Merge clang, llvm, lld, lldb, compiler-rt and libc++ 5.0.0 release.

MFC r309126 (by emaste):

  Correct lld llvm-tblgen dependency file name

MFC r309169:

  Get rid of separate Subversion mergeinfo properties for llvm-dwarfdump
  and llvm-lto.  The mergeinfo confuses Subversion enormously, and these
  directories will just use the mergeinfo for llvm itself.

MFC r312765:

  Pull in r276136 from upstream llvm trunk (by Wei Mi):

    Use ValueOffsetPair to enhance value reuse during SCEV expansion.

    In D12090, the ExprValueMap was added to reuse existing value during
    SCEV expansion. However, const folding and sext/zext distribution can
    make the reuse still difficult.

    A simplified case is: suppose we know S1 expands to V1 in
    ExprValueMap, and
      S1 = S2 + C_a
      S3 = S2 + C_b
    where C_a and C_b are different SCEVConstants. Then we'd like to
    expand S3 as V1 - C_a + C_b instead of expanding S2 literally. It is
    helpful when S2 is a complex SCEV expr and S2 has no entry in
    ExprValueMap, which is usually caused by the fact that S3 is
    generated from S1 after const folding.

    In order to do that, we represent ExprValueMap as a mapping from SCEV
    to ValueOffsetPair. We will save both S1->{V1, 0} and S2->{V1, C_a}
    into the ExprValueMap when we create SCEV for V1. When S3 is
    expanded, it will first expand S2 to V1 - C_a because of S2->{V1,
    C_a} in the map, then expand S3 to V1 - C_a + C_b.

    Differential Revision: https://reviews.llvm.org/D21313

  This should fix assertion failures when building OpenCV >= 3.1.

  PR:		215649

MFC r312831:

  Revert r312765 for now, since it causes assertions when building
  lang/spidermonkey24.

  Reported by:	antoine
  PR:		215649

MFC r316511 (by jhb):

  Add an implementation of __ffssi2() derived from __ffsdi2().

  Newer versions of GCC include an __ffssi2() symbol in libgcc and the
  compiler can emit calls to it in generated code.  This is true for at
  least GCC 6.2 when compiling world for mips and mips64.

  Reviewed by:	jmallett, dim
  Sponsored by:	DARPA / AFRL
  Differential Revision:	https://reviews.freebsd.org/D10086

MFC r318601 (by adrian):

  [libcompiler-rt] add bswapdi2/bswapsi2

  This is required for mips gcc 6.3 userland to build/run.

  Reviewed by:	emaste, dim
  Approved by:	emaste
  Differential Revision:	https://reviews.freebsd.org/D10838

MFC r318884 (by emaste):

  lldb: map TRAP_CAP to a trace trap

  In the absense of a more specific handler for TRAP_CAP (generated by
  ENOTCAPABLE or ECAPMODE while in capability mode) treat it as a trace
  trap.

  Example usage (testing the bug in PR219173):

  % proccontrol -m trapcap lldb usr.bin/hexdump/obj/hexdump -- -Cv -s 1 /bin/ls
  ...
  (lldb) run
  Process 12980 launching
  Process 12980 launched: '.../usr.bin/hexdump/obj/hexdump' (x86_64)
  Process 12980 stopped
  * thread #1, stop reason = trace
      frame #0: 0x0000004b80c65f1a libc.so.7`__sys_lseek + 10
  ...

  In the future we should have LLDB control the trapcap procctl itself
  (as it does with ASLR), as well as report a specific stop reason.
  This change eliminates an assertion failure from LLDB for now.

MFC r319796:

  Remove a few unneeded files from libllvm, libclang and liblldb.

MFC r319885 (by emaste):

  lld: ELF: Fix ICF crash on absolute symbol relocations.

  If two sections contained relocations to absolute symbols with the same
  value we would crash when trying to access their sections. Add a check that
  both symbols point to sections before accessing their sections, and treat
  absolute symbols as equal if their values are equal.

  Obtained from:	LLD commit r292578

MFC r319918:

  Revert r319796 for now, it can cause undefined references when linking
  in some circumstances.

  Reported by:	Shawn Webb <shawn.webb@hardenedbsd.org>

MFC r319957 (by emaste):

  lld: Add armelf emulation mode

  Obtained from:	LLD r305375

MFC r321369:

  Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
  5.0.0 (trunk r308421).  Upstream has branched for the 5.0.0 release,
  which should be in about a month.  Please report bugs and regressions,
  so we can get them into the release.

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

MFC r321420:

  Add a few more object files to liblldb, which should solve errors when
  linking the lldb executable in some cases.  In particular, when the
  -ffunction-sections -fdata-sections options are turned off, or
  ineffective.

  Reported by:	Shawn Webb, Mark Millard

MFC r321433:

  Cleanup stale Options.inc files from the previous libllvm build for
  clang 4.0.0.  Otherwise, these can get included before the two newly
  generated ones (which are different) for clang 5.0.0.

  Reported by:	Mark Millard

MFC r321439 (by bdrewery):

  Move llvm Options.inc hack from r321433 for NO_CLEAN to lib/clang/libllvm.

  The files are only ever generated to .OBJDIR, not to WORLDTMP (as a
  sysroot) and are only ever included from a compilation.  So using
  a beforebuild target here removes the file before the compilation
  tries to include it.

MFC r321664:

  Pull in r308891 from upstream llvm trunk (by Benjamin Kramer):

    [CodeGenPrepare] Cut off FindAllMemoryUses if there are too many uses.

    This avoids excessive compile time. The case I'm looking at is
    Function.cpp from an old version of LLVM that still had the giant
    memcmp string matcher in it. Before r308322 this compiled in about 2
    minutes, after it, clang takes infinite* time to compile it. With
    this patch we're at 5 min, which is still bad but this is a
    pathological case.

    The cut off at 20 uses was chosen by looking at other cut-offs in LLVM
    for user scanning. It's probably too high, but does the job and is
    very unlikely to regress anything.

    Fixes PR33900.

    * I'm impatient and aborted after 15 minutes, on the bug report it was
      killed after 2h.

  Pull in r308986 from upstream llvm trunk (by Simon Pilgrim):

    [X86][CGP] Reduce memcmp() expansion to 2 load pairs (PR33914)

    D35067/rL308322 attempted to support up to 4 load pairs for memcmp
    inlining which resulted in regressions for some optimized libc memcmp
    implementations (PR33914).

    Until we can match these more optimal cases, this patch reduces the
    memcmp expansion to a maximum of 2 load pairs (which matches what we
    do for -Os).

    This patch should be considered for the 5.0.0 release branch as well

    Differential Revision: https://reviews.llvm.org/D35830

  These fix a hang (or extremely long compile time) when building older
  LLVM ports.

  Reported by:    antoine
  PR:             219139

MFC r321719:

  Pull in r309503 from upstream clang trunk (by Richard Smith):

    PR33902: Invalidate line number cache when adding more text to
    existing buffer.

    This led to crashes as the line number cache would report a bogus
    line number for a line of code, and we'd try to find a nonexistent
    column within the line when printing diagnostics.

  This fixes an assertion when building the graphics/champlain port.

  Reported by:	antoine, kwm
  PR:		219139

MFC r321723:

  Upgrade our copies of clang, llvm, lld and lldb to r309439 from the
  upstream release_50 branch.  This is just after upstream's 5.0.0-rc1.

MFC r322320:

  Upgrade our copies of clang, llvm and libc++ to r310316 from the
  upstream release_50 branch.

MFC r322326 (by emaste):

  lldb: Make i386-*-freebsd expression work on JIT path

  * Enable i386 ABI creation for freebsd
  * Added an extra argument in ABISysV_i386::PrepareTrivialCall for mmap
    syscall
  * Unlike linux, the last argument of mmap is actually 64-bit(off_t).
    This requires us to push an additional word for the higher order bits.
  * Prior to this change, ktrace dump will show mmap failures due to
    invalid argument coming from the 6th mmap argument.

