[llvm] [ConstraintElim] Support arbitrary incoming values for inductions (PR #68032)

[Nikita Popov via llvm-commits]

================
@@ -868,9 +869,10 @@ void State::addInfoForInductions(BasicBlock &BB) {
     StartValue = C->getValue();
   else if (auto *U = dyn_cast<SCEVUnknown>(StartSCEV))
     StartValue = U->getValue();
-
-  if (!StartValue)
-    return;
+  else {
+    StartValue = PN->getIncomingValueForBlock(LoopPred);
+    assert(SE.getSCEV(StartValue) == AR->getStart() && "inconsistent start value);
----------------
nikic wrote:

```suggestion
    assert(SE.getSCEV(StartValue) == StartSCEV && "inconsistent start value);
```

https://github.com/llvm/llvm-project/pull/68032