[NFCI][SCEV] getPointerBase(): de-recursify

[lebedev.ri]

Summary

This is boringly straight-forward, each iteration we see if
V is some expression that we can look into, and if it has
a single pointer operand, then set V to that operand
and repeat.

[efriedma]

Do you have some plan to start using the DepthLimit somewhere?

[lebedev.ri]

In D82632#2118058, @efriedma wrote:

Do you have some plan to start using the DepthLimit somewhere?

No, i could drop it.
But it may be a good idea to consistently have such cut-offs available for use.

[efriedma]

I'd prefer not to add the cutoff until we have a real use for it.

[lebedev.ri]

In D82632#2118113, @efriedma wrote:

I'd prefer not to add the cutoff until we have a real use for it.

I see, droped it.

LG?

[nikic]

LGTM

llvm/lib/Analysis/ScalarEvolution.cpp

3970

As this is a recurring pattern, I wonder if there's room for something like llvm::get_unique(R &&Range, Getter Fn) in STLExtras.

[lebedev.ri]

In D82632#2118404, @nikic wrote:

LGTM

Thank you for the review.

llvm/lib/Analysis/ScalarEvolution.cpp

const SCEV *ScalarEvolution::getUMinFromMismatchedTypes(
   return getUMinExpr(PromotedOps);
 }
 
 const SCEV *ScalarEvolution::getPointerBase(const SCEV *V) {
   // A pointer operand may evaluate to a nonpointer expression, such as null.
   if (!V->getType()->isPointerTy())
     return V;
 
+  while (true) {
     if (const SCEVCastExpr *Cast = dyn_cast<SCEVCastExpr>(V)) {
-    return getPointerBase(Cast->getOperand());
+      V = Cast->getOperand();
     } else if (const SCEVNAryExpr *NAry = dyn_cast<SCEVNAryExpr>(V)) {
       const SCEV *PtrOp = nullptr;
       for (const SCEV *NAryOp : NAry->operands()) {
         if (NAryOp->getType()->isPointerTy()) {
-        // Cannot find the base of an expression with multiple pointer operands.
+          // Cannot find the base of an expression with multiple pointer ops.
           if (PtrOp)
             return V;
           PtrOp = NAryOp;
         }
       }
-    if (!PtrOp)
+      if (!PtrOp) // All operands were non-pointer.
         return V;
-    return getPointerBase(PtrOp);
-  }
+      V = PtrOp;
+    } else // Not something we can look further into.
       return V;
   }
+}
 
 /// Push users of the given Instruction onto the given Worklist.
 static void
 PushDefUseChildren(Instruction *I,
                    SmallVectorImpl<Instruction *> &Worklist) {
   // Push the def-use children onto the Worklist stack.
   for (User *U : I->users())
     Worklist.push_back(cast<Instruction>(U));