  Submitted by:	Karnajit Wangkhem
  Differential Revision:	https://reviews.llvm.org/D34776

MFC r322360 (by emaste):

  lldb: Report inferior signals as signals, not exceptions, on FreeBSD

  This is the FreeBSD equivalent of LLVM r238549.

  This serves 2 purposes:

  * LLDB should handle inferior process signals SIGSEGV/SIGILL/SIGBUS/
    SIGFPE the way it is suppose to be handled. Prior to this fix these
    signals will neither create a coredump, nor exit from the debugger
    or work for signal handling scenario.
  * eInvalidCrashReason need not report "unknown crash reason" if we have
    a valid si_signo

  llvm.org/pr23699

  Patch by Karnajit Wangkhem

  Differential Revision:  https://reviews.llvm.org/D35223

  Submitted by:	Karnajit Wangkhem
  Obtained from:	LLVM r310591

MFC r322474 (by emaste):

  lld: Add `-z muldefs` option.

  Obtained from:	LLVM r310757

MFC r322740:

  Upgrade our copies of clang, llvm, lld and libc++ to r311219 from the
  upstream release_50 branch.

MFC r322855:

  Upgrade our copies of clang, llvm, lldb and compiler-rt to r311606 from
  the upstream release_50 branch.

  As of this version, lib/msun's trig test should also work correctly
  again (see bug 220989 for more information).

  PR:		220989

MFC r323112:

  Upgrade our copies of clang, llvm, lldb and compiler-rt to r312293 from
  the upstream release_50 branch.  This corresponds to 5.0.0 rc4.

  As of this version, the cad/stepcode port should now compile in a more
  reasonable time on i386 (see bug 221836 for more information).

  PR:		221836

MFC r323245:

  Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
  5.0.0 release (upstream r312559).

  Release notes for llvm, clang and lld will be available here soon:
  <http://releases.llvm.org/5.0.0/docs/ReleaseNotes.html>
  <http://releases.llvm.org/5.0.0/tools/clang/docs/ReleaseNotes.html>
  <http://releases.llvm.org/5.0.0/tools/lld/docs/ReleaseNotes.html>

  Relnotes:	yes

(cherry picked from commit 12cd91cf4c6b96a24427c0de5374916f2808d263)

1 files changed, 181 insertions, 64 deletions

diff --git a/contrib/llvm/lib/CodeGen/BranchFolding.cpp b/contrib/llvm/lib/CodeGen/BranchFolding.cpp
index 6fba161..3c439e6 100644
--- a/contrib/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/contrib/llvm/lib/CodeGen/BranchFolding.cpp
@@ -1,4 +1,4 @@
-//===-- BranchFolding.cpp - Fold machine code branch instructions ---------===//
+//===- BranchFolding.cpp - Fold machine code branch instructions ----------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -18,37 +18,55 @@
 //===----------------------------------------------------------------------===//
 
 #include "BranchFolding.h"
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/CodeGen/Analysis.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
-#include "llvm/CodeGen/MachineMemOperand.h"
 #include "llvm/CodeGen/MachineLoopInfo.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineOperand.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
-#include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Function.h"
+#include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/BlockFrequency.h"
+#include "llvm/Support/BranchProbability.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
-#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <iterator>
+#include <numeric>
+#include <vector>
+
 using namespace llvm;
 
-#define DEBUG_TYPE "branchfolding"
+#define DEBUG_TYPE "branch-folder"
 
 STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
 STATISTIC(NumBranchOpts, "Number of branches optimized");
 STATISTIC(NumTailMerge , "Number of block tails merged");
 STATISTIC(NumHoist     , "Number of times common instructions are hoisted");
+STATISTIC(NumTailCalls,  "Number of tail calls optimized");
 
 static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
                               cl::init(cl::BOU_UNSET), cl::Hidden);
@@ -67,10 +85,12 @@ TailMergeSize("tail-merge-size",
                               cl::init(3), cl::Hidden);
 
 namespace {
+
   /// BranchFolderPass - Wrap branch folder in a machine function pass.
   class BranchFolderPass : public MachineFunctionPass {
   public:
     static char ID;
+
     explicit BranchFolderPass(): MachineFunctionPass(ID) {}
 
     bool runOnMachineFunction(MachineFunction &MF) override;
@@ -82,12 +102,13 @@ namespace {
       MachineFunctionPass::getAnalysisUsage(AU);
     }
   };
-}
+
+} // end anonymous namespace
 
 char BranchFolderPass::ID = 0;
 char &llvm::BranchFolderPassID = BranchFolderPass::ID;
 
-INITIALIZE_PASS(BranchFolderPass, "branch-folder",
+INITIALIZE_PASS(BranchFolderPass, DEBUG_TYPE,
                 "Control Flow Optimizer", false, false)
 
 bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) {
@@ -123,8 +144,6 @@ BranchFolder::BranchFolder(bool defaultEnableTailMerge, bool CommonHoist,
   }
 }
 
-/// RemoveDeadBlock - Remove the specified dead machine basic block from the
-/// function, updating the CFG.
 void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
   assert(MBB->pred_empty() && "MBB must be dead!");
   DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
@@ -144,9 +163,6 @@ void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
     MLI->removeBlock(MBB);
 }
 
-/// OptimizeFunction - Perhaps branch folding, tail merging and other
-/// CFG optimizations on the given function.  Block placement changes the layout
-/// and may create new tail merging opportunities.
 bool BranchFolder::OptimizeFunction(MachineFunction &MF,
                                     const TargetInstrInfo *tii,
                                     const TargetRegisterInfo *tri,
@@ -156,13 +172,14 @@ bool BranchFolder::OptimizeFunction(MachineFunction &MF,
 
   TriedMerging.clear();
 
+  MachineRegisterInfo &MRI = MF.getRegInfo();
   AfterBlockPlacement = AfterPlacement;
   TII = tii;
   TRI = tri;
   MMI = mmi;
   MLI = mli;
+  this->MRI = &MRI;
 
-  MachineRegisterInfo &MRI = MF.getRegInfo();
   UpdateLiveIns = MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF);
   if (!UpdateLiveIns)
     MRI.invalidateLiveness();
@@ -348,23 +365,18 @@ static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
   return TailLen;
 }
 
-/// ReplaceTailWithBranchTo - Delete the instruction OldInst and everything
-/// after it, replacing it with an unconditional branch to NewDest.
 void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
                                            MachineBasicBlock *NewDest) {
   TII->ReplaceTailWithBranchTo(OldInst, NewDest);
 
   if (UpdateLiveIns) {
     NewDest->clearLiveIns();
-    computeLiveIns(LiveRegs, *TRI, *NewDest);
+    computeLiveIns(LiveRegs, *MRI, *NewDest);
   }
 
   ++NumTailMerge;
 }
 
-/// SplitMBBAt - Given a machine basic block and an iterator into it, split the
-/// MBB so that the part before the iterator falls into the part starting at the
-/// iterator.  This returns the new MBB.
 MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
                                             MachineBasicBlock::iterator BBI1,
                                             const BasicBlock *BB) {
@@ -375,7 +387,7 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
 
   // Create the fall-through block.
   MachineFunction::iterator MBBI = CurMBB.getIterator();
-  MachineBasicBlock *NewMBB =MF.CreateMachineBasicBlock(BB);
+  MachineBasicBlock *NewMBB = MF.CreateMachineBasicBlock(BB);
   CurMBB.getParent()->insert(++MBBI, NewMBB);
 
   // Move all the successors of this block to the specified block.
@@ -388,7 +400,7 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
   NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end());
 
   // NewMBB belongs to the same loop as CurMBB.
-  if (MLI) 
+  if (MLI)
     if (MachineLoop *ML = MLI->getLoopFor(&CurMBB))
       ML->addBasicBlockToLoop(NewMBB, MLI->getBase());
 
