From 849db7fa025496cf1bf9cb8a4ac67f875d439039 Mon Sep 17 00:00:00 2001
From: Xin Tong <trent.xin.tong@gmail.com>
Date: Mon, 18 Jun 2018 23:20:08 +0000
Subject: [PATCH] Revert "Simplify blockaddress usage before giving up in
 MergeBlockIntoPredecessor"

This reverts commit f976cf4cca0794267f28b54e468007fd476d37d9.

I am reverting this because it causes break in a few bots and its going
to take me sometime to look at this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@334993 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/BasicBlockUtils.cpp      |  9 +-----
 .../dce-cond-after-folding-terminator.ll      |  5 +++-
 .../Transforms/Utils/BasicBlockUtils.cpp      | 28 -------------------
 3 files changed, 5 insertions(+), 37 deletions(-)

diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 4b89b0435e0..59837042550 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -119,14 +119,7 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT,
                                      LoopInfo *LI,
                                      MemoryDependenceResults *MemDep) {
   // Don't merge away blocks who have their address taken.
-  if (BB->hasAddressTaken()) {
-    // If the block has its address taken, it may be a tree of dead constants
-    // hanging off of it.  These shouldn't keep the block alive.
-    BlockAddress *BA = BlockAddress::get(BB);
-    BA->removeDeadConstantUsers();
-    if (!BA->use_empty())
-      return false;
-  }
+  if (BB->hasAddressTaken()) return false;
 
   // Can't merge if there are multiple predecessors, or no predecessors.
   BasicBlock *PredBB = BB->getUniquePredecessor();
diff --git a/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll b/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll
index a15cdd6a28f..036a615e7ff 100644
--- a/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll
+++ b/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll
@@ -37,7 +37,10 @@ define void @test_indirectbr(i32 %x) {
 entry:
 ; CHECK-LABEL: @test_indirectbr(
 ; CHECK-NEXT: entry:
-; CHECK-NEXT: ret void
+; Ideally this should now check:
+;   CHK-NEXT: ret void
+; But that doesn't happen yet. Instead:
+; CHECK-NEXT: br label %L1
 
   %label = bitcast i8* blockaddress(@test_indirectbr, %L1) to i8*
   indirectbr i8* %label, [label %L1, label %L2]
diff --git a/unittests/Transforms/Utils/BasicBlockUtils.cpp b/unittests/Transforms/Utils/BasicBlockUtils.cpp
index 590e7f6ada6..2d0a9302011 100644
--- a/unittests/Transforms/Utils/BasicBlockUtils.cpp
+++ b/unittests/Transforms/Utils/BasicBlockUtils.cpp
@@ -50,31 +50,3 @@ TEST(BasicBlockUtils, SplitBlockPredecessors) {
   SplitBlockPredecessors(&F->getEntryBlock(), {}, "split.entry", &DT);
   EXPECT_TRUE(DT.verify());
 }
-
-TEST(BasicBlockUtils, MergeBlockIntoPredecessor) {
-  LLVMContext C;
-  std::unique_ptr<Module> M = parseIR(C,
-                                      R"(
-
-      define i32 @f(i8* %str) {
-      entry:
-        %dead = extractvalue [1 x i8*] [ i8* blockaddress(@f, %L0) ], 0
-        br label %L0
-      L0:
-        ret i32 0
-      }
-      )");
-
-  // First remove the dead instruction to empty the usage of the constant
-  // containing blockaddress(@f, %L0)
-  Function *F = M->getFunction("f");
-  auto BBI = F->begin();
-  Instruction *DI = &*((*BBI).begin());
-  EXPECT_TRUE(DI->use_empty());
-  DI->eraseFromParent();
-
-  // Get L0 and make sure that it can be merged into entry block.
-  ++BBI;
-  BasicBlock *BB = &(*BBI);
-  EXPECT_TRUE(MergeBlockIntoPredecessor(BB));
-}