Remove doesSectionRequireSymbols.

In an assembly expression like

bar:
.long L0 + 1

the intended semantics is that bar will contain a pointer one byte past L0.

In sections that are merged by content (strings, 4 byte constants, etc), a
single position in the section doesn't give the linker enough information.
For example, it would not be able to tell a relocation must point to the
end of a string, since that would look just like the start of the next.

The solution used in ELF to use relocation with symbols if there is a non-zero
addend.

In MachO before this patch we would just keep all symbols in some sections.

This would miss some cases (only cstrings on x86_64 were implemented) and was
inefficient since most relocations have an addend of 0 and can be represented
without the symbol.

This patch implements the non-zero addend logic for MachO too.

llvm-svn: 224985

1 files changed, 14 insertions, 2 deletions

diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 459488bfe15..a4af21efee1 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -425,6 +425,16 @@ bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
   return true;
 }
 
+void MCAssembler::addLocalUsedInReloc(const MCSymbol &Sym) {
+  assert(Sym.isTemporary());
+  LocalsUsedInReloc.insert(&Sym);
+}
+
+bool MCAssembler::isLocalUsedInReloc(const MCSymbol &Sym) const {
+  assert(Sym.isTemporary());
+  return LocalsUsedInReloc.count(&Sym);
+}
+
 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
   // Non-temporary labels should always be visible to the linker.
   if (!Symbol.isTemporary())
@@ -434,8 +444,10 @@ bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
   if (!Symbol.isInSection())
     return false;
 
-  // Otherwise, check if the section requires symbols even for temporary labels.
-  return getBackend().doesSectionRequireSymbols(Symbol.getSection());
+  if (isLocalUsedInReloc(Symbol))
+    return true;
+
+  return false;
 }
 
 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {