[IR] Allow Value::replaceUsesWithIf() to process constants

The change is currently NFC, but exploited by the depending D102954.
Code to handle constants is borrowed from the general implementation
of Value::doRAUW().

Differential Revision: https://reviews.llvm.org/D103051

include/llvm/IR/Value.h

@@ -311,27 +311,15 @@ public:
   /// Go through the uses list for this definition and make each use point
   /// to "V" if the callback ShouldReplace returns true for the given Use.
   /// Unlike replaceAllUsesWith() this function does not support basic block
-  /// values or constant users.
+  /// values.
   void replaceUsesWithIf(Value *New,
-                         llvm::function_ref<bool(Use &U)> ShouldReplace) {
-    assert(New && "Value::replaceUsesWithIf(<null>) is invalid!");
-    assert(New->getType() == getType() &&
-           "replaceUses of value with new value of different type!");
-
-    for (use_iterator UI = use_begin(), E = use_end(); UI != E;) {
-      Use &U = *UI;
-      ++UI;
-      if (!ShouldReplace(U))
-        continue;
-      U.set(New);
-    }
-  }
+                         llvm::function_ref<bool(Use &U)> ShouldReplace);
 
   /// replaceUsesOutsideBlock - Go through the uses list for this definition and
   /// make each use point to "V" instead of "this" when the use is outside the
   /// block. 'This's use list is expected to have at least one element.
   /// Unlike replaceAllUsesWith() this function does not support basic block
-  /// values or constant users.
+  /// values.
   void replaceUsesOutsideBlock(Value *V, BasicBlock *BB);
 
   //----------------------------------------------------------------------

lib/IR/Value.cpp

@@ -532,6 +532,29 @@ void Value::replaceNonMetadataUsesWith(Value *New) {
   doRAUW(New, ReplaceMetadataUses::No);
 }
 
+void Value::replaceUsesWithIf(Value *New,
+                              llvm::function_ref<bool(Use &U)> ShouldReplace) {
+  assert(New && "Value::replaceUsesWithIf(<null>) is invalid!");
+  assert(New->getType() == getType() &&
+         "replaceUses of value with new value of different type!");
+
+  for (use_iterator UI = use_begin(), E = use_end(); UI != E;) {
+    Use &U = *UI;
+    ++UI;
+    if (!ShouldReplace(U))
+      continue;
+    // Must handle Constants specially, we cannot call replaceUsesOfWith on a
+    // constant because they are uniqued.
+    if (auto *C = dyn_cast<Constant>(U.getUser())) {
+      if (!isa<GlobalValue>(C)) {
+        C->handleOperandChange(this, New);
+        continue;
+      }
+    }
+    U.set(New);
+  }
+}
+
 /// Replace llvm.dbg.* uses of MetadataAsValue(ValueAsMetadata(V)) outside BB
 /// with New.
 static void replaceDbgUsesOutsideBlock(Value *V, Value *New, BasicBlock *BB) {