Update clang, llvm, lld, lldb, compiler-rt and libc++ to 4.0.0 release:

MFC r309142 (by emaste):

Add WITH_LLD_AS_LD build knob

If set it installs LLD as /usr/bin/ld.  LLD (as of version 3.9) is not
capable of linking the world and kernel, but can self-host and link many
substantial applications. GNU ld continues to be used for the world and
kernel build, regardless of how this knob is set.

It is on by default for arm64, and off for all other CPU architectures.

Sponsored by:	The FreeBSD Foundation

MFC r310840:

Reapply 310775, now it also builds correctly if lldb is disabled:

Move llvm-objdump from CLANG_EXTRAS to installed by default

We currently install three tools from binutils 2.17.50: as, ld, and
objdump. Work is underway to migrate to a permissively-licensed
tool-chain, with one goal being the retirement of binutils 2.17.50.

LLVM's llvm-objdump is intended to be compatible with GNU objdump
although it is currently missing some options and may have formatting
differences. Enable it by default for testing and further investigation.
It may later be changed to install as /usr/bin/objdump, it becomes a
fully viable replacement.

Reviewed by:	emaste
Differential Revision:	https://reviews.freebsd.org/D8879

MFC r312855 (by emaste):

Rename LLD_AS_LD to LLD_IS_LD, for consistency with CLANG_IS_CC

Reported by:	Dan McGregor <dan.mcgregor usask.ca>

MFC r313559 | glebius | 2017-02-10 18:34:48 +0100 (Fri, 10 Feb 2017) | 5 lines

Don't check struct rtentry on FreeBSD, it is an internal kernel structure.
On other systems it may be API structure for SIOCADDRT/SIOCDELRT.

Reviewed by:	emaste, dim

MFC r314152 (by jkim):

Remove an assembler flag, which is redundant since r309124.  The upstream
took care of it by introducing a macro NO_EXEC_STACK_DIRECTIVE.

http://llvm.org/viewvc/llvm-project?rev=273500&view=rev

Reviewed by:	dim

MFC r314564:

Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
4.0.0 (branches/release_40 296509).  The release will follow soon.

Please note that from 3.5.0 onwards, clang, llvm and lldb require C++11
support to build; see UPDATING for more information.

Also note that as of 4.0.0, lld should be able to link the base system
on amd64 and aarch64.  See the WITH_LLD_IS_LLD setting in src.conf(5).
Though please be aware that this is work in progress.

Release notes for llvm, clang and lld will be available here:
<http://releases.llvm.org/4.0.0/docs/ReleaseNotes.html>
<http://releases.llvm.org/4.0.0/tools/clang/docs/ReleaseNotes.html>
<http://releases.llvm.org/4.0.0/tools/lld/docs/ReleaseNotes.html>

Thanks to Ed Maste, Jan Beich, Antoine Brodin and Eric Fiselier for
their help.

Relnotes:	yes
Exp-run:	antoine
PR:		215969, 216008

MFC r314708:

For now, revert r287232 from upstream llvm trunk (by Daniil Fukalov):

  [SCEV] limit recursion depth of CompareSCEVComplexity

  Summary:
  CompareSCEVComplexity goes too deep (50+ on a quite a big unrolled
  loop) and runs almost infinite time.

  Added cache of "equal" SCEV pairs to earlier cutoff of further
  estimation. Recursion depth limit was also introduced as a parameter.

  Reviewers: sanjoy

  Subscribers: mzolotukhin, tstellarAMD, llvm-commits

  Differential Revision: https://reviews.llvm.org/D26389

This commit is the cause of excessive compile times on skein_block.c
(and possibly other files) during kernel builds on amd64.

We never saw the problematic behavior described in this upstream commit,
so for now it is better to revert it.  An upstream bug has been filed
here: https://bugs.llvm.org/show_bug.cgi?id=32142

Reported by:	mjg

MFC r314795:

Reapply r287232 from upstream llvm trunk (by Daniil Fukalov):

  [SCEV] limit recursion depth of CompareSCEVComplexity

  Summary:
  CompareSCEVComplexity goes too deep (50+ on a quite a big unrolled
  loop) and runs almost infinite time.

  Added cache of "equal" SCEV pairs to earlier cutoff of further
  estimation. Recursion depth limit was also introduced as a parameter.

  Reviewers: sanjoy

  Subscribers: mzolotukhin, tstellarAMD, llvm-commits

  Differential Revision: https://reviews.llvm.org/D26389

Pull in r296992 from upstream llvm trunk (by Sanjoy Das):

  [SCEV] Decrease the recursion threshold for CompareValueComplexity

  Fixes PR32142.

  r287232 accidentally increased the recursion threshold for
  CompareValueComplexity from 2 to 32.  This change reverses that
  change by introducing a separate flag for CompareValueComplexity's
  threshold.

The latter revision fixes the excessive compile times for skein_block.c.

MFC r314907 | mmel | 2017-03-08 12:40:27 +0100 (Wed, 08 Mar 2017) | 7 lines

Unbreak ARMv6 world.

The new compiler_rt library imported with clang 4.0.0 have several fatal
issues (non-functional __udivsi3 for example) with ARM specific instrict
functions. As temporary workaround, until upstream solve these problems,
disable all thumb[1][2] related feature.

MFC r315016:

Update clang, llvm, lld, lldb, compiler-rt and libc++ to 4.0.0 release.
We were already very close to the last release candidate, so this is a
pretty minor update.

Relnotes:	yes

MFC r316005:

Revert r314907, and pull in r298713 from upstream compiler-rt trunk (by
Weiming Zhao):

  builtins: Select correct code fragments when compiling for Thumb1/Thum2/ARM ISA.

  Summary:
  Value of __ARM_ARCH_ISA_THUMB isn't based on the actual compilation
  mode (-mthumb, -marm), it reflect's capability of given CPU.

  Due to this:
   - use  __tbumb__ and __thumb2__ insteand of __ARM_ARCH_ISA_THUMB
   - use '.thumb' directive consistently  in all affected files
   - decorate all thumb functions using
     DEFINE_COMPILERRT_THUMB_FUNCTION()

  ---------
  Note: This patch doesn't fix broken Thumb1 variant of __udivsi3 !

  Reviewers: weimingz, rengolin, compnerd

  Subscribers: aemerson, dim

  Differential Revision: https://reviews.llvm.org/D30938

Discussed with:	mmel

1 files changed, 296 insertions, 85 deletions

diff --git a/contrib/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/contrib/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 2055615..e74b590 100644
--- a/contrib/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/contrib/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "InstCombineInternal.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/PatternMatch.h"
@@ -161,8 +162,8 @@ Value *InstCombiner::EvaluateInDifferentType(Value *V, Type *Ty,
   if (Constant *C = dyn_cast<Constant>(V)) {
     C = ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/);
     // If we got a constantexpr back, try to simplify it with DL info.
-    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
-      C = ConstantFoldConstantExpression(CE, DL, TLI);
+    if (Constant *FoldedC = ConstantFoldConstant(C, DL, &TLI))
+      C = FoldedC;
     return C;
   }
 
@@ -227,20 +228,14 @@ Value *InstCombiner::EvaluateInDifferentType(Value *V, Type *Ty,
   return InsertNewInstWith(Res, *I);
 }
 
+Instruction::CastOps InstCombiner::isEliminableCastPair(const CastInst *CI1,
+                                                        const CastInst *CI2) {
+  Type *SrcTy = CI1->getSrcTy();
+  Type *MidTy = CI1->getDestTy();
+  Type *DstTy = CI2->getDestTy();
 
