))
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nikic wrote:

I'll investigate whether this is better this in a followup.

https://github.com/llvm/llvm-project/pull/101473