[BOLT] Calculate input to output address map using BOLTLinker

BOLT uses MCAsmLayout to calculate the output values of basic blocks.
This means output values are calculated based on a pre-linking state and
any changes to symbol values during linking will cause incorrect values
to be used.

This issue was first addressed in D154604 by adding all basic block
symbols to the symbol table for the linker to resolve them. However, the
runtime overhead of handling this huge symbol table turned out to be
prohibitively large.

This patch solves the issue in a different way. First, a temporary
section containing [input address, output symbol] pairs is emitted to the
intermediary object file. The linker will resolve all these references
so we end up with a section of [input address, output address] pairs.
This section is then parsed and used to:
- Replace BinaryBasicBlock::OffsetTranslationTable
- Replace BinaryFunction::InputOffsetToAddressMap
- Update BinaryBasicBlock::OutputAddressRange

Note that the reason this is more performant than the previous attempt
is that these symbol references do not cause entries to be added to the
symbol table. Instead, section-relative references are used for the
relocations.

Reviewed By: maksfb

Differential Revision: https://reviews.llvm.org/D155604

bolt/lib/Profile/BoltAddressTranslation.cpp

@@ -46,9 +46,14 @@ void BoltAddressTranslation::writeEntriesForBB(MapTy &Map,
   // allowing it to overwrite the previously inserted key in the map.
   Map[BBOutputOffset] = BBInputOffset;
 
-  for (const auto &IOPair : BB.getOffsetTranslationTable()) {
-    const uint64_t OutputOffset = IOPair.first + BBOutputOffset;
-    const uint32_t InputOffset = IOPair.second;
+  const auto &IOAddressMap =
+      BB.getFunction()->getBinaryContext().getIOAddressMap();
+
+  for (const auto &[InputOffset, Sym] : BB.getLocSyms()) {
+    const auto InputAddress = BB.getFunction()->getAddress() + InputOffset;
+    const auto OutputAddress = IOAddressMap.lookup(InputAddress);
+    assert(OutputAddress && "Unknown instruction address");
+    const auto OutputOffset = *OutputAddress - FuncAddress;
 
     // Is this the first instruction in the BB? No need to duplicate the entry.
     if (OutputOffset == BBOutputOffset)