Put each jump table in an independent section if the function is too.

This allows the linker to GC both, fixing pr22557.

llvm-svn: 228937

2 files changed, 25 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 7fb84605071..aacc486aa14 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1177,6 +1177,7 @@ void AsmPrinter::EmitJumpTableInfo() {
   // Pick the directive to use to print the jump table entries, and switch to
   // the appropriate section.
   const Function *F = MF->getFunction();
+  const TargetLoweringObjectFile &TLOF = getObjFileLowering();
   bool JTInDiffSection = false;
   if (// In PIC mode, we need to emit the jump table to the same section as the
       // function body itself, otherwise the label differences won't make sense.
@@ -1187,13 +1188,11 @@ void AsmPrinter::EmitJumpTableInfo() {
       // FIXME: this isn't the right predicate, should be based on the MCSection
       // for the function.
       F->isWeakForLinker()) {
-    OutStreamer.SwitchSection(
-        getObjFileLowering().SectionForGlobal(F, *Mang, TM));
+    OutStreamer.SwitchSection(TLOF.SectionForGlobal(F, *Mang, TM));
   } else {
     // Otherwise, drop it in the readonly section.
     const MCSection *ReadOnlySection =
-        getObjFileLowering().getSectionForConstant(SectionKind::getReadOnly(),
-                                                   /*C=*/nullptr);
+        TLOF.getSectionForJumpTable(*F, *Mang, TM);
     OutStreamer.SwitchSection(ReadOnlySection);
     JTInDiffSection = true;
   }
diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index eac1245d829..0a49f5ff9fe 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -334,6 +334,28 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
   return DataRelROSection;
 }
 
+const MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
+    const Function &F, Mangler &Mang, const TargetMachine &TM) const {
+  // If the function can be removed, produce a unique section so that
+  // the table doesn't prevent the removal.
+  const Comdat *C = F.getComdat();
+  bool EmitUniqueSection = TM.getFunctionSections() || C;
+  if (!EmitUniqueSection)
+    return ReadOnlySection;
+
+  SmallString<128> Name(".rodata.");
+  TM.getNameWithPrefix(Name, &F, Mang, true);
+
+  unsigned Flags = ELF::SHF_ALLOC;
+  StringRef Group = "";
+  if (C) {
+    Flags |= ELF::SHF_GROUP;
+    Group = C->getName();
+  }
+
+  return getContext().getELFSection(Name, ELF::SHT_PROGBITS, Flags, 0, Group);
+}
+
 /// getSectionForConstant - Given a mergeable constant with the
 /// specified size and relocation information, return a section that it
 /// should be placed in.