@@ -396,7 +408,7 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
   MBBFreqInfo.setBlockFreq(NewMBB, MBBFreqInfo.getBlockFreq(&CurMBB));
 
   if (UpdateLiveIns)
-    computeLiveIns(LiveRegs, *TRI, *NewMBB);
+    computeLiveIns(LiveRegs, *MRI, *NewMBB);
 
   // Add the new block to the funclet.
   const auto &FuncletI = FuncletMembership.find(&CurMBB);
@@ -436,7 +448,7 @@ static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB,
   MachineFunction::iterator I = std::next(MachineFunction::iterator(CurMBB));
   MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
   SmallVector<MachineOperand, 4> Cond;
-  DebugLoc dl;  // FIXME: this is nowhere
+  DebugLoc dl = CurMBB->findBranchDebugLoc();
   if (I != MF->end() && !TII->analyzeBranch(*CurMBB, TBB, FBB, Cond, true)) {
     MachineBasicBlock *NextBB = &*I;
     if (TBB == NextBB && !Cond.empty() && !FBB) {
@@ -497,6 +509,15 @@ BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
   return MBFI.printBlockFreq(OS, Freq);
 }
 
+void BranchFolder::MBFIWrapper::view(const Twine &Name, bool isSimple) {
+  MBFI.view(Name, isSimple);
+}
+
+uint64_t
+BranchFolder::MBFIWrapper::getEntryFreq() const {
+  return MBFI.getEntryFreq();
+}
+
 /// CountTerminators - Count the number of terminators in the given
 /// block and set I to the position of the first non-terminator, if there
 /// is one, or MBB->end() otherwise.
@@ -504,7 +525,7 @@ static unsigned CountTerminators(MachineBasicBlock *MBB,
                                  MachineBasicBlock::iterator &I) {
   I = MBB->end();
   unsigned NumTerms = 0;
-  for (;;) {
+  while (true) {
     if (I == MBB->begin()) {
       I = MBB->end();
       break;
@@ -516,6 +537,17 @@ static unsigned CountTerminators(MachineBasicBlock *MBB,
   return NumTerms;
 }
 
+/// A no successor, non-return block probably ends in unreachable and is cold.
+/// Also consider a block that ends in an indirect branch to be a return block,
+/// since many targets use plain indirect branches to return.
+static bool blockEndsInUnreachable(const MachineBasicBlock *MBB) {
+  if (!MBB->succ_empty())
+    return false;
+  if (MBB->empty())
+    return true;
+  return !(MBB->back().isReturn() || MBB->back().isIndirectBranch());
+}
+
 /// ProfitableToMerge - Check if two machine basic blocks have a common tail
 /// and decide if it would be profitable to merge those tails.  Return the
 /// length of the common tail and iterators to the first common instruction
@@ -570,6 +602,15 @@ ProfitableToMerge(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2,
       return true;
   }
 
+  // If these are identical non-return blocks with no successors, merge them.
+  // Such blocks are typically cold calls to noreturn functions like abort, and
+  // are unlikely to become a fallthrough target after machine block placement.
+  // Tail merging these blocks is unlikely to create additional unconditional
+  // branches, and will reduce the size of this cold code.
+  if (I1 == MBB1->begin() && I2 == MBB2->begin() &&
+      blockEndsInUnreachable(MBB1) && blockEndsInUnreachable(MBB2))
+    return true;
+
   // If one of the blocks can be completely merged and happens to be in
   // a position where the other could fall through into it, merge any number
   // of instructions, because it can be done without a branch.
@@ -579,6 +620,22 @@ ProfitableToMerge(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2,
   if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin())
     return true;
 
