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

This allows the linker to GC both, fixing pr22557.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228937 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/TargetLoweringObjectFileImpl.h

@@ -56,6 +56,10 @@ public:
                                         SectionKind Kind, Mangler &Mang,
                                         const TargetMachine &TM) const override;
 
+  const MCSection *
+  getSectionForJumpTable(const Function &F, Mangler &Mang,
+                         const TargetMachine &TM) const override;
+
   /// Return an MCExpr to use for a reference to the specified type info global
   /// variable from exception handling information.
   const MCExpr *

include/llvm/Target/TargetLoweringObjectFile.h

@@ -94,6 +94,10 @@ public:
     return SectionForGlobal(GV, getKindForGlobal(GV, TM), Mang, TM);
   }
 
+  virtual const MCSection *
+  getSectionForJumpTable(const Function &F, Mangler &Mang,
+                         const TargetMachine &TM) const;
+
   /// Targets should implement this method to assign a section to globals with
   /// an explicit section specfied. The implementation of this method can
   /// assume that GV->hasSection() is true.

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(
+    OutStreamer.SwitchSection(TLOF.SectionForGlobal(F, *Mang, TM));
-        getObjFileLowering().SectionForGlobal(F, *Mang, TM));
   } else {
     // Otherwise, drop it in the readonly section.
     const MCSection *ReadOnlySection =
-        getObjFileLowering().getSectionForConstant(SectionKind::getReadOnly(),
+        TLOF.getSectionForJumpTable(*F, *Mang, TM);
-                                                   /*C=*/nullptr);
     OutStreamer.SwitchSection(ReadOnlySection);
     JTInDiffSection = true;
   }

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.

lib/Target/TargetLoweringObjectFile.cpp

@@ -270,6 +270,11 @@ SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
   return SelectSectionForGlobal(GV, Kind, Mang, TM);
 }
 
+const MCSection *TargetLoweringObjectFile::getSectionForJumpTable(
+    const Function &F, Mangler &Mang, const TargetMachine &TM) const {
+  return getSectionForConstant(SectionKind::getReadOnly(), /*C=*/nullptr);
+}
+
 /// getSectionForConstant - Given a mergable constant with the
 /// specified size and relocation information, return a section that it
 /// should be placed in.

test/CodeGen/X86/global-sections-comdat.ll

@@ -1,5 +1,36 @@
 ; RUN: llc < %s -mtriple=i386-unknown-linux | FileCheck %s -check-prefix=LINUX
-; RUN: llc < %s -mtriple=i386-unknown-linux -data-sections | FileCheck %s -check-prefix=LINUX-SECTIONS
+; RUN: llc < %s -mtriple=i386-unknown-linux -data-sections -function-sections | FileCheck %s -check-prefix=LINUX-SECTIONS
+
+$F1 = comdat any
+define void @F1(i32 %y) comdat {
+bb0:
+switch i32 %y, label %bb5 [
+    i32 1, label %bb1
+    i32 2, label %bb2
+    i32 3, label %bb3
+    i32 4, label %bb4
+  ]
+bb1:
+  ret void
+bb2:
+  ret void
+bb3:
+  ret void
+bb4:
+  ret void
+bb5:
+  ret void
+}
+
+; LINUX: .section        .text.F1,"axG",@progbits,F1,comdat
+; LINUX: .size   F1,
+; LINUX-NEXT: .cfi_endproc
+; LINUX-NEXT: .section        .rodata.F1,"aG",@progbits,F1,comdat
+
+; LINUX-SECTIONS: .section        .text.F1,"axG",@progbits,F1,comdat
+; LINUX-SECTIONS: .size   F1,
+; LINUX-SECTIONS-NEXT: .cfi_endproc
+; LINUX-SECTIONS-NEXT: .section        .rodata.F1,"aG",@progbits,F1,comdat
 
 $G16 = comdat any
 @G16 = unnamed_addr constant i32 42, comdat

test/CodeGen/X86/global-sections.ll

@@ -2,7 +2,7 @@
 ; RUN: llc < %s -mtriple=i386-apple-darwin9.7 | FileCheck %s -check-prefix=DARWIN
 ; RUN: llc < %s -mtriple=i386-apple-darwin10 -relocation-model=static | FileCheck %s -check-prefix=DARWIN-STATIC
 ; RUN: llc < %s -mtriple=x86_64-apple-darwin10 | FileCheck %s -check-prefix=DARWIN64
-; RUN: llc < %s -mtriple=i386-unknown-linux-gnu -data-sections | FileCheck %s -check-prefix=LINUX-SECTIONS
+; RUN: llc < %s -mtriple=i386-unknown-linux-gnu -data-sections -function-sections | FileCheck %s -check-prefix=LINUX-SECTIONS
 ; RUN: llc < %s -mtriple=i686-pc-win32 -data-sections -function-sections | FileCheck %s -check-prefix=WIN32-SECTIONS
 
 define void @F1() {
@@ -12,6 +12,35 @@ define void @F1() {
 ; WIN32-SECTIONS: .section        .text,"xr",one_only,_F1
 ; WIN32-SECTIONS: .globl _F1
 
+define void @F2(i32 %y) {
+bb0:
+switch i32 %y, label %bb5 [
+    i32 1, label %bb1
+    i32 2, label %bb2
+    i32 3, label %bb3
+    i32 4, label %bb4
+  ]
+bb1:
+  ret void
+bb2:
+  ret void
+bb3:
+  ret void
+bb4:
+  ret void
+bb5:
+  ret void
+}
+
+; LINUX:     .size   F2,
+; LINUX-NEX: .cfi_endproc
+; LINUX-NEX: .section        .rodata,"a",@progbits
+
+; LINUX-SECTIONS: .section        .text.F2,"ax",@progbits
+; LINUX-SECTIONS: .size   F2,
+; LINUX-SECTIONS-NEXT: .cfi_endproc
+; LINUX-SECTIONS-NEXT: .section        .rodata.F2,"a",@progbits
+
 ; int G1;
 @G1 = common global i32 0