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

1 files changed, 274 insertions, 49 deletions

diff --git a/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index e0bb0eb..0e478ba 100644
--- a/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -96,8 +96,10 @@
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/ValueHandle.h"
@@ -127,6 +129,26 @@ static cl::opt<unsigned> NumFunctionsForSanityCheck(
              "'0' disables this check. Works only with '-debug' key."),
     cl::init(0), cl::Hidden);
 
+// Under option -mergefunc-preserve-debug-info we:
+// - Do not create a new function for a thunk.
+// - Retain the debug info for a thunk's parameters (and associated
+//   instructions for the debug info) from the entry block.
+//   Note: -debug will display the algorithm at work.
+// - Create debug-info for the call (to the shared implementation) made by
+//   a thunk and its return value.
+// - Erase the rest of the function, retaining the (minimally sized) entry
+//   block to create a thunk.
+// - Preserve a thunk's call site to point to the thunk even when both occur
+//   within the same translation unit, to aid debugability. Note that this
+//   behaviour differs from the underlying -mergefunc implementation which
+//   modifies the thunk's call site to point to the shared implementation
+//   when both occur within the same translation unit.
+static cl::opt<bool>
+    MergeFunctionsPDI("mergefunc-preserve-debug-info", cl::Hidden,
+                      cl::init(false),
+                      cl::desc("Preserve debug info in thunk when mergefunc "
+                               "transformations are made."));
+
 namespace {
 
 class FunctionNode {
@@ -185,11 +207,13 @@ private:
 
   /// A work queue of functions that may have been modified and should be
   /// analyzed again.
-  std::vector<WeakVH> Deferred;
+  std::vector<WeakTrackingVH> Deferred;
 
   /// Checks the rules of order relation introduced among functions set.
   /// Returns true, if sanity check has been passed, and false if failed.
-  bool doSanityCheck(std::vector<WeakVH> &Worklist);
+#ifndef NDEBUG
+  bool doSanityCheck(std::vector<WeakTrackingVH> &Worklist);
+#endif
 
   /// Insert a ComparableFunction into the FnTree, or merge it away if it's
   /// equal to one that's already present.
@@ -215,8 +239,21 @@ private:
   /// Replace G with a thunk or an alias to F. Deletes G.
   void writeThunkOrAlias(Function *F, Function *G);
 
-  /// Replace G with a simple tail call to bitcast(F). Also replace direct uses
-  /// of G with bitcast(F). Deletes G.
+  /// Fill PDIUnrelatedWL with instructions from the entry block that are
+  /// unrelated to parameter related debug info.
+  void filterInstsUnrelatedToPDI(BasicBlock *GEntryBlock,
+                                 std::vector<Instruction *> &PDIUnrelatedWL);
+
+  /// Erase the rest of the CFG (i.e. barring the entry block).
+  void eraseTail(Function *G);
+
+  /// Erase the instructions in PDIUnrelatedWL as they are unrelated to the
+  /// parameter debug info, from the entry block.
+  void eraseInstsUnrelatedToPDI(std::vector<Instruction *> &PDIUnrelatedWL);
+
+  /// Replace G with a simple tail call to bitcast(F). Also (unless
+  /// MergeFunctionsPDI holds) replace direct uses of G with bitcast(F),
+  /// delete G.
   void writeThunk(Function *F, Function *G);
 
   /// Replace G with an alias to F. Deletes G.
@@ -248,7 +285,8 @@ ModulePass *llvm::createMergeFunctionsPass() {
   return new MergeFunctions();
 }
 
-bool MergeFunctions::doSanityCheck(std::vector<WeakVH> &Worklist) {
+#ifndef NDEBUG
+bool MergeFunctions::doSanityCheck(std::vector<WeakTrackingVH> &Worklist) {
   if (const unsigned Max = NumFunctionsForSanityCheck) {
     unsigned TripleNumber = 0;
     bool Valid = true;
@@ -256,10 +294,12 @@ bool MergeFunctions::doSanityCheck(std::vector<WeakVH> &Worklist) {
     dbgs() << "MERGEFUNC-SANITY: Started for first " << Max << " functions.\n";
 
     unsigned i = 0;
-    for (std::vector<WeakVH>::iterator I = Worklist.begin(), E = Worklist.end();
+    for (std::vector<WeakTrackingVH>::iterator I = Worklist.begin(),
+                                               E = Worklist.end();
          I != E && i < Max; ++I, ++i) {
       unsigned j = i;
-      for (std::vector<WeakVH>::iterator J = I; J != E && j < Max; ++J, ++j) {
+      for (std::vector<WeakTrackingVH>::iterator J = I; J != E && j < Max;
+           ++J, ++j) {
         Function *F1 = cast<Function>(*I);
         Function *F2 = cast<Function>(*J);
         int Res1 = FunctionComparator(F1, F2, &GlobalNumbers).compare();
@@ -269,8 +309,7 @@ bool MergeFunctions::doSanityCheck(std::vector<WeakVH> &Worklist) {
         if (Res1 != -Res2) {
           dbgs() << "MERGEFUNC-SANITY: Non-symmetric; triple: " << TripleNumber
                  << "\n";
-          F1->dump();
-          F2->dump();
+          dbgs() << *F1 << '\n' << *F2 << '\n';
           Valid = false;
         }
 
@@ -278,7 +317,7 @@ bool MergeFunctions::doSanityCheck(std::vector<WeakVH> &Worklist) {
           continue;
 
         unsigned k = j;
-        for (std::vector<WeakVH>::iterator K = J; K != E && k < Max;
+        for (std::vector<WeakTrackingVH>::iterator K = J; K != E && k < Max;
              ++k, ++K, ++TripleNumber) {
           if (K == J)
             continue;
@@ -305,9 +344,7 @@ bool MergeFunctions::doSanityCheck(std::vector<WeakVH> &Worklist) {
                    << TripleNumber << "\n";
             dbgs() << "Res1, Res3, Res4: " << Res1 << ", " << Res3 << ", "
                    << Res4 << "\n";
-            F1->dump();
-            F2->dump();
-            F3->dump();
+            dbgs() << *F1 << '\n' << *F2 << '\n' << *F3 << '\n';
             Valid = false;
           }
         }
@@ -319,6 +356,7 @@ bool MergeFunctions::doSanityCheck(std::vector<WeakVH> &Worklist) {
   }
   return true;
 }
+#endif
 
 bool MergeFunctions::runOnModule(Module &M) {
   if (skipModule(M))
@@ -349,12 +387,12 @@ bool MergeFunctions::runOnModule(Module &M) {
     // consider merging it. Otherwise it is dropped and never considered again.
     if ((I != S && std::prev(I)->first == I->first) ||
         (std::next(I) != IE && std::next(I)->first == I->first) ) {
-      Deferred.push_back(WeakVH(I->second));
+      Deferred.push_back(WeakTrackingVH(I->second));
     }
   }
   
   do {
-    std::vector<WeakVH> Worklist;
+    std::vector<WeakTrackingVH> Worklist;
     Deferred.swap(Worklist);
 
     DEBUG(doSanityCheck(Worklist));
@@ -363,7 +401,7 @@ bool MergeFunctions::runOnModule(Module &M) {
     DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n');
 
     // Insert functions and merge them.
-    for (WeakVH &I : Worklist) {
+    for (WeakTrackingVH &I : Worklist) {
       if (!I)
         continue;
       Function *F = cast<Function>(I);
@@ -400,19 +438,15 @@ void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) {
       // Transferring other attributes may help other optimizations, but that
       // should be done uniformly and not in this ad-hoc way.
       auto &Context = New->getContext();
-      auto NewFuncAttrs = New->getAttributes();
-      auto CallSiteAttrs = CS.getAttributes();
-
-      CallSiteAttrs = CallSiteAttrs.addAttributes(
-          Context, AttributeSet::ReturnIndex, NewFuncAttrs.getRetAttributes());
-
-      for (unsigned argIdx = 0; argIdx < CS.arg_size(); argIdx++) {
-        AttributeSet Attrs = NewFuncAttrs.getParamAttributes(argIdx);
-        if (Attrs.getNumSlots())
-          CallSiteAttrs = CallSiteAttrs.addAttributes(Context, argIdx, Attrs);
-      }
-
-      CS.setAttributes(CallSiteAttrs);
+      auto NewPAL = New->getAttributes();
+      SmallVector<AttributeSet, 4> NewArgAttrs;
+      for (unsigned argIdx = 0; argIdx < CS.arg_size(); argIdx++)
+        NewArgAttrs.push_back(NewPAL.getParamAttributes(argIdx));
+      // Don't transfer attributes from the function to the callee. Function
+      // attributes typically aren't relevant to the calling convention or ABI.
+      CS.setAttributes(AttributeList::get(Context, /*FnAttrs=*/AttributeSet(),
+                                          NewPAL.getRetAttributes(),
+                                          NewArgAttrs));
 
       remove(CS.getInstruction()->getParent()->getParent());
       U->set(BitcastNew);
@@ -461,51 +495,242 @@ static Value *createCast(IRBuilder<> &Builder, Value *V, Type *DestTy) {
     return Builder.CreateBitCast(V, DestTy);
 }
 
-// Replace G with a simple tail call to bitcast(F). Also replace direct uses
-// of G with bitcast(F). Deletes G.
+// Erase the instructions in PDIUnrelatedWL as they are unrelated to the
+// parameter debug info, from the entry block.
+void MergeFunctions::eraseInstsUnrelatedToPDI(
+    std::vector<Instruction *> &PDIUnrelatedWL) {
+
+  DEBUG(dbgs() << " Erasing instructions (in reverse order of appearance in "
+                  "entry block) unrelated to parameter debug info from entry "
+                  "block: {\n");
+  while (!PDIUnrelatedWL.empty()) {
+    Instruction *I = PDIUnrelatedWL.back();
+    DEBUG(dbgs() << "  Deleting Instruction: ");
+    DEBUG(I->print(dbgs()));
+    DEBUG(dbgs() << "\n");
+    I->eraseFromParent();
+    PDIUnrelatedWL.pop_back();
+  }
+  DEBUG(dbgs() << " } // Done erasing instructions unrelated to parameter "
+                  "debug info from entry block. \n");
+}
+
+// Reduce G to its entry block.
+void MergeFunctions::eraseTail(Function *G) {
+
+  std::vector<BasicBlock *> WorklistBB;
+  for (Function::iterator BBI = std::next(G->begin()), BBE = G->end();
+       BBI != BBE; ++BBI) {
+    BBI->dropAllReferences();
+    WorklistBB.push_back(&*BBI);
+  }
+  while (!WorklistBB.empty()) {
+    BasicBlock *BB = WorklistBB.back();
+    BB->eraseFromParent();
+    WorklistBB.pop_back();
+  }
+}
+
+// We are interested in the following instructions from the entry block as being
+// related to parameter debug info:
+// - @llvm.dbg.declare
+// - stores from the incoming parameters to locations on the stack-frame
+// - allocas that create these locations on the stack-frame
+// - @llvm.dbg.value
+// - the entry block's terminator
+// The rest are unrelated to debug info for the parameters; fill up
+// PDIUnrelatedWL with such instructions.
+void MergeFunctions::filterInstsUnrelatedToPDI(
+    BasicBlock *GEntryBlock, std::vector<Instruction *> &PDIUnrelatedWL) {
+
+  std::set<Instruction *> PDIRelated;
+  for (BasicBlock::iterator BI = GEntryBlock->begin(), BIE = GEntryBlock->end();
+       BI != BIE; ++BI) {
+    if (auto *DVI = dyn_cast<DbgValueInst>(&*BI)) {
+      DEBUG(dbgs() << " Deciding: ");
+      DEBUG(BI->print(dbgs()));
+      DEBUG(dbgs() << "\n");
+      DILocalVariable *DILocVar = DVI->getVariable();
+      if (DILocVar->isParameter()) {
+        DEBUG(dbgs() << "  Include (parameter): ");
+        DEBUG(BI->print(dbgs()));
+        DEBUG(dbgs() << "\n");
+        PDIRelated.insert(&*BI);
+      } else {
+        DEBUG(dbgs() << "  Delete (!parameter): ");
+        DEBUG(BI->print(dbgs()));
+        DEBUG(dbgs() << "\n");
+      }
+    } else if (auto *DDI = dyn_cast<DbgDeclareInst>(&*BI)) {
+      DEBUG(dbgs() << " Deciding: ");
+      DEBUG(BI->print(dbgs()));
+      DEBUG(dbgs() << "\n");
+      DILocalVariable *DILocVar = DDI->getVariable();
+      if (DILocVar->isParameter()) {
+        DEBUG(dbgs() << "  Parameter: ");
+        DEBUG(DILocVar->print(dbgs()));
+        AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
+        if (AI) {
+          DEBUG(dbgs() << "  Processing alloca users: ");
