[InstCombine] re-commit r218721 with fix for pr21199

The icmp-select-icmp optimization targets select-icmp.eq
only. This is now ensured by testing the branch predicate
explictly. This commit also includes the test case for pr21199.

llvm-svn: 219282
diff --git a/llvm/lib/Transforms/InstCombine/InstCombine.h b/llvm/lib/Transforms/InstCombine/InstCombine.h
index 6c0d4e7..da7a22c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombine.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombine.h
@@ -14,6 +14,7 @@
 #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"
@@ -98,7 +99,7 @@
   AssumptionTracker *AT;
   const DataLayout *DL;
   TargetLibraryInfo *TLI;
-  DominatorTree *DT; // not required
+  DominatorTree *DT;
   bool MadeIRChange;
   LibCallSimplifier *Simplifier;
   bool MinimizeSize;
@@ -113,7 +114,8 @@
   BuilderTy *Builder;
 
   static char ID; // Pass identification, replacement for typeid
-  InstCombiner() : FunctionPass(ID), DL(nullptr), Builder(nullptr) {
+  InstCombiner()
+      : FunctionPass(ID), DL(nullptr), DT(nullptr), Builder(nullptr) {
     MinimizeSize = false;
     initializeInstCombinerPass(*PassRegistry::getPassRegistry());
   }
@@ -242,6 +244,11 @@
 
   // 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;