-/// This function is a wrapper around CastInst::isEliminableCastPair. It
-/// simply extracts arguments and returns what that function returns.
-static Instruction::CastOps
-isEliminableCastPair(const CastInst *CI, ///< First cast instruction
-                     unsigned opcode,    ///< Opcode for the second cast
-                     Type *DstTy,        ///< Target type for the second cast
-                     const DataLayout &DL) {
-  Type *SrcTy = CI->getOperand(0)->getType();   // A from above
-  Type *MidTy = CI->getType();                  // B from above
-
-  // Get the opcodes of the two Cast instructions
-  Instruction::CastOps firstOp = Instruction::CastOps(CI->getOpcode());
-  Instruction::CastOps secondOp = Instruction::CastOps(opcode);
+  Instruction::CastOps firstOp = Instruction::CastOps(CI1->getOpcode());
+  Instruction::CastOps secondOp = Instruction::CastOps(CI2->getOpcode());
   Type *SrcIntPtrTy =
       SrcTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(SrcTy) : nullptr;
   Type *MidIntPtrTy =
@@ -260,54 +255,28 @@ isEliminableCastPair(const CastInst *CI, ///< First cast instruction
   return Instruction::CastOps(Res);
 }
 
-/// Return true if the cast from "V to Ty" actually results in any code being
-/// generated and is interesting to optimize out.
-/// If the cast can be eliminated by some other simple transformation, we prefer
-/// to do the simplification first.
-bool InstCombiner::ShouldOptimizeCast(Instruction::CastOps opc, const Value *V,
-                                      Type *Ty) {
-  // Noop casts and casts of constants should be eliminated trivially.
-  if (V->getType() == Ty || isa<Constant>(V)) return false;
-
-  // If this is another cast that can be eliminated, we prefer to have it
-  // eliminated.
-  if (const CastInst *CI = dyn_cast<CastInst>(V))
-    if (isEliminableCastPair(CI, opc, Ty, DL))
-      return false;
-
-  // If this is a vector sext from a compare, then we don't want to break the
-  // idiom where each element of the extended vector is either zero or all ones.
-  if (opc == Instruction::SExt && isa<CmpInst>(V) && Ty->isVectorTy())
-    return false;
-
-  return true;
-}
-
-
 /// @brief Implement the transforms common to all CastInst visitors.
 Instruction *InstCombiner::commonCastTransforms(CastInst &CI) {
   Value *Src = CI.getOperand(0);
 
-  // Many cases of "cast of a cast" are eliminable. If it's eliminable we just
-  // eliminate it now.
-  if (CastInst *CSrc = dyn_cast<CastInst>(Src)) {   // A->B->C cast
-    if (Instruction::CastOps opc =
-            isEliminableCastPair(CSrc, CI.getOpcode(), CI.getType(), DL)) {
+  // Try to eliminate a cast of a cast.
+  if (auto *CSrc = dyn_cast<CastInst>(Src)) {   // A->B->C cast
+    if (Instruction::CastOps NewOpc = isEliminableCastPair(CSrc, &CI)) {
       // The first cast (CSrc) is eliminable so we need to fix up or replace
       // the second cast (CI). CSrc will then have a good chance of being dead.
-      return CastInst::Create(opc, CSrc->getOperand(0), CI.getType());
+      return CastInst::Create(NewOpc, CSrc->getOperand(0), CI.getType());
     }
   }
 
-  // If we are casting a select then fold the cast into the select
-  if (SelectInst *SI = dyn_cast<SelectInst>(Src))
+  // If we are casting a select, then fold the cast into the select.
+  if (auto *SI = dyn_cast<SelectInst>(Src))
     if (Instruction *NV = FoldOpIntoSelect(CI, SI))
       return NV;
 
-  // If we are casting a PHI then fold the cast into the PHI
+  // If we are casting a PHI, then fold the cast into the PHI.
   if (isa<PHINode>(Src)) {
-    // We don't do this if this would create a PHI node with an illegal type if
-    // it is currently legal.
+    // Don't do this if it would create a PHI node with an illegal type from a
+    // legal type.
     if (!Src->getType()->isIntegerTy() || !CI.getType()->isIntegerTy() ||
         ShouldChangeType(CI.getType(), Src->getType()))
       if (Instruction *NV = FoldOpIntoPhi(CI))
@@ -474,19 +443,39 @@ static Instruction *foldVecTruncToExtElt(TruncInst &Trunc, InstCombiner &IC,
   return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(Elt));
 }
 