+          DEBUG(dbgs() << "\n");
+          for (User *U : AI->users()) {
+            if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
+              if (Value *Arg = SI->getValueOperand()) {
+                if (dyn_cast<Argument>(Arg)) {
+                  DEBUG(dbgs() << "  Include: ");
+                  DEBUG(AI->print(dbgs()));
+                  DEBUG(dbgs() << "\n");
+                  PDIRelated.insert(AI);
+                  DEBUG(dbgs() << "   Include (parameter): ");
+                  DEBUG(SI->print(dbgs()));
+                  DEBUG(dbgs() << "\n");
+                  PDIRelated.insert(SI);
+                  DEBUG(dbgs() << "  Include: ");
+                  DEBUG(BI->print(dbgs()));
+                  DEBUG(dbgs() << "\n");
+                  PDIRelated.insert(&*BI);
+                } else {
+                  DEBUG(dbgs() << "   Delete (!parameter): ");
+                  DEBUG(SI->print(dbgs()));
+                  DEBUG(dbgs() << "\n");
+                }
+              }
+            } else {
+              DEBUG(dbgs() << "   Defer: ");
+              DEBUG(U->print(dbgs()));
+              DEBUG(dbgs() << "\n");
+            }
+          }
+        } else {
+          DEBUG(dbgs() << "  Delete (alloca NULL): ");
+          DEBUG(BI->print(dbgs()));
+          DEBUG(dbgs() << "\n");
+        }
+      } else {
+        DEBUG(dbgs() << "  Delete (!parameter): ");
+        DEBUG(BI->print(dbgs()));
+        DEBUG(dbgs() << "\n");
+      }
+    } else if (dyn_cast<TerminatorInst>(BI) == GEntryBlock->getTerminator()) {
+      DEBUG(dbgs() << " Will Include Terminator: ");
+      DEBUG(BI->print(dbgs()));
+      DEBUG(dbgs() << "\n");
+      PDIRelated.insert(&*BI);
+    } else {
+      DEBUG(dbgs() << " Defer: ");
+      DEBUG(BI->print(dbgs()));
+      DEBUG(dbgs() << "\n");
+    }
+  }
+  DEBUG(dbgs()
+        << " Report parameter debug info related/related instructions: {\n");
+  for (BasicBlock::iterator BI = GEntryBlock->begin(), BE = GEntryBlock->end();
+       BI != BE; ++BI) {
+
+    Instruction *I = &*BI;
+    if (PDIRelated.find(I) == PDIRelated.end()) {
+      DEBUG(dbgs() << "  !PDIRelated: ");
+      DEBUG(I->print(dbgs()));
+      DEBUG(dbgs() << "\n");
+      PDIUnrelatedWL.push_back(I);
+    } else {
+      DEBUG(dbgs() << "   PDIRelated: ");
+      DEBUG(I->print(dbgs()));
+      DEBUG(dbgs() << "\n");
+    }
+  }
+  DEBUG(dbgs() << " }\n");
+}
+
+// Replace G with a simple tail call to bitcast(F). Also (unless
+// MergeFunctionsPDI holds) replace direct uses of G with bitcast(F),
+// delete G. Under MergeFunctionsPDI, we use G itself for creating
+// the thunk as we preserve the debug info (and associated instructions)
+// from G's entry block pertaining to G's incoming arguments which are
+// passed on as corresponding arguments in the call that G makes to F.
+// For better debugability, under MergeFunctionsPDI, we do not modify G's
+// call sites to point to F even when within the same translation unit.
 void MergeFunctions::writeThunk(Function *F, Function *G) {
-  if (!G->isInterposable()) {
-    // Redirect direct callers of G to F.
+  if (!G->isInterposable() && !MergeFunctionsPDI) {
+    // Redirect direct callers of G to F. (See note on MergeFunctionsPDI
+    // above).
     replaceDirectCallers(G, F);
   }
 
