Fix PR18743.

The IR
@foo = private constant i32 42

is valid, but before this patch we would produce an invalid MachO from it. It
was invalid because it would use an L label in a section where the liker needs
the labels in order to atomize it.

One way of fixing it would be to just reject this IR in the backend, but that
would not be very front end friendly.

What this patch does is use an 'l' prefix in sections that we know the linker
requires symbols for atomizing them. This allows frontends to just use
private and not worry about which sections they go to or how the linker handles
them.

One small issue with this strategy is that now a symbol name depends on the
section, which is not available before codegen. This is not a problem in
practice. The reason is that it only happens with private linkage, which will
be ignored by the non codegen users (llvm-nm and llvm-ar).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201608 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 28 insertions, 0 deletions

diff --git a/lib/CodeGen/TargetLoweringBase.cpp b/lib/CodeGen/TargetLoweringBase.cpp
index bdcb7216a5..a0ea3b3ba3 100644
--- a/lib/CodeGen/TargetLoweringBase.cpp
+++ b/lib/CodeGen/TargetLoweringBase.cpp
@@ -24,7 +24,9 @@
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/Mangler.h"
 #include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -1426,3 +1428,29 @@ bool TargetLoweringBase::isLegalAddressingMode(const AddrMode &AM,
 
   return true;
 }
+
+void TargetLoweringBase::getNameWithPrefix(SmallVectorImpl<char> &Name,
+                                           const GlobalValue *GV,
+                                           Mangler &Mang) const {
+  if (!GV->hasPrivateLinkage()) {
+    // Simple case: If GV is not private, it is not important to find out if
+    // private labels are legal in this case or not.
+    Mang.getNameWithPrefix(Name, GV, false);
+    return;
+  }
+  SectionKind GVKind =
+    TargetLoweringObjectFile::getKindForGlobal(GV, getTargetMachine());
+  const TargetLoweringObjectFile &TLOF = getObjFileLowering();
+  const MCSection *TheSection =
+    TLOF.SectionForGlobal(GV, GVKind, Mang, getTargetMachine());
+  bool CannotUsePrivateLabel = TLOF.isSectionAtomizableBySymbols(*TheSection);
+  Mang.getNameWithPrefix(Name, GV, CannotUsePrivateLabel);
+}
+
+MCSymbol *TargetLoweringBase::getSymbol(const GlobalValue *GV,
+                                        Mangler &Mang) const {
+  SmallString<60> NameStr;
+  getNameWithPrefix(NameStr, GV, Mang);
+  const TargetLoweringObjectFile &TLOF = getObjFileLowering();
+  return TLOF.getContext().GetOrCreateSymbol(NameStr.str());
+}