+/// Try to narrow the width of bitwise logic instructions with constants.
+Instruction *InstCombiner::shrinkBitwiseLogic(TruncInst &Trunc) {
+  Type *SrcTy = Trunc.getSrcTy();
+  Type *DestTy = Trunc.getType();
+  if (isa<IntegerType>(SrcTy) && !ShouldChangeType(SrcTy, DestTy))
+    return nullptr;
+
+  BinaryOperator *LogicOp;
+  Constant *C;
+  if (!match(Trunc.getOperand(0), m_OneUse(m_BinOp(LogicOp))) ||
+      !LogicOp->isBitwiseLogicOp() ||
+      !match(LogicOp->getOperand(1), m_Constant(C)))
+    return nullptr;
+
+  // trunc (logic X, C) --> logic (trunc X, C')
+  Constant *NarrowC = ConstantExpr::getTrunc(C, DestTy);
+  Value *NarrowOp0 = Builder->CreateTrunc(LogicOp->getOperand(0), DestTy);
+  return BinaryOperator::Create(LogicOp->getOpcode(), NarrowOp0, NarrowC);
+}
+
 Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
   if (Instruction *Result = commonCastTransforms(CI))
     return Result;
 
   // Test if the trunc is the user of a select which is part of a
   // minimum or maximum operation. If so, don't do any more simplification.
-  // Even simplifying demanded bits can break the canonical form of a 
+  // Even simplifying demanded bits can break the canonical form of a
   // min/max.
   Value *LHS, *RHS;
   if (SelectInst *SI = dyn_cast<SelectInst>(CI.getOperand(0)))
     if (matchSelectPattern(SI, LHS, RHS).Flavor != SPF_UNKNOWN)
       return nullptr;
-  
+
   // See if we can simplify any instructions used by the input whose sole
   // purpose is to compute bits we don't care about.
   if (SimplifyDemandedInstructionBits(CI))
@@ -562,14 +551,26 @@ Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
     }
   }
 
-  // Transform "trunc (and X, cst)" -> "and (trunc X), cst" so long as the dest
-  // type isn't non-native.
+  if (Instruction *I = shrinkBitwiseLogic(CI))
+    return I;
+
   if (Src->hasOneUse() && isa<IntegerType>(SrcTy) &&
-      ShouldChangeType(SrcTy, DestTy) &&
-      match(Src, m_And(m_Value(A), m_ConstantInt(Cst)))) {
-    Value *NewTrunc = Builder->CreateTrunc(A, DestTy, A->getName() + ".tr");
-    return BinaryOperator::CreateAnd(NewTrunc,
-                                     ConstantExpr::getTrunc(Cst, DestTy));
+      ShouldChangeType(SrcTy, DestTy)) {
+    // Transform "trunc (shl X, cst)" -> "shl (trunc X), cst" so long as the
+    // dest type is native and cst < dest size.
+    if (match(Src, m_Shl(m_Value(A), m_ConstantInt(Cst))) &&
+        !match(A, m_Shr(m_Value(), m_Constant()))) {
+      // Skip shifts of shift by constants. It undoes a combine in
+      // FoldShiftByConstant and is the extend in reg pattern.
+      const unsigned DestSize = DestTy->getScalarSizeInBits();
+      if (Cst->getValue().ult(DestSize)) {
+        Value *NewTrunc = Builder->CreateTrunc(A, DestTy, A->getName() + ".tr");
+
+        return BinaryOperator::Create(
+          Instruction::Shl, NewTrunc,
+          ConstantInt::get(DestTy, Cst->getValue().trunc(DestSize)));
+      }
+    }
   }
 
   if (Instruction *I = foldVecTruncToExtElt(CI, *this, DL))
@@ -578,10 +579,8 @@ Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
   return nullptr;
 }
 
-/// Transform (zext icmp) to bitwise / integer operations in order to eliminate
-/// the icmp.
-Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
-                                             bool DoXform) {
+Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, ZExtInst &CI,
+                                             bool DoTransform) {
   // If we are just checking for a icmp eq of a single bit and zext'ing it
   // to an integer, then shift the bit to the appropriate place and then
   // cast to integer to avoid the comparison.
@@ -592,7 +591,7 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
     // zext (x >s -1) to i32 --> (x>>u31)^1  true if signbit clear.
     if ((ICI->getPredicate() == ICmpInst::ICMP_SLT && Op1CV == 0) ||
         (ICI->getPredicate() == ICmpInst::ICMP_SGT && Op1CV.isAllOnesValue())) {
-      if (!DoXform) return ICI;
+      if (!DoTransform) return ICI;
 
