[InstCombine] Improve TryToSinkInstruction with multiple uses

This patch allows sinking an instruction which can have multiple uses in a
single user. We were previously over-restrictive by looking for exactly one use,
rather than one user.

Also added an API for retrieving a unique undroppable user.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D109700

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index a13380b..0f11bf61 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -176,6 +176,18 @@ Use *Value::getSingleUndroppableUse() {
   return Result;
 }
 
+User *Value::getUniqueUndroppableUser() {
+  User *Result = nullptr;
+  for (auto *U : users()) {
+    if (!U->isDroppable()) {
+      if (Result && Result != U)
+        return nullptr;
+      Result = U;
+    }
+  }
+  return Result;
+}
+
 bool Value::hasNUndroppableUses(unsigned int N) const {
   return hasNItems(user_begin(), user_end(), N, isUnDroppableUser);
 }