+  // If both blocks are identical and end in a branch, merge them unless they
+  // both have a fallthrough predecessor and successor.
+  // We can only do this after block placement because it depends on whether
+  // there are fallthroughs, and we don't know until after layout.
+  if (AfterPlacement && I1 == MBB1->begin() && I2 == MBB2->begin()) {
+    auto BothFallThrough = [](MachineBasicBlock *MBB) {
+      if (MBB->succ_size() != 0 && !MBB->canFallThrough())
+        return false;
+      MachineFunction::iterator I(MBB);
+      MachineFunction *MF = MBB->getParent();
+      return (MBB != &*MF->begin()) && std::prev(I)->canFallThrough();
+    };
+    if (!BothFallThrough(MBB1) || !BothFallThrough(MBB2))
+      return true;
+  }
+
   // If both blocks have an unconditional branch temporarily stripped out,
   // count that as an additional common instruction for the following
   // heuristics. This heuristic is only accurate for single-succ blocks, so to
@@ -604,16 +661,6 @@ ProfitableToMerge(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2,
          (I1 == MBB1->begin() || I2 == MBB2->begin());
 }
 
-/// ComputeSameTails - Look through all the blocks in MergePotentials that have
-/// hash CurHash (guaranteed to match the last element).  Build the vector
-/// SameTails of all those that have the (same) largest number of instructions
-/// in common of any pair of these blocks.  SameTails entries contain an
-/// iterator into MergePotentials (from which the MachineBasicBlock can be
-/// found) and a MachineBasicBlock::iterator into that MBB indicating the
-/// instruction where the matching code sequence begins.
-/// Order of elements in SameTails is the reverse of the order in which
-/// those blocks appear in MergePotentials (where they are not necessarily
-/// consecutive).
 unsigned BranchFolder::ComputeSameTails(unsigned CurHash,
                                         unsigned MinCommonTailLength,
                                         MachineBasicBlock *SuccBB,
@@ -650,8 +697,6 @@ unsigned BranchFolder::ComputeSameTails(unsigned CurHash,
   return maxCommonTailLength;
 }
 
-/// RemoveBlocksWithHash - Remove all blocks with hash CurHash from
-/// MergePotentials, restoring branches at ends of blocks as appropriate.
 void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
                                         MachineBasicBlock *SuccBB,
                                         MachineBasicBlock *PredBB) {
@@ -671,8 +716,6 @@ void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
   MergePotentials.erase(CurMPIter, MergePotentials.end());
 }
 
-/// CreateCommonTailOnlyBlock - None of the blocks to be tail-merged consist
-/// only of the common tail.  Create a block that does by splitting one.
 bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
                                              MachineBasicBlock *SuccBB,
                                              unsigned maxCommonTailLength,
@@ -723,6 +766,43 @@ bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
   return true;
 }
 
+void BranchFolder::MergeCommonTailDebugLocs(unsigned commonTailIndex) {
+  MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
+
+  std::vector<MachineBasicBlock::iterator> NextCommonInsts(SameTails.size());
+  for (unsigned int i = 0 ; i != SameTails.size() ; ++i) {
+    if (i != commonTailIndex)
+      NextCommonInsts[i] = SameTails[i].getTailStartPos();
+    else {
+      assert(SameTails[i].getTailStartPos() == MBB->begin() &&
+          "MBB is not a common tail only block");
+    }
+  }
+
+  for (auto &MI : *MBB) {
+    if (MI.isDebugValue())
+      continue;
+    DebugLoc DL = MI.getDebugLoc();
+    for (unsigned int i = 0 ; i < NextCommonInsts.size() ; i++) {
+      if (i == commonTailIndex)
+        continue;
+
+      auto &Pos = NextCommonInsts[i];
+      assert(Pos != SameTails[i].getBlock()->end() &&
+          "Reached BB end within common tail");
+      while (Pos->isDebugValue()) {
+        ++Pos;
+        assert(Pos != SameTails[i].getBlock()->end() &&
+            "Reached BB end within common tail");
+      }
+      assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!");
+      DL = DILocation::getMergedLocation(DL, Pos->getDebugLoc());
+      NextCommonInsts[i] = ++Pos;
+    }
+    MI.setDebugLoc(DL);
+  }
+}
+
 static void
 mergeOperations(MachineBasicBlock::iterator MBBIStartPos,
                 MachineBasicBlock &MBBCommon) {
@@ -875,10 +955,8 @@ bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
     // Recompute common tail MBB's edge weights and block frequency.
     setCommonTailEdgeWeights(*MBB);
 
