diff --git a/lib/Transforms/InstCombine/InstCombine.h b/lib/Transforms/InstCombine/InstCombine.h
index da7a22c0c6e..6c0d4e74a7a 100644
--- a/lib/Transforms/InstCombine/InstCombine.h
+++ b/lib/Transforms/InstCombine/InstCombine.h
@@ -14,7 +14,6 @@
 #include "llvm/Analysis/AssumptionTracker.h"
 #include "llvm/Analysis/TargetFolder.h"
 #include "llvm/Analysis/ValueTracking.h"
-#include "llvm/IR/Dominators.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InstVisitor.h"
 #include "llvm/IR/IntrinsicInst.h"
@@ -99,7 +98,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner
   AssumptionTracker *AT;
   const DataLayout *DL;
   TargetLibraryInfo *TLI;
-  DominatorTree *DT;
+  DominatorTree *DT; // not required
   bool MadeIRChange;
   LibCallSimplifier *Simplifier;
   bool MinimizeSize;
@@ -114,8 +113,7 @@ public:
   BuilderTy *Builder;
 
   static char ID; // Pass identification, replacement for typeid
-  InstCombiner()
-      : FunctionPass(ID), DL(nullptr), DT(nullptr), Builder(nullptr) {
+  InstCombiner() : FunctionPass(ID), DL(nullptr), Builder(nullptr) {
     MinimizeSize = false;
     initializeInstCombinerPass(*PassRegistry::getPassRegistry());
   }
@@ -244,11 +242,6 @@ public:
 
   // visitInstruction - Specify what to return for unhandled instructions...
   Instruction *visitInstruction(Instruction &I) { return nullptr; }
-  bool dominatesAllUses(const Instruction *DI, const Instruction *UI,
-                        const BasicBlock *DB) const;
-  bool replacedSelectWithOperand(SelectInst *SI, const ICmpInst *Icmp,
-                                 const ConstantInt *CI1,
-                                 const ConstantInt *CI2);
 
 private:
   bool ShouldChangeType(Type *From, Type *To) const;
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index f6d605ee8e3..00623b1cbf6 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2429,125 +2429,6 @@ static bool swapMayExposeCSEOpportunities(const Value * Op0,
   return GlobalSwapBenefits > 0;
 }
 