       Value *In = ICI->getOperand(0);
       Value *Sh = ConstantInt::get(In->getType(),
@@ -627,7 +626,7 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
 
       APInt KnownZeroMask(~KnownZero);
       if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
-        if (!DoXform) return ICI;
+        if (!DoTransform) return ICI;
 
         bool isNE = ICI->getPredicate() == ICmpInst::ICMP_NE;
         if (Op1CV != 0 && (Op1CV != KnownZeroMask)) {
@@ -655,7 +654,9 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
 
         if (CI.getType() == In->getType())
           return replaceInstUsesWith(CI, In);
-        return CastInst::CreateIntegerCast(In, CI.getType(), false/*ZExt*/);
+
+        Value *IntCast = Builder->CreateIntCast(In, CI.getType(), false);
+        return replaceInstUsesWith(CI, IntCast);
       }
     }
   }
@@ -678,7 +679,7 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
         APInt KnownBits = KnownZeroLHS | KnownOneLHS;
         APInt UnknownBit = ~KnownBits;
         if (UnknownBit.countPopulation() == 1) {
-          if (!DoXform) return ICI;
+          if (!DoTransform) return ICI;
 
           Value *Result = Builder->CreateXor(LHS, RHS);
 
@@ -760,9 +761,7 @@ static bool canEvaluateZExtd(Value *V, Type *Ty, unsigned &BitsToClear,
 
     // If the operation is an AND/OR/XOR and the bits to clear are zero in the
     // other side, BitsToClear is ok.
-    if (Tmp == 0 &&
-        (Opc == Instruction::And || Opc == Instruction::Or ||
-         Opc == Instruction::Xor)) {
+    if (Tmp == 0 && I->isBitwiseLogicOp()) {
       // We use MaskedValueIsZero here for generality, but the case we care
       // about the most is constant RHS.
       unsigned VSize = V->getType()->getScalarSizeInBits();
@@ -922,16 +921,26 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
 
   BinaryOperator *SrcI = dyn_cast<BinaryOperator>(Src);
   if (SrcI && SrcI->getOpcode() == Instruction::Or) {
-    // zext (or icmp, icmp) --> or (zext icmp), (zext icmp) if at least one
-    // of the (zext icmp) will be transformed.
+    // zext (or icmp, icmp) -> or (zext icmp), (zext icmp) if at least one
+    // of the (zext icmp) can be eliminated. If so, immediately perform the
+    // according elimination.
     ICmpInst *LHS = dyn_cast<ICmpInst>(SrcI->getOperand(0));
     ICmpInst *RHS = dyn_cast<ICmpInst>(SrcI->getOperand(1));
     if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() &&
         (transformZExtICmp(LHS, CI, false) ||
          transformZExtICmp(RHS, CI, false))) {
+      // zext (or icmp, icmp) -> or (zext icmp), (zext icmp)
       Value *LCast = Builder->CreateZExt(LHS, CI.getType(), LHS->getName());
       Value *RCast = Builder->CreateZExt(RHS, CI.getType(), RHS->getName());
-      return BinaryOperator::Create(Instruction::Or, LCast, RCast);
+      BinaryOperator *Or = BinaryOperator::Create(Instruction::Or, LCast, RCast);
+
+      // Perform the elimination.
+      if (auto *LZExt = dyn_cast<ZExtInst>(LCast))
+        transformZExtICmp(LHS, *LZExt);
+      if (auto *RZExt = dyn_cast<ZExtInst>(RCast))
+        transformZExtICmp(RHS, *RZExt);
+
+      return Or;
     }
   }
 
@@ -952,14 +961,6 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
     return BinaryOperator::CreateXor(Builder->CreateAnd(X, ZC), ZC);
   }
 