-    // Remove the original debug location from the common tail.
-    for (auto &MI : *MBB)
-      if (!MI.isDebugValue())
-        MI.setDebugLoc(DebugLoc());
+    // Merge debug locations across identical instructions for common tail.
+    MergeCommonTailDebugLocs(commonTailIndex);
 
     // MBB is common tail.  Adjust all other BB's to jump to this one.
     // Traversal must be forwards so erases work.
@@ -1043,7 +1121,7 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
 
         // Remove the unconditional branch at the end, if any.
         if (TBB && (Cond.empty() || FBB)) {
-          DebugLoc dl;  // FIXME: this is nowhere
+          DebugLoc dl = PBB->findBranchDebugLoc();
           TII->removeBranch(*PBB);
           if (!Cond.empty())
             // reinsert conditional branch only, for now
@@ -1193,8 +1271,6 @@ static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) {
   return DebugLoc();
 }
 
-/// OptimizeBlock - Analyze and optimize control flow related to the specified
-/// block.  This is never called on the entry block.
 bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
   bool MadeChange = false;
   MachineFunction &MF = *MBB->getParent();
@@ -1386,6 +1462,43 @@ ReoptimizeBlock:
     }
   }
 
+  if (!IsEmptyBlock(MBB) && MBB->pred_size() == 1 &&
+      MF.getFunction()->optForSize()) {
+    // Changing "Jcc foo; foo: jmp bar;" into "Jcc bar;" might change the branch
+    // direction, thereby defeating careful block placement and regressing
+    // performance. Therefore, only consider this for optsize functions.
+    MachineInstr &TailCall = *MBB->getFirstNonDebugInstr();
+    if (TII->isUnconditionalTailCall(TailCall)) {
+      MachineBasicBlock *Pred = *MBB->pred_begin();
+      MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
+      SmallVector<MachineOperand, 4> PredCond;
+      bool PredAnalyzable =
+          !TII->analyzeBranch(*Pred, PredTBB, PredFBB, PredCond, true);
+
+      if (PredAnalyzable && !PredCond.empty() && PredTBB == MBB &&
+          PredTBB != PredFBB) {
+        // The predecessor has a conditional branch to this block which consists
+        // of only a tail call. Try to fold the tail call into the conditional
+        // branch.
+        if (TII->canMakeTailCallConditional(PredCond, TailCall)) {
+          // TODO: It would be nice if analyzeBranch() could provide a pointer
+          // to the branch instruction so replaceBranchWithTailCall() doesn't
+          // have to search for it.
+          TII->replaceBranchWithTailCall(*Pred, PredCond, TailCall);
+          ++NumTailCalls;
+          Pred->removeSuccessor(MBB);
+          MadeChange = true;
+          return MadeChange;
+        }
+      }
+      // If the predecessor is falling through to this block, we could reverse
+      // the branch condition and fold the tail call into that. However, after
+      // that we might have to re-arrange the CFG to fall through to the other
+      // block and there is a high risk of regressing code size rather than
+      // improving it.
+    }
+  }
+
   // Analyze the branch in the current block.
   MachineBasicBlock *CurTBB = nullptr, *CurFBB = nullptr;
   SmallVector<MachineOperand, 4> CurCond;
@@ -1508,7 +1621,6 @@ ReoptimizeBlock:
   // block doesn't fall through into some other block, see if we can find a
   // place to move this block where a fall-through will happen.
   if (!PrevBB.canFallThrough()) {
-
     // Now we know that there was no fall-through into this block, check to
     // see if it has a fall-through into its successor.
     bool CurFallsThru = MBB->canFallThrough();
@@ -1599,8 +1711,6 @@ ReoptimizeBlock:
 //  Hoist Common Code
 //===----------------------------------------------------------------------===//
 