   // If G was internal then we may have replaced all uses of G with F. If so,
-  // stop here and delete G. There's no need for a thunk.
-  if (G->hasLocalLinkage() && G->use_empty()) {
+  // stop here and delete G. There's no need for a thunk. (See note on
+  // MergeFunctionsPDI above).
+  if (G->hasLocalLinkage() && G->use_empty() && !MergeFunctionsPDI) {
     G->eraseFromParent();
     return;
   }
 
-  Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
-                                    G->getParent());
-  BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG);
-  IRBuilder<> Builder(BB);
+  BasicBlock *GEntryBlock = nullptr;
+  std::vector<Instruction *> PDIUnrelatedWL;
+  BasicBlock *BB = nullptr;
+  Function *NewG = nullptr;
+  if (MergeFunctionsPDI) {
+    DEBUG(dbgs() << "writeThunk: (MergeFunctionsPDI) Do not create a new "
+                    "function as thunk; retain original: "
+                 << G->getName() << "()\n");
+    GEntryBlock = &G->getEntryBlock();
+    DEBUG(dbgs() << "writeThunk: (MergeFunctionsPDI) filter parameter related "
+                    "debug info for "
+                 << G->getName() << "() {\n");
+    filterInstsUnrelatedToPDI(GEntryBlock, PDIUnrelatedWL);
+    GEntryBlock->getTerminator()->eraseFromParent();
+    BB = GEntryBlock;
+  } else {
+    NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
+                            G->getParent());
+    BB = BasicBlock::Create(F->getContext(), "", NewG);
+  }
 
+  IRBuilder<> Builder(BB);
+  Function *H = MergeFunctionsPDI ? G : NewG;
   SmallVector<Value *, 16> Args;
   unsigned i = 0;
   FunctionType *FFTy = F->getFunctionType();
-  for (Argument & AI : NewG->args()) {
+  for (Argument & AI : H->args()) {
     Args.push_back(createCast(Builder, &AI, FFTy->getParamType(i)));
     ++i;
   }
 
   CallInst *CI = Builder.CreateCall(F, Args);
+  ReturnInst *RI = nullptr;
   CI->setTailCall();
   CI->setCallingConv(F->getCallingConv());
   CI->setAttributes(F->getAttributes());
-  if (NewG->getReturnType()->isVoidTy()) {
-    Builder.CreateRetVoid();
+  if (H->getReturnType()->isVoidTy()) {
+    RI = Builder.CreateRetVoid();
   } else {
-    Builder.CreateRet(createCast(Builder, CI, NewG->getReturnType()));
+    RI = Builder.CreateRet(createCast(Builder, CI, H->getReturnType()));
   }
 
-  NewG->copyAttributesFrom(G);
-  NewG->takeName(G);
-  removeUsers(G);
-  G->replaceAllUsesWith(NewG);
-  G->eraseFromParent();
+  if (MergeFunctionsPDI) {
+    DISubprogram *DIS = G->getSubprogram();
+    if (DIS) {
+      DebugLoc CIDbgLoc = DebugLoc::get(DIS->getScopeLine(), 0, DIS);
+      DebugLoc RIDbgLoc = DebugLoc::get(DIS->getScopeLine(), 0, DIS);
+      CI->setDebugLoc(CIDbgLoc);
+      RI->setDebugLoc(RIDbgLoc);
+    } else {
+      DEBUG(dbgs() << "writeThunk: (MergeFunctionsPDI) No DISubprogram for "
+                   << G->getName() << "()\n");
+    }
+    eraseTail(G);
+    eraseInstsUnrelatedToPDI(PDIUnrelatedWL);
+    DEBUG(dbgs() << "} // End of parameter related debug info filtering for: "
+                 << G->getName() << "()\n");
+  } else {
+    NewG->copyAttributesFrom(G);
+    NewG->takeName(G);
+    removeUsers(G);
+    G->replaceAllUsesWith(NewG);
+    G->eraseFromParent();
+  }
 
-  DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n');
+  DEBUG(dbgs() << "writeThunk: " << H->getName() << '\n');
   ++NumThunksWritten;
 }