-  // zext (xor i1 X, true) to i32  --> xor (zext i1 X to i32), 1
-  if (SrcI && SrcI->hasOneUse() &&
-      SrcI->getType()->getScalarType()->isIntegerTy(1) &&
-      match(SrcI, m_Not(m_Value(X))) && (!X->hasOneUse() || !isa<CmpInst>(X))) {
-    Value *New = Builder->CreateZExt(X, CI.getType());
-    return BinaryOperator::CreateXor(New, ConstantInt::get(CI.getType(), 1));
-  }
-
   return nullptr;
 }
 
@@ -1132,7 +1133,7 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
   Type *SrcTy = Src->getType(), *DestTy = CI.getType();
 
   // If we know that the value being extended is positive, we can use a zext
-  // instead. 
+  // instead.
   bool KnownZero, KnownOne;
   ComputeSignBit(Src, KnownZero, KnownOne, 0, &CI);
   if (KnownZero) {
@@ -1238,14 +1239,14 @@ static Value *lookThroughFPExtensions(Value *V) {
     if (CFP->getType() == Type::getPPC_FP128Ty(V->getContext()))
       return V;  // No constant folding of this.
     // See if the value can be truncated to half and then reextended.
-    if (Value *V = fitsInFPType(CFP, APFloat::IEEEhalf))
+    if (Value *V = fitsInFPType(CFP, APFloat::IEEEhalf()))
       return V;
     // See if the value can be truncated to float and then reextended.
-    if (Value *V = fitsInFPType(CFP, APFloat::IEEEsingle))
+    if (Value *V = fitsInFPType(CFP, APFloat::IEEEsingle()))
       return V;
     if (CFP->getType()->isDoubleTy())
       return V;  // Won't shrink.
-    if (Value *V = fitsInFPType(CFP, APFloat::IEEEdouble))
+    if (Value *V = fitsInFPType(CFP, APFloat::IEEEdouble()))
       return V;
     // Don't try to shrink to various long double types.
   }
@@ -1789,6 +1790,205 @@ static Instruction *canonicalizeBitCastExtElt(BitCastInst &BitCast,
   return ExtractElementInst::Create(NewBC, ExtElt->getIndexOperand());
 }
 