-/// \brief Check that one use is in the same block as the definition and all
-/// other uses are in blocks dominated by a given block
-///
-/// \param DI Definition
-/// \param UI Use
-/// \param DB Block that must dominate all uses of \p DI outside
-///           the parent block
-/// \return true when \p UI is the only use of \p DI in the parent block
-/// and all other uses of \p DI are in blocks dominated by \p DB.
-///
-bool InstCombiner::dominatesAllUses(const Instruction *DI,
-                                    const Instruction *UI,
-                                    const BasicBlock *DB) const {
-  assert(DI && UI && "Instruction not defined\n");
-  if (DI->getParent() != UI->getParent())
-    return false;
-  // DominatorTree available?
-  if (!DT)
-    return false;
-  for (const User *U : DI->users()) {
-    auto *Usr = cast<Instruction>(U);
-    if (Usr != UI && !DT->dominates(DB, Usr->getParent()))
-      return false;
-  }
-  return true;
-}
-
-///
-/// true when the instruction sequence within a block is select-cmp-br.
-///
-static bool isChainSelectCmpBranch(const SelectInst *SI) {
-  const BasicBlock *BB = SI->getParent();
-  if (!BB)
-    return false;
-  auto *BI = dyn_cast_or_null<BranchInst>(BB->getTerminator());
-  if (!BI || BI->getNumSuccessors() != 2)
-    return false;
-  auto *IC = dyn_cast<ICmpInst>(BI->getCondition());
-  if (!IC || (IC->getOperand(0) != SI && IC->getOperand(1) != SI))
-    return false;
-  return true;
-}
-
-///
-/// \brief True when a select result is replaced by one of its operands
-/// in select-icmp sequence. This will eventually result in the elimination
-/// of the select.
-///
-/// \param SI   Select instruction
-/// \param Icmp Compare instruction
-/// \param CI1  'true' when first select operand is equal to RHSC of Icmp
-/// \param CI2  'true' when second select operand is equal to RHSC of Icmp
-///
-/// Notes:
-/// - The replacement is global and requires dominator information
-/// - The caller is responsible for the actual replacement
-///
-/// Example:
-///
-/// entry:
-///  %4 = select i1 %3, %C* %0, %C* null
-///  %5 = icmp eq %C* %4, null
-///  br i1 %5, label %9, label %7
-///  ...
-///  ; <label>:7                                       ; preds = %entry
-///  %8 = getelementptr inbounds %C* %4, i64 0, i32 0
-///  ...
-///
-/// can be transformed to
-///
-///  %5 = icmp eq %C* %0, null
-///  %6 = select i1 %3, i1 %5, i1 true
-///  br i1 %6, label %9, label %7
-///  ...
-///  ; <label>:7                                       ; preds = %entry
-///  %8 = getelementptr inbounds %C* %0, i64 0, i32 0  // replace by %0!
-///
-/// Similar when the first operand of the select is a constant or/and
-/// the compare is for not equal rather than equal.
-///
-/// FIXME: Currently the function considers equal compares only. It should be
-/// possbile to extend it to not equal compares also.
-///
-bool InstCombiner::replacedSelectWithOperand(SelectInst *SI,
-                                             const ICmpInst *Icmp,
-                                             const ConstantInt *CI1,
-                                             const ConstantInt *CI2) {
-  if (isChainSelectCmpBranch(SI) &&
-      Icmp->getPredicate() == ICmpInst::ICMP_EQ) {
-    // Code sequence is select - icmp.eq - br
-    unsigned ReplaceWithOpd = 0;
-    if (CI1 && !CI1->isZero())
-      // The first constant operand of the select and the RHS of
-      // the compare match, so try to substitute
-      // the select results with its second operand
-      // Example:
-      // %4 = select i1 %3, %C* null, %C* %0
-      // %5 = icmp eq %C* %4, null
-      // ==> could replace select with second operand
-      ReplaceWithOpd = 2;
-    else if (CI2 && !CI2->isZero())
-      // Similar when the second operand of the select is a constant
-      // Example:
-      // %4 = select i1 %3, %C* %0, %C* null
-      // %5 = icmp eq %C* %4, null
-      // ==> could replace select with first operand
-      ReplaceWithOpd = 1;
-    if (ReplaceWithOpd) {
-      // Replace select with operand on else path for EQ compares.
-      BasicBlock *Succ = SI->getParent()->getTerminator()->getSuccessor(1);
-      if (InstCombiner::dominatesAllUses(SI, Icmp, Succ)) {
-        SI->replaceAllUsesWith(SI->getOperand(ReplaceWithOpd));
-        return true;
-      }
-    }
-  }
-  return false;
-}
-
 Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
   bool Changed = false;
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@@ -3004,21 +2885,8 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
         // fold to a constant (in which case the icmp is replaced with a select
         // which will usually simplify) or this is the only user of the
         // select (in which case we are trading a select+icmp for a simpler
-        // select+icmp) or all uses of the select can be replaced based on
-        // dominance information ("Global cases").
-        bool Transform = false;
-        if (Op1 && Op2)
-          Transform = true;
-        else if (Op1 || Op2) {
-          if (LHSI->hasOneUse())
-            Transform = true;
-          else
-            // Global cases
-            Transform = replacedSelectWithOperand(
-                cast<SelectInst>(LHSI), &I, dyn_cast_or_null<ConstantInt>(Op1),
-                dyn_cast_or_null<ConstantInt>(Op2));
-        }
-        if (Transform) {
+        // select+icmp).
+        if ((Op1 && Op2) || (LHSI->hasOneUse() && (Op1 || Op2))) {
           if (!Op1)
             Op1 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(1),
                                       RHSC, I.getName());
diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index a3a29b4e0bd..ac0c01e3c7b 100644
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -90,7 +90,6 @@ INITIALIZE_PASS_BEGIN(InstCombiner, "instcombine",
                 "Combine redundant instructions", false, false)
 INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_END(InstCombiner, "instcombine",
                 "Combine redundant instructions", false, false)
 
