[ARM] Fix non-determenistic behaviour

Summary:
ARM Type Promotion pass does not clear
the container that defines if one variable
was visited or not, missing optimization
opportunities by luck when two llvm:Values
from different functions  are allocated at
the same memory address.

Also fixes a comment and uses existing
method to pop and obtain last element
of the worklist.

Reviewers: samparker

Reviewed By: samparker

Subscribers: kristof.beyls, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73970

lib/CodeGen/TypePromotion.cpp

@@ -847,8 +847,7 @@ bool TypePromotion::TryToPromote(Value *V, unsigned PromotedWidth) {
 
   // Iterate through, and add to, a tree of operands and users in the use-def.
   while (!WorkList.empty()) {
-    Value *V = WorkList.back();
-    WorkList.pop_back();
+    Value *V = WorkList.pop_back_val();
     if (CurrentVisited.count(V))
       continue;
 
@@ -917,7 +916,7 @@ bool TypePromotion::TryToPromote(Value *V, unsigned PromotedWidth) {
      ++ToPromote;
    }
 
-  // DAG optimisations should be able to handle these cases better, especially
+  // DAG optimizations should be able to handle these cases better, especially
   // for function arguments.
   if (ToPromote < 2 || (Blocks.size() == 1 && (NonFreeArgs > SafeWrap.size())))
     return false;
@@ -941,6 +940,9 @@ bool TypePromotion::runOnFunction(Function &F) {
   if (!TPC)
     return false;
 
+  AllVisited.clear();
+  SafeToPromote.clear();
+  SafeWrap.clear();
   bool MadeChange = false;
   const DataLayout &DL = F.getParent()->getDataLayout();
   const TargetMachine &TM = TPC->getTM<TargetMachine>();
@@ -998,6 +1000,10 @@ bool TypePromotion::runOnFunction(Function &F) {
   if (MadeChange)
     LLVM_DEBUG(dbgs() << "After TypePromotion: " << F << "\n");
 
+  AllVisited.clear();
+  SafeToPromote.clear();
+  SafeWrap.clear();
+
   return MadeChange;
 }