+/// Change the type of a bitwise logic operation if we can eliminate a bitcast.
+static Instruction *foldBitCastBitwiseLogic(BitCastInst &BitCast,
+                                            InstCombiner::BuilderTy &Builder) {
+  Type *DestTy = BitCast.getType();
+  BinaryOperator *BO;
+  if (!DestTy->getScalarType()->isIntegerTy() ||
+      !match(BitCast.getOperand(0), m_OneUse(m_BinOp(BO))) ||
+      !BO->isBitwiseLogicOp())
+    return nullptr;
+  
+  // FIXME: This transform is restricted to vector types to avoid backend
+  // problems caused by creating potentially illegal operations. If a fix-up is
+  // added to handle that situation, we can remove this check.
+  if (!DestTy->isVectorTy() || !BO->getType()->isVectorTy())
+    return nullptr;
+  
+  Value *X;
+  if (match(BO->getOperand(0), m_OneUse(m_BitCast(m_Value(X)))) &&
+      X->getType() == DestTy && !isa<Constant>(X)) {
+    // bitcast(logic(bitcast(X), Y)) --> logic'(X, bitcast(Y))
+    Value *CastedOp1 = Builder.CreateBitCast(BO->getOperand(1), DestTy);
+    return BinaryOperator::Create(BO->getOpcode(), X, CastedOp1);
+  }
+
+  if (match(BO->getOperand(1), m_OneUse(m_BitCast(m_Value(X)))) &&
+      X->getType() == DestTy && !isa<Constant>(X)) {
+    // bitcast(logic(Y, bitcast(X))) --> logic'(bitcast(Y), X)
+    Value *CastedOp0 = Builder.CreateBitCast(BO->getOperand(0), DestTy);
+    return BinaryOperator::Create(BO->getOpcode(), CastedOp0, X);
+  }
+
+  return nullptr;
+}
+
+/// Change the type of a select if we can eliminate a bitcast.
+static Instruction *foldBitCastSelect(BitCastInst &BitCast,
+                                      InstCombiner::BuilderTy &Builder) {
+  Value *Cond, *TVal, *FVal;
+  if (!match(BitCast.getOperand(0),
+             m_OneUse(m_Select(m_Value(Cond), m_Value(TVal), m_Value(FVal)))))
+    return nullptr;
+
+  // A vector select must maintain the same number of elements in its operands.
+  Type *CondTy = Cond->getType();
+  Type *DestTy = BitCast.getType();
+  if (CondTy->isVectorTy()) {
+    if (!DestTy->isVectorTy())
+      return nullptr;
+    if (DestTy->getVectorNumElements() != CondTy->getVectorNumElements())
+      return nullptr;
+  }
+
+  // FIXME: This transform is restricted from changing the select between
+  // scalars and vectors to avoid backend problems caused by creating
+  // potentially illegal operations. If a fix-up is added to handle that
+  // situation, we can remove this check.
+  if (DestTy->isVectorTy() != TVal->getType()->isVectorTy())
+    return nullptr;
+
+  auto *Sel = cast<Instruction>(BitCast.getOperand(0));
+  Value *X;
+  if (match(TVal, m_OneUse(m_BitCast(m_Value(X)))) && X->getType() == DestTy &&
+      !isa<Constant>(X)) {
+    // bitcast(select(Cond, bitcast(X), Y)) --> select'(Cond, X, bitcast(Y))
+    Value *CastedVal = Builder.CreateBitCast(FVal, DestTy);
+    return SelectInst::Create(Cond, X, CastedVal, "", nullptr, Sel);
+  }
+
+  if (match(FVal, m_OneUse(m_BitCast(m_Value(X)))) && X->getType() == DestTy &&
+      !isa<Constant>(X)) {
+    // bitcast(select(Cond, Y, bitcast(X))) --> select'(Cond, bitcast(Y), X)
+    Value *CastedVal = Builder.CreateBitCast(TVal, DestTy);
+    return SelectInst::Create(Cond, CastedVal, X, "", nullptr, Sel);
+  }
+
+  return nullptr;
+}
+
+/// Check if all users of CI are StoreInsts.
+static bool hasStoreUsersOnly(CastInst &CI) {
+  for (User *U : CI.users()) {
+    if (!isa<StoreInst>(U))
+      return false;
+  }
+  return true;
+}
+
+/// This function handles following case
+///
+///     A  ->  B    cast
+///     PHI
+///     B  ->  A    cast
+///
+/// All the related PHI nodes can be replaced by new PHI nodes with type A.
+/// The uses of \p CI can be changed to the new PHI node corresponding to \p PN.
+Instruction *InstCombiner::optimizeBitCastFromPhi(CastInst &CI, PHINode *PN) {
+  // BitCast used by Store can be handled in InstCombineLoadStoreAlloca.cpp.
+  if (hasStoreUsersOnly(CI))
+    return nullptr;
+
+  Value *Src = CI.getOperand(0);
+  Type *SrcTy = Src->getType();         // Type B
+  Type *DestTy = CI.getType();          // Type A
+
+  SmallVector<PHINode *, 4> PhiWorklist;
+  SmallSetVector<PHINode *, 4> OldPhiNodes;
+
