From 3f5fd1b1290277c6ff5c0e035b53e2b0f37a038b Mon Sep 17 00:00:00 2001
From: Michael Zolotukhin <mzolotukhin@apple.com>
Date: Tue, 17 Apr 2018 04:45:22 +0000
Subject: [PATCH] Reapply "[PR16756] Use SSAUpdaterBulk in JumpThreading."
 again.

One more, hopefully the last, bug is fixed: when forming UsesToRewrite
we should ignore phi operands coming from edges that we want to delete.

This reverts r329910.

llvm-svn: 330175
---
 llvm/lib/Transforms/Scalar/JumpThreading.cpp      | 37 ++++++++++++++---------
 llvm/test/Transforms/JumpThreading/removed-use.ll | 28 +++++++++++++++++
 2 files changed, 50 insertions(+), 15 deletions(-)
 create mode 100644 llvm/test/Transforms/JumpThreading/removed-use.ll

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 29c7077..85d2c32 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -66,6 +66,7 @@
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include "llvm/Transforms/Utils/SSAUpdater.h"
+#include "llvm/Transforms/Utils/SSAUpdaterBulk.h"
 #include "llvm/Transforms/Utils/ValueMapper.h"
 #include <algorithm>
 #include <cassert>
@@ -1989,15 +1990,21 @@ bool JumpThreadingPass::ThreadEdge(BasicBlock *BB,
   // now have to update all uses of the value to use either the original value,
   // the cloned value, or some PHI derived value.  This can require arbitrary
   // PHI insertion, of which we are prepared to do, clean these up now.
-  SSAUpdater SSAUpdate;
+  SSAUpdaterBulk SSAUpdate;
   SmallVector<Use*, 16> UsesToRename;
+
+  unsigned VarNum = 0;
   for (Instruction &I : *BB) {
+    UsesToRename.clear();
+
     // Scan all uses of this instruction to see if it is used outside of its
-    // block, and if so, record them in UsesToRename.
+    // block, and if so, record them in UsesToRename. Also, skip phi operands
+    // from PredBB - we'll remove them anyway.
     for (Use &U : I.uses()) {
       Instruction *User = cast<Instruction>(U.getUser());
       if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
-        if (UserPN->getIncomingBlock(U) == BB)
+        if (UserPN->getIncomingBlock(U) == BB ||
+            UserPN->getIncomingBlock(U) == PredBB)
           continue;
       } else if (User->getParent() == BB)
         continue;
@@ -2008,19 +2015,15 @@ bool JumpThreadingPass::ThreadEdge(BasicBlock *BB,
     // If there are no uses outside the block, we're done with this instruction.
     if (UsesToRename.empty())
       continue;
+    SSAUpdate.AddVariable(VarNum, I.getName(), I.getType());
 
-    DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n");
-
-    // We found a use of I outside of BB.  Rename all uses of I that are outside
-    // its block to be uses of the appropriate PHI node etc.  See ValuesInBlocks
-    // with the two values we know.
-    SSAUpdate.Initialize(I.getType(), I.getName());
-    SSAUpdate.AddAvailableValue(BB, &I);
-    SSAUpdate.AddAvailableValue(NewBB, ValueMapping[&I]);
-
-    while (!UsesToRename.empty())
-      SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
-    DEBUG(dbgs() << "\n");
+    // We found a use of I outside of BB - we need to rename all uses of I that
+    // are outside its block to be uses of the appropriate PHI node etc.
+    SSAUpdate.AddAvailableValue(VarNum, BB, &I);
+    SSAUpdate.AddAvailableValue(VarNum, NewBB, ValueMapping[&I]);
+    for (auto U : UsesToRename)
+      SSAUpdate.AddUse(VarNum, U);
+    VarNum++;
   }
 
   // Ok, NewBB is good to go.  Update the terminator of PredBB to jump to
@@ -2037,6 +2040,10 @@ bool JumpThreadingPass::ThreadEdge(BasicBlock *BB,
                      {DominatorTree::Insert, PredBB, NewBB},
                      {DominatorTree::Delete, PredBB, BB}});
 
+  // Apply all updates we queued with DDT and get the updated Dominator Tree.
+  DominatorTree *DT = &DDT->flush();
+  SSAUpdate.RewriteAllUses(DT);
+
   // At this point, the IR is fully up to date and consistent.  Do a quick scan
   // over the new instructions and zap any that are constants or dead.  This
   // frequently happens because of phi translation.
diff --git a/llvm/test/Transforms/JumpThreading/removed-use.ll b/llvm/test/Transforms/JumpThreading/removed-use.ll
new file mode 100644
index 0000000..d2c6836
--- /dev/null
+++ b/llvm/test/Transforms/JumpThreading/removed-use.ll
@@ -0,0 +1,28 @@
+; RUN: opt -S < %s -jump-threading | FileCheck %s
+; CHECK-LABEL: @foo
+; CHECK: bb6:
+; CHECK-NEXT: ret void
+; CHECK: bb3:
+; CHECK: br label %bb3
+define void @foo() {
+entry:
+  br i1 true, label %bb6, label %bb3
+
+bb3:
+  %x0 = phi i32 [ undef, %entry ], [ %x1, %bb5 ]
+  %y  = and i64 undef, 1
+  %p  = icmp ne i64 %y, 0
+  br i1 %p, label %bb4, label %bb5
+
+bb4:
+  br label %bb5
+
+bb5:
+  %x1 = phi i32 [ %x0, %bb3 ], [ %x0, %bb4 ]
+  %z  = phi i32 [ 0, %bb3 ], [ 1, %bb4 ]
+  %q  = icmp eq i32 %z, 0
+  br i1 %q, label %bb3, label %bb6
+
+bb6:
+  ret void
+}
-- 
2.7.4