-/// HoistCommonCode - Hoist common instruction sequences at the start of basic
-/// blocks to their common predecessor.
 bool BranchFolder::HoistCommonCode(MachineFunction &MF) {
   bool MadeChange = false;
   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ) {
@@ -1734,9 +1844,6 @@ MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB,
   return PI;
 }
 
-/// HoistCommonCodeInSuccs - If the successors of MBB has common instruction
-/// sequence at the start of the function, move the instructions before MBB
-/// terminator if it's legal.
 bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
   MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
   SmallVector<MachineOperand, 4> Cond;
@@ -1763,8 +1870,8 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
     return false;
 
   bool HasDups = false;
-  SmallVector<unsigned, 4> LocalDefs;
-  SmallSet<unsigned, 4> LocalDefsSet;
+  SmallVector<unsigned, 4> LocalDefs, LocalKills;
+  SmallSet<unsigned, 4> ActiveDefsSet, AllDefsSet;
   MachineBasicBlock::iterator TIB = TBB->begin();
   MachineBasicBlock::iterator FIB = FBB->begin();
   MachineBasicBlock::iterator TIE = TBB->end();
@@ -1818,7 +1925,7 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
           IsSafe = false;
           break;
         }
-      } else if (!LocalDefsSet.count(Reg)) {
+      } else if (!ActiveDefsSet.count(Reg)) {
         if (Defs.count(Reg)) {
           // Use is defined by the instruction at the point of insertion.
           IsSafe = false;
@@ -1838,18 +1945,22 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
     if (!TIB->isSafeToMove(nullptr, DontMoveAcrossStore))
       break;
 
-    // Remove kills from LocalDefsSet, these registers had short live ranges.
+    // Remove kills from ActiveDefsSet, these registers had short live ranges.
     for (const MachineOperand &MO : TIB->operands()) {
       if (!MO.isReg() || !MO.isUse() || !MO.isKill())
         continue;
       unsigned Reg = MO.getReg();
-      if (!Reg || !LocalDefsSet.count(Reg))
+      if (!Reg)
         continue;
+      if (!AllDefsSet.count(Reg)) {
+        LocalKills.push_back(Reg);
+        continue;
+      }
       if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
         for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
-          LocalDefsSet.erase(*AI);
+          ActiveDefsSet.erase(*AI);
       } else {
-        LocalDefsSet.erase(Reg);
+        ActiveDefsSet.erase(Reg);
       }
     }
 
@@ -1861,7 +1972,8 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
       if (!Reg || TargetRegisterInfo::isVirtualRegister(Reg))
         continue;
       LocalDefs.push_back(Reg);
-      addRegAndItsAliases(Reg, TRI, LocalDefsSet);
+      addRegAndItsAliases(Reg, TRI, ActiveDefsSet);
+      addRegAndItsAliases(Reg, TRI, AllDefsSet);
     }
 
     HasDups = true;
@@ -1876,17 +1988,22 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
   FBB->erase(FBB->begin(), FIB);
 
   // Update livein's.
-  bool AddedLiveIns = false;
+  bool ChangedLiveIns = false;
   for (unsigned i = 0, e = LocalDefs.size(); i != e; ++i) {
     unsigned Def = LocalDefs[i];
-    if (LocalDefsSet.count(Def)) {
+    if (ActiveDefsSet.count(Def)) {
       TBB->addLiveIn(Def);
       FBB->addLiveIn(Def);
-      AddedLiveIns = true;
+      ChangedLiveIns = true;
     }
   }
+  for (unsigned K : LocalKills) {
+    TBB->removeLiveIn(K);
+    FBB->removeLiveIn(K);
+    ChangedLiveIns = true;
+  }
 
-  if (AddedLiveIns) {
+  if (ChangedLiveIns) {
     TBB->sortUniqueLiveIns();
     FBB->sortUniqueLiveIns();
   }