+  // Find all of the A->B casts and PHI nodes.
+  // We need to inpect all related PHI nodes, but PHIs can be cyclic, so
+  // OldPhiNodes is used to track all known PHI nodes, before adding a new
+  // PHI to PhiWorklist, it is checked against and added to OldPhiNodes first.
+  PhiWorklist.push_back(PN);
+  OldPhiNodes.insert(PN);
+  while (!PhiWorklist.empty()) {
+    auto *OldPN = PhiWorklist.pop_back_val();
+    for (Value *IncValue : OldPN->incoming_values()) {
+      if (isa<Constant>(IncValue))
+        continue;
+
+      if (auto *LI = dyn_cast<LoadInst>(IncValue)) {
+        // If there is a sequence of one or more load instructions, each loaded
+        // value is used as address of later load instruction, bitcast is
+        // necessary to change the value type, don't optimize it. For
+        // simplicity we give up if the load address comes from another load.
+        Value *Addr = LI->getOperand(0);
+        if (Addr == &CI || isa<LoadInst>(Addr))
+          return nullptr;
+        if (LI->hasOneUse() && LI->isSimple())
+          continue;
+        // If a LoadInst has more than one use, changing the type of loaded
+        // value may create another bitcast.
+        return nullptr;
+      }
+
+      if (auto *PNode = dyn_cast<PHINode>(IncValue)) {
+        if (OldPhiNodes.insert(PNode))
+          PhiWorklist.push_back(PNode);
+        continue;
+      }
+
+      auto *BCI = dyn_cast<BitCastInst>(IncValue);
+      // We can't handle other instructions.
+      if (!BCI)
+        return nullptr;
+
+      // Verify it's a A->B cast.
+      Type *TyA = BCI->getOperand(0)->getType();
+      Type *TyB = BCI->getType();
+      if (TyA != DestTy || TyB != SrcTy)
+        return nullptr;
+    }
+  }
+
+  // For each old PHI node, create a corresponding new PHI node with a type A.
+  SmallDenseMap<PHINode *, PHINode *> NewPNodes;
+  for (auto *OldPN : OldPhiNodes) {
+    Builder->SetInsertPoint(OldPN);
+    PHINode *NewPN = Builder->CreatePHI(DestTy, OldPN->getNumOperands());
+    NewPNodes[OldPN] = NewPN;
+  }
+
+  // Fill in the operands of new PHI nodes.
+  for (auto *OldPN : OldPhiNodes) {
+    PHINode *NewPN = NewPNodes[OldPN];
+    for (unsigned j = 0, e = OldPN->getNumOperands(); j != e; ++j) {
+      Value *V = OldPN->getOperand(j);
+      Value *NewV = nullptr;
+      if (auto *C = dyn_cast<Constant>(V)) {
+        NewV = ConstantExpr::getBitCast(C, DestTy);
+      } else if (auto *LI = dyn_cast<LoadInst>(V)) {
+        Builder->SetInsertPoint(LI->getNextNode());
+        NewV = Builder->CreateBitCast(LI, DestTy);
+        Worklist.Add(LI);
+      } else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
+        NewV = BCI->getOperand(0);
+      } else if (auto *PrevPN = dyn_cast<PHINode>(V)) {
+        NewV = NewPNodes[PrevPN];
+      }
+      assert(NewV);
+      NewPN->addIncoming(NewV, OldPN->getIncomingBlock(j));
+    }
+  }
+
+  // If there is a store with type B, change it to type A.
+  for (User *U : PN->users()) {
+    auto *SI = dyn_cast<StoreInst>(U);
+    if (SI && SI->isSimple() && SI->getOperand(0) == PN) {
+      Builder->SetInsertPoint(SI);
+      auto *NewBC =
+          cast<BitCastInst>(Builder->CreateBitCast(NewPNodes[PN], SrcTy));
+      SI->setOperand(0, NewBC);
+      Worklist.Add(SI);
+      assert(hasStoreUsersOnly(*NewBC));
+    }
+  }
+
+  return replaceInstUsesWith(CI, NewPNodes[PN]);
+}
+
 Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
   // If the operands are integer typed then apply the integer transforms,
   // otherwise just apply the common ones.
@@ -1912,9 +2112,20 @@ Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
     }
   }
 
+  // Handle the A->B->A cast, and there is an intervening PHI node.
+  if (PHINode *PN = dyn_cast<PHINode>(Src))
+    if (Instruction *I = optimizeBitCastFromPhi(CI, PN))
+      return I;
+
   if (Instruction *I = canonicalizeBitCastExtElt(CI, *this, DL))
     return I;
 
+  if (Instruction *I = foldBitCastBitwiseLogic(CI, *Builder))
+    return I;
+
+  if (Instruction *I = foldBitCastSelect(CI, *Builder))
+    return I;
+
   if (SrcTy->isPointerTy())
     return commonPointerCastTransforms(CI);
   return commonCastTransforms(CI);