[BOLT] Fix debug info update for zero-length ranges.

Summary:
Due to a clowntown on my part we were generating wrong ranges
when an empty range was seen on input. We were basically expanding
the range to include all basic blocks following such range and setting
wrong sizes at the same time.

Add "-dump-cu" option to llvm-dwarfdump that allows to look at debug
info of a single compile unit only. Saves time if we are only interested
in a subset of information.

(cherry picked from FBD4430989)

bolt/DebugData.cpp

@@ -18,6 +18,9 @@
 #include <algorithm>
 #include <cassert>
 
+#undef  DEBUG_TYPE
+#define DEBUG_TYPE "bolt-debug-info"
+
 namespace opts {
 extern llvm::cl::opt<unsigned> Verbosity;
 }
@@ -31,11 +34,18 @@ void BasicBlockOffsetRanges::addAddressRange(BinaryFunction &Function,
                                              uint64_t BeginAddress,
                                              uint64_t EndAddress,
                                              const BinaryData *Data) {
-  auto BBRange = Function.getBasicBlockRangeFromOffsetToEnd(
-    BeginAddress - Function.getAddress());
+  if (Function.getState() != BinaryFunction::State::CFG)
+    return;
+
+  const auto BBRange = Function.getBasicBlockRangeFromOffsetToEnd(
+                                          BeginAddress - Function.getAddress());
+
+  DEBUG(dbgs() << "adding range [0x" << Twine::utohexstr(BeginAddress) << ", 0x"
+               << Twine::utohexstr(EndAddress) << ") to function " << Function
+               << '\n');
 
   if (BBRange.begin() == BBRange.end()) {
-    if (opts::Verbosity >= 2) {
+    if (opts::Verbosity >= 1) {
       errs() << "BOLT-WARNING: no basic blocks in function "
              << Function << " intersect with debug range [0x"
              << Twine::utohexstr(BeginAddress) << ", 0x"
@@ -45,19 +55,21 @@ void BasicBlockOffsetRanges::addAddressRange(BinaryFunction &Function,
   }
 
   for (auto &BB : BBRange) {
-    uint64_t BBAddress = Function.getBasicBlockOriginalAddress(&BB);
-    // Note the special handling for [a, a) address range.
-    if (BBAddress >= EndAddress && BeginAddress != EndAddress)
+    const auto BBAddress = Function.getBasicBlockOriginalAddress(&BB);
+
+    // Some ranges could be of the form [BBAddress, BBAddress).
+    if (BBAddress > EndAddress ||
+        (BBAddress == EndAddress && EndAddress != BeginAddress))
       break;
 
-    uint64_t InternalAddressRangeBegin = std::max(BBAddress, BeginAddress);
-    assert(BB.getFunction() == &Function &&
-           "Mismatching functions.\n");
-    uint64_t InternalAddressRangeEnd =
+    const auto InternalAddressRangeBegin = std::max(BBAddress, BeginAddress);
+    assert(BB.getFunction() == &Function && "mismatching functions\n");
+    const auto InternalAddressRangeEnd =
       std::min(BBAddress + Function.getBasicBlockOriginalSize(&BB),
                EndAddress);
 
-    assert(BB.isValid() && "Attempting to record debug info for a deleted BB.");
+    assert(BB.isValid() && "attempting to record debug info for a deleted BB.");
+
     AddressRanges.emplace_back(
         BBAddressRange{
             &BB,

bolt/DebugData.h

@@ -22,6 +22,8 @@
 #include <utility>
 #include <vector>
 
+#include "BinaryBasicBlock.h"
+
 namespace llvm {
 
 class DWARFCompileUnit;
@@ -107,6 +109,12 @@ class BasicBlockOffsetRanges {
     uint16_t RangeEndOffset;
     /// Binary data associated with this range.
     const BinaryData *Data;
+
+    void print(raw_ostream &OS) const {
+      OS << "  BasicBlock : " << BasicBlock->getName() << '\n';
+      OS << "  StartOffset: " << RangeBeginOffset << '\n';
+      OS << "  EndOffset:   " << RangeEndOffset << '\n';
+    }
   };
 
   std::vector<BBAddressRange> AddressRanges;