@@ -98,8 +97,6 @@ void InstCombiner::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesCFG();
   AU.addRequired<AssumptionTracker>();
   AU.addRequired<TargetLibraryInfo>();
-  AU.addRequired<DominatorTreeWrapperPass>();
-  AU.addPreserved<DominatorTreeWrapperPass>();
 }
 
 
@@ -2936,9 +2933,12 @@ bool InstCombiner::runOnFunction(Function &F) {
   AT = &getAnalysis<AssumptionTracker>();
   DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
   DL = DLP ? &DLP->getDataLayout() : nullptr;
-  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
   TLI = &getAnalysis<TargetLibraryInfo>();
 
+  DominatorTreeWrapperPass *DTWP =
+      getAnalysisIfAvailable<DominatorTreeWrapperPass>();
+  DT = DTWP ? &DTWP->getDomTree() : nullptr;
+
   // Minimizing size?
   MinimizeSize = F.getAttributes().hasAttribute(AttributeSet::FunctionIndex,
                                                 Attribute::MinSize);
diff --git a/test/Transforms/InstCombine/pr12338.ll b/test/Transforms/InstCombine/pr12338.ll
index 051c21ca41a..d34600f0fa5 100644
--- a/test/Transforms/InstCombine/pr12338.ll
+++ b/test/Transforms/InstCombine/pr12338.ll
@@ -2,11 +2,11 @@
 
 define void @entry() nounwind {
 entry:
-; CHECK: br label %for.cond
   br label %for.cond
 
 for.cond:
   %local = phi <1 x i32> [ <i32 0>, %entry ], [ %phi2, %cond.end47 ]
+; CHECK: sub <1 x i32> <i32 92>, %local
   %phi3 = sub <1 x i32> zeroinitializer, %local
   br label %cond.end
 
