From 01a26ffc1abeabbeaf77c93f3ac9af1bd75cc710 Mon Sep 17 00:00:00 2001
From: Daniel Berlin <dberlin@dberlin.org>
Date: Wed, 30 Aug 2017 19:52:39 +0000
Subject: [PATCH] NewGVN: Allow simplification into variables

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312161 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/NewGVN.cpp | 43 ++++++++++++++++----------------
 1 file changed, 21 insertions(+), 22 deletions(-)

diff --git a/lib/Transforms/Scalar/NewGVN.cpp b/lib/Transforms/Scalar/NewGVN.cpp
index 40e671fc108..ababf7f76e3 100644
--- a/lib/Transforms/Scalar/NewGVN.cpp
+++ b/lib/Transforms/Scalar/NewGVN.cpp
@@ -938,8 +938,6 @@ const Expression *NewGVN::createBinaryExpression(unsigned Opcode, Type *T,
 // Take a Value returned by simplification of Expression E/Instruction
 // I, and see if it resulted in a simpler expression. If so, return
 // that expression.
-// TODO: Once finished, this should not take an Instruction, we only
-// use it for printing.
 const Expression *NewGVN::checkSimplificationResults(Expression *E,
                                                      Instruction *I,
                                                      Value *V) const {
@@ -963,22 +961,30 @@ const Expression *NewGVN::checkSimplificationResults(Expression *E,
   }
 
   CongruenceClass *CC = ValueToClass.lookup(V);
-  if (CC && CC->getDefiningExpr()) {
-    // If we simplified to something else, we need to communicate
-    // that we're users of the value we simplified to.
-    if (I != V) {
-      // Don't add temporary instructions to the user lists.
-      if (!AllTempInstructions.count(I))
-        addAdditionalUsers(V, I);
+  if (CC) {
+    if (CC->getLeader() && CC->getLeader() != I) {
+      addAdditionalUsers(V, I);
+      return createVariableOrConstant(CC->getLeader());
     }
 
-    if (I)
-      DEBUG(dbgs() << "Simplified " << *I << " to "
-                   << " expression " << *CC->getDefiningExpr() << "\n");
-    NumGVNOpsSimplified++;
-    deleteExpression(E);
-    return CC->getDefiningExpr();
+    if (CC->getDefiningExpr()) {
+      // If we simplified to something else, we need to communicate
+      // that we're users of the value we simplified to.
+      if (I != V) {
+        // Don't add temporary instructions to the user lists.
+        if (!AllTempInstructions.count(I))
+          addAdditionalUsers(V, I);
+      }
+
+      if (I)
+        DEBUG(dbgs() << "Simplified " << *I << " to "
+                     << " expression " << *CC->getDefiningExpr() << "\n");
+      NumGVNOpsSimplified++;
+      deleteExpression(E);
+      return CC->getDefiningExpr();
+    }
   }
+
   return nullptr;
 }
 
@@ -998,13 +1004,6 @@ const Expression *NewGVN::createExpression(Instruction *I) const {
   }
 
   // Perform simplification.
-  // TODO: Right now we only check to see if we get a constant result.
-  // We may get a less than constant, but still better, result for
-  // some operations.
-  // IE
-  //  add 0, x -> x
-  //  and x, x -> x
-  // We should handle this by simply rewriting the expression.
   if (auto *CI = dyn_cast<CmpInst>(I)) {
     // Sort the operand value numbers so x<y and y>x get the same value
     // number.
-- 
2.50.1