[Value][InstCombine] Fix one-use checks in PHI-of-op -> Op-of-PHI[s] transforms to be one-user checks

As FIXME said, they really should be checking for a single user,
not use, so let's do that. It is not *that* unusual to have
the same value as incoming value in a PHI node, not unlike
how a PHI may have the same incoming basic block more than once.

There isn't a nice way to do that, Value::users() isn't uniqified,
and Value only tracks it's uses, not Users, so the check is
potentially costly since it does indeed potentially involes
traversing the entire use list of a value.

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index 26a9835..3e5dd8f 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -147,6 +147,14 @@ bool Value::hasNUsesOrMore(unsigned N) const {
   return hasNItemsOrMore(use_begin(), use_end(), N);
 }
 
+bool Value::hasOneUser() const {
+  if (use_empty())
+    return false;
+  if (hasOneUse())
+    return true;
+  return std::equal(++user_begin(), user_end(), user_begin());
+}
+
 static bool isUnDroppableUser(const User *U) { return !U->isDroppable(); }
 
 Use *Value::getSingleUndroppableUse() {