[MC] Add support for encoding CodeView variable definition ranges

CodeView, like most other debug formats, represents the live range of a
variable so that debuggers might print them out.

They use a variety of records to represent how a particular variable
might be available (in a register, in a frame pointer, etc.) along with
a set of ranges where this debug information is relevant.

However, the format only allows us to use ranges which are limited to a
maximum of 0xF000 in size.  This means that we need to split our debug
information into chunks of 0xF000.

Because the layout of code is not known until *very* late, we must use a
new fragment to record the information we need until we can know
*exactly* what the range is.

llvm-svn: 259868

1 files changed, 27 insertions, 5 deletions

diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 9a55ef3..ca8ccb4 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -303,6 +303,8 @@ uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
   case MCFragment::FT_CVInlineLines:
     return cast<MCCVInlineLineTableFragment>(F).getContents().size();
+  case MCFragment::FT_CVDefRange:
+    return cast<MCCVDefRangeFragment>(F).getContents().size();
   case MCFragment::FT_Dummy:
     llvm_unreachable("Should not have been added");
   }
@@ -545,6 +547,11 @@ static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
     OW->writeBytes(OF.getContents());
     break;
   }
+  case MCFragment::FT_CVDefRange: {
+    const auto &DRF = cast<MCCVDefRangeFragment>(F);
+    OW->writeBytes(DRF.getContents());
+    break;
+  }
   case MCFragment::FT_Dummy:
     llvm_unreachable("Should not have been added");
   }
@@ -673,19 +680,24 @@ void MCAssembler::layout(MCAsmLayout &Layout) {
   // Evaluate and apply the fixups, generating relocation entries as necessary.
   for (MCSection &Sec : *this) {
     for (MCFragment &Frag : Sec) {
-      MCEncodedFragment *F = dyn_cast<MCEncodedFragment>(&Frag);
       // Data and relaxable fragments both have fixups.  So only process
       // those here.
       // FIXME: Is there a better way to do this?  MCEncodedFragmentWithFixups
       // being templated makes this tricky.
-      if (!F || isa<MCCompactEncodedInstFragment>(F))
+      if (isa<MCEncodedFragment>(&Frag) &&
+          isa<MCCompactEncodedInstFragment>(&Frag))
+        continue;
+      if (!isa<MCEncodedFragment>(&Frag) && !isa<MCCVDefRangeFragment>(&Frag))
         continue;
       ArrayRef<MCFixup> Fixups;
       MutableArrayRef<char> Contents;
-      if (auto *FragWithFixups = dyn_cast<MCDataFragment>(F)) {
+      if (auto *FragWithFixups = dyn_cast<MCDataFragment>(&Frag)) {
+        Fixups = FragWithFixups->getFixups();
+        Contents = FragWithFixups->getContents();
+      } else if (auto *FragWithFixups = dyn_cast<MCRelaxableFragment>(&Frag)) {
         Fixups = FragWithFixups->getFixups();
         Contents = FragWithFixups->getContents();
-      } else if (auto *FragWithFixups = dyn_cast<MCRelaxableFragment>(F)) {
+      } else if (auto *FragWithFixups = dyn_cast<MCCVDefRangeFragment>(&Frag)) {
         Fixups = FragWithFixups->getFixups();
         Contents = FragWithFixups->getContents();
       } else
@@ -693,7 +705,7 @@ void MCAssembler::layout(MCAsmLayout &Layout) {
       for (const MCFixup &Fixup : Fixups) {
         uint64_t FixedValue;
         bool IsPCRel;
-        std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
+        std::tie(FixedValue, IsPCRel) = handleFixup(Layout, Frag, Fixup);
         getBackend().applyFixup(Fixup, Contents.data(),
                                 Contents.size(), FixedValue, IsPCRel);
       }
@@ -828,6 +840,13 @@ bool MCAssembler::relaxCVInlineLineTable(MCAsmLayout &Layout,
   return OldSize != F.getContents().size();
 }
 
+bool MCAssembler::relaxCVDefRange(MCAsmLayout &Layout,
+                                  MCCVDefRangeFragment &F) {
+  unsigned OldSize = F.getContents().size();
+  getContext().getCVContext().encodeDefRange(Layout, F);
+  return OldSize != F.getContents().size();
+}
+
 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
   // Holds the first fragment which needed relaxing during this layout. It will
   // remain NULL if none were relaxed.
@@ -863,6 +882,9 @@ bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
       RelaxedFrag =
           relaxCVInlineLineTable(Layout, *cast<MCCVInlineLineTableFragment>(I));
       break;
+    case MCFragment::FT_CVDefRange:
+      RelaxedFrag = relaxCVDefRange(Layout, *cast<MCCVDefRangeFragment>(I));
+      break;
     }
     if (RelaxedFrag && !FirstRelaxedFragment)
       FirstRelaxedFragment = &*I;