[llvm] [SCEV] Look thru more expressions in isKnownMultipleOf (PR #219951)

[Nikita Popov via llvm-commits]

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@@ -11285,6 +11243,26 @@ bool ScalarEvolution::isKnownMultipleOf(
   if (!Predicates)
     return false;
 
+  // Look through AddRec, Add, and Mul expressions to improve the precision of
+  // added predicates. S is a multiple of M if S starts with a multiple of M and
+  // at every iteration step S only adds multiples of M. This doesn't hold in
+  // wrapping arithmetic.
+  if (isa<SCEVAddRecExpr, SCEVAddExpr, SCEVMulExpr>(S))
+    if (cast<SCEVNAryExpr>(S)->getNoWrapFlags() != SCEV::FlagAnyWrap &&
+        all_of(S->operands(), [&](SCEVUse Op) {
+          return isKnownMultipleOf(Op, M, Predicates);
+        }))
+      return true;
+
+  // Similarly, look through MinMax to improve the precision of added
+  // predicates. There is no wrapping arithmetic to consider, as the operations
+  // just return one of its operands.
+  if (isa<SCEVMinMaxExpr>(S))
+    if (any_of(S->operands(), [&](SCEVUse Op) {
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nikic wrote:

(Should probably add alive2 proofs...)

https://github.com/llvm/llvm-project/pull/219951