[Attributor][FIX] Only avoid visiting PHI uses multiple times (PR51249)

AAPointerInfoFloating needs to visit all uses and some multiple times if
we go through PHI nodes. Attributor::checkForAllUses keeps a visited set
so we don't recurs endlessly. We now allow recursion for non-phi uses so
we track all pointer offsets via PHI nodes properly without endless
recursion.

This replaces the first attempt D107579.

Differential Revision: https://reviews.llvm.org/D107798

llvm/lib/Transforms/IPO/Attributor.cpp

@@ -32,6 +32,7 @@
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/NoFolder.h"
 #include "llvm/IR/ValueHandle.h"
@@ -1023,7 +1024,7 @@ bool Attributor::checkForAllUses(function_ref<bool(const Use &, bool &)> Pred,
 
   while (!Worklist.empty()) {
     const Use *U = Worklist.pop_back_val();
-    if (!Visited.insert(U).second)
+    if (isa<PHINode>(U->getUser()) && !Visited.insert(U).second)
       continue;
     LLVM_DEBUG(dbgs() << "[Attributor] Check use: " << **U << " in "
                       << *U->getUser() << "\n");