[DWARF] Generate DWARF v5 string offsets tables along with strx* index forms.

Summary: This is the producer side for DWARF v5 string offsets tables. The reader/consumer
side was committed with r321295. All compile and type units in a module share a 
contribution to the string offsets table. Indirect strings use the strx{1,2,3,4} index forms.

Reviewers: dblaikie, aprantl, JDevliegehere

Differential Revision: https://reviews.llvm.org/D42021

llvm-svn: 323546

1 files changed, 23 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index 71f452b6d8d..889b1235940 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -241,9 +241,22 @@ void DwarfUnit::addSInt(DIELoc &Die, Optional<dwarf::Form> Form,
 
 void DwarfUnit::addString(DIE &Die, dwarf::Attribute Attribute,
                           StringRef String) {
-  Die.addValue(DIEValueAllocator, Attribute,
-               isDwoUnit() ? dwarf::DW_FORM_GNU_str_index : dwarf::DW_FORM_strp,
-               DIEString(DU->getStringPool().getEntry(*Asm, String)));
+  auto StringPoolEntry = DU->getStringPool().getEntry(*Asm, String);
+  dwarf::Form IxForm =
+      isDwoUnit() ? dwarf::DW_FORM_GNU_str_index : dwarf::DW_FORM_strp;
+  // For DWARF v5 and beyond, use the smallest strx? form possible.
+  if (useSegmentedStringOffsetsTable()) {
+    IxForm = dwarf::DW_FORM_strx1;
+    unsigned Index = StringPoolEntry.getIndex();
+    if (Index > 0xffffff)
+      IxForm = dwarf::DW_FORM_strx4;
+    else if (Index > 0xffff)
+      IxForm = dwarf::DW_FORM_strx3;
+    else if (Index > 0xff)
+      IxForm = dwarf::DW_FORM_strx2;
+  }
+  Die.addValue(DIEValueAllocator, Attribute, IxForm,
+               DIEString(StringPoolEntry));
 }
 
 DIEValueList::value_iterator DwarfUnit::addLabel(DIEValueList &Die,
@@ -1660,3 +1673,10 @@ const MCSymbol *DwarfUnit::getCrossSectionRelativeBaseAddress() const {
     return nullptr;
   return getSection()->getBeginSymbol();
 }
+
+void DwarfUnit::addStringOffsetsStart() {
+  const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
+  addSectionLabel(getUnitDie(), dwarf::DW_AT_str_offsets_base,
+                  DU->getStringOffsetsStartSym(),
+                  TLOF.getDwarfStrOffSection()->getBeginSymbol());
+}