IROutliner: Use ValueMapper to remap constants in a function

Stop relying on the uselist of constants, which also required filtering
the uses that are in the correct function. I'm not sure why this pass is
doing its own cloning instead of building the value map while doing its
cloning.

Author: arsenm

llvm/lib/Transforms/IPO/IROutliner.cpp

@@ -24,6 +24,7 @@
 #include "llvm/IR/PassManager.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Transforms/IPO.h"
+#include "llvm/Transforms/Utils/ValueMapper.h"
 #include <optional>
 #include <vector>
 
@@ -1930,10 +1931,12 @@ replaceArgumentUses(OutlinableRegion &Region,
 /// \param Region [in] - The region of extracted code to be changed.
 void replaceConstants(OutlinableRegion &Region) {
   OutlinableGroup &Group = *Region.Parent;
+  Function *OutlinedFunction = Group.OutlinedFunction;
+  ValueToValueMapTy VMap;
+
   // Iterate over the constants that need to be elevated into arguments
   for (std::pair<unsigned, Constant *> &Const : Region.AggArgToConstant) {
     unsigned AggArgIdx = Const.first;
-    Function *OutlinedFunction = Group.OutlinedFunction;
     assert(OutlinedFunction && "Overall Function is not defined?");
     Constant *CST = Const.second;
     Argument *Arg = Group.OutlinedFunction->getArg(AggArgIdx);
@@ -1943,16 +1946,14 @@ void replaceConstants(OutlinableRegion &Region) {
     // TODO: If in the future constants do not have one global value number,
     // i.e. a constant 1 could be mapped to several values, this check will
     // have to be more strict.  It cannot be using only replaceUsesWithIf.
-
+    VMap[CST] = Arg;
     LLVM_DEBUG(dbgs() << "Replacing uses of constant " << *CST
                       << " in function " << *OutlinedFunction << " with "
-                      << *Arg << "\n");
-    CST->replaceUsesWithIf(Arg, [OutlinedFunction](Use &U) {
-      if (Instruction *I = dyn_cast<Instruction>(U.getUser()))
-        return I->getFunction() == OutlinedFunction;
-      return false;
-    });
+                      << *Arg << '\n');
   }
+
+  RemapFunction(*OutlinedFunction, VMap,
+                RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
 }
 
 /// It is possible that there is a basic block that already performs the same