[clang] [llvm] [SCCP] Infer return attributes in SCCP as well (PR #106732)

[Nikita Popov via llvm-commits]

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@@ -354,6 +354,36 @@ bool SCCPSolver::removeNonFeasibleEdges(BasicBlock *BB, DomTreeUpdater &DTU,
   return true;
 }
 
+void SCCPSolver::inferReturnAttributes() const {
+  for (const auto &I : getTrackedRetVals()) {
+    Function *F = I.first;
+    const ValueLatticeElement &ReturnValue = I.second;
+
+    // If there is a known constant range for the return value, add range
+    // attribute to the return value.
+    if (ReturnValue.isConstantRange() &&
+        !ReturnValue.getConstantRange().isSingleElement()) {
+      // Do not add range metadata if the return value may include undef.
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nikic wrote:

> I don't see any tests for this.

This is pre-existing code moved to a different place.

> Is the reason for this to avoid creating UB where we where just propagating poison beforehand? If so, do you also need noundef for propagating nonnull?

`ConstantRangeIncludingUndef` means `ConstantRange|undef`. In the `undef` case any value may be picked, so the result is a full range.

https://github.com/llvm/llvm-project/pull/106732