diff --git a/test/Transforms/InstCombine/pr21199.ll b/test/Transforms/InstCombine/pr21199.ll
deleted file mode 100644
index e6599fb640d..00000000000
--- a/test/Transforms/InstCombine/pr21199.ll
+++ /dev/null
@@ -1,25 +0,0 @@
-; do not replace a 'select' with 'or' in 'select - cmp - br' sequence
-; RUN: opt -instcombine -S < %s | FileCheck %s
-target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
-target triple = "x86_64-unknown-linux-gnu"
-
-declare void @f(i32)
-
-define void @test(i32 %len) {
-entry:
-  %cmp = icmp ult i32 %len, 8
-  %cond = select i1 %cmp, i32 %len, i32 8
-  %cmp11 = icmp ult i32 0, %cond
-  br i1 %cmp11, label %for.body, label %for.end
-
-for.body:                                         ; preds = %entry, %for.body
-  %i.02 = phi i32 [ %inc, %for.body ], [ 0, %entry ]
-  tail call void @f(i32 %cond)
-  %inc = add i32 %i.02, 1
-  %cmp1 = icmp ult i32 %inc, %cond
-  br i1 %cmp1, label %for.body, label %for.end
-
-for.end:                                          ; preds = %for.body, %entry
-  ret void
-; CHECK: select
-}
diff --git a/test/Transforms/InstCombine/select-cmp-br.ll b/test/Transforms/InstCombine/select-cmp-br.ll
deleted file mode 100644
index 2e999510b42..00000000000
--- a/test/Transforms/InstCombine/select-cmp-br.ll
+++ /dev/null
@@ -1,127 +0,0 @@
-; Replace a 'select' with 'or' in 'select - cmp [eq|ne] - br' sequence
-; RUN: opt -instcombine -S < %s | FileCheck %s
-
-%C = type <{ %struct.S }>
-%struct.S = type { i64*, i32, i32 }
-
-declare void @bar(%struct.S *) #1
-
-define void @test1(%C*) {
-entry:
-  %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
-  %m = load i64** %1, align 8
-  %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
-  %n = load i64** %2, align 8
-  %3 = getelementptr inbounds i64* %m, i64 9
-  %4 = bitcast i64* %3 to i64 (%C*)**
-  %5 = load i64 (%C*)** %4, align 8
-  %6 = icmp eq i64* %m, %n
-  %7 = select i1 %6, %C* %0, %C* null
-  %8 = icmp eq %C* %7, null
-  br i1 %8, label %12, label %10
-
-; <label>:9                                       ; preds = %10, %12
-  ret void
-
-; <label>:10                                      ; preds = %entry
-  %11 = getelementptr inbounds %C* %7, i64 0, i32 0
-  tail call void @bar(%struct.S* %11)
-  br label %9
-
-; <label>:12                                      ; preds = %entry
-  %13 = tail call i64 %5(%C* %0)
-  br label %9
-; CHECK-LABEL: @test1(
-; CHECK-NOT: select
-; CHECK: or
-}
-
-define void @test2(%C*) {
-entry:
-  %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
-  %m = load i64** %1, align 8
-  %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
-  %n = load i64** %2, align 8
-  %3 = getelementptr inbounds i64* %m, i64 9
-  %4 = bitcast i64* %3 to i64 (%C*)**
-  %5 = load i64 (%C*)** %4, align 8
-  %6 = icmp eq i64* %m, %n
-  %7 = select i1 %6, %C* null, %C* %0
-  %8 = icmp eq %C* %7, null
-  br i1 %8, label %12, label %10
-
-; <label>:9                                       ; preds = %10, %12
-  ret void
-
-; <label>:10                                      ; preds = %entry
-  %11 = getelementptr inbounds %C* %7, i64 0, i32 0
-  tail call void @bar(%struct.S* %11)
-  br label %9
-
-; <label>:12                                      ; preds = %entry
-  %13 = tail call i64 %5(%C* %0)
-  br label %9
-; CHECK-LABEL: @test2(
-; CHECK-NOT: select
-; CHECK: or
-}
-
-define void @test3(%C*) {
-entry:
-  %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
-  %m = load i64** %1, align 8
-  %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
-  %n = load i64** %2, align 8
-  %3 = getelementptr inbounds i64* %m, i64 9
-  %4 = bitcast i64* %3 to i64 (%C*)**
-  %5 = load i64 (%C*)** %4, align 8
-  %6 = icmp eq i64* %m, %n
-  %7 = select i1 %6, %C* %0, %C* null
-  %8 = icmp ne %C* %7, null
-  br i1 %8, label %10, label %12
-
-; <label>:9                                       ; preds = %10, %12
-  ret void
-
-; <label>:10                                      ; preds = %entry
-  %11 = getelementptr inbounds %C* %7, i64 0, i32 0
-  tail call void @bar(%struct.S* %11)
-  br label %9
-
-; <label>:12                                      ; preds = %entry
-  %13 = tail call i64 %5(%C* %0)
-  br label %9
-; CHECK-LABEL: @test3(
-; CHECK-NOT: select
-; CHECK: or
-}
-
-define void @test4(%C*) {
-entry:
-  %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
-  %m = load i64** %1, align 8
-  %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
-  %n = load i64** %2, align 8
-  %3 = getelementptr inbounds i64* %m, i64 9
-  %4 = bitcast i64* %3 to i64 (%C*)**
-  %5 = load i64 (%C*)** %4, align 8
-  %6 = icmp eq i64* %m, %n
-  %7 = select i1 %6, %C* null, %C* %0
-  %8 = icmp ne %C* %7, null
-  br i1 %8, label %10, label %12
-
-; <label>:9                                       ; preds = %10, %12
-  ret void
-
-; <label>:10                                      ; preds = %entry
-  %11 = getelementptr inbounds %C* %7, i64 0, i32 0
-  tail call void @bar(%struct.S* %11)
-  br label %9
-
-; <label>:12                                      ; preds = %entry
-  %13 = tail call i64 %5(%C* %0)
-  br label %9
-; CHECK-LABEL: @test4(
-; CHECK-NOT: select
-; CHECK: or
-}