[lld] r256693 - Revert or r256638. I`ve lost a little piece of code when resolved conflicts right before commit. Sorry about that.

[George Rimar via llvm-commits]

Author: grimar
Date: Sat Jan  2 10:55:01 2016
New Revision: 256693

URL: http://llvm.org/viewvc/llvm-project?rev=256693&view=rev
Log:
Revert or r256638. I`ve lost a little piece of code when resolved conflicts right before commit. Sorry about that.
Test did not catch this either, so I`ll improve it and recommit later.

Original commit message:
[ELF] - Optimize .eh_frame section: remove CIE if all FDEs referencing it were removed.

This patch performs little optimization for eh_frame section.
If all FDE`s that referenced CIE are removed then CIE is also removed from output. 
That can happen for example when dropping FDEs that point to dropped sections. Testcase showing that is included.
The same optimization was added to ld about 14 years ago: https://sourceware.org/ml/binutils/2001-12/msg00144.html, gold does not do that it seems.

Differential revision: http://reviews.llvm.org/D15564

Removed:
    lld/trunk/test/ELF/eh-frame-opt.s
Modified:
    lld/trunk/ELF/OutputSections.cpp

Modified: lld/trunk/ELF/OutputSections.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=256693&r1=256692&r2=256693&view=diff
==============================================================================
--- lld/trunk/ELF/OutputSections.cpp (original)
+++ lld/trunk/ELF/OutputSections.cpp Sat Jan  2 10:55:01 2016
@@ -947,8 +947,7 @@ void EHOutputSection<ELFT>::addSectionAu
   auto RelI = Rels.begin();
   auto RelE = Rels.end();
 
-  // Maps offset to Index/Length pair.
-  DenseMap<unsigned, std::pair<unsigned, uint32_t>> OffsetToData;
+  DenseMap<unsigned, unsigned> OffsetToIndex;
   while (!D.empty()) {
     unsigned Index = S->Offsets.size();
     S->Offsets.push_back(std::make_pair(Offset, -1));
@@ -975,24 +974,21 @@ void EHOutputSection<ELFT>::addSectionAu
 
       std::pair<StringRef, StringRef> CieInfo(Entry, Personality);
       auto P = CieMap.insert(std::make_pair(CieInfo, Cies.size()));
-      if (P.second)
+      if (P.second) {
         Cies.push_back(C);
-      OffsetToData[Offset] = std::make_pair(P.first->second, Length);
+        this->Header.sh_size += RoundUpToAlignment(Length, sizeof(uintX_t));
+      }
+      OffsetToIndex[Offset] = P.first->second;
     } else {
       if (!HasReloc)
         error("FDE doesn't reference another section");
       InputSectionBase<ELFT> *Target = S->getRelocTarget(*RelI);
       if (Target != &InputSection<ELFT>::Discarded && Target->isLive()) {
         uint32_t CieOffset = Offset + 4 - ID;
-        auto I = OffsetToData.find(CieOffset);
-        if (I == OffsetToData.end())
+        auto I = OffsetToIndex.find(CieOffset);
+        if (I == OffsetToIndex.end())
           error("Invalid CIE reference");
-        std::pair<unsigned, uint32_t> &IndLen = I->second;
-        Cie<ELFT> &Cie = Cies[IndLen.first];
-        if (Cie.Fdes.empty())
-          this->Header.sh_size +=
-              RoundUpToAlignment(IndLen.second, sizeof(uintX_t));
-        Cie.Fdes.push_back(EHRegion<ELFT>(S, Index));
+        Cies[I->second].Fdes.push_back(EHRegion<ELFT>(S, Index));
         this->Header.sh_size += RoundUpToAlignment(Length, sizeof(uintX_t));
       }
     }

Removed: lld/trunk/test/ELF/eh-frame-opt.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/eh-frame-opt.s?rev=256692&view=auto
==============================================================================
--- lld/trunk/test/ELF/eh-frame-opt.s (original)
+++ lld/trunk/test/ELF/eh-frame-opt.s (removed)
@@ -1,39 +0,0 @@
-// REQUIRES: x86
-// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
-// RUN: ld.lld --gc-sections %t.o -o %t
-// RUN: llvm-readobj -s -section-data %t | FileCheck %s
-
-// Here we check that if all FDEs referencing a CIE
-// were removed, CIE is also removed.
-// CHECK:        Section {
-// CHECK:        Index:
-// CHECK:        Name: .eh_frame
-// CHECK-NEXT:   Type: SHT_X86_64_UNWIND
-// CHECK-NEXT:   Flags [
-// CHECK-NEXT:     SHF_ALLOC
-// CHECK-NEXT:   ]
-// CHECK-NEXT:   Address: 0x10120
-// CHECK-NEXT:   Offset: 0x120
-// CHECK-NEXT:   Size: 0
-// CHECK-NEXT:   Link: 0
-// CHECK-NEXT:   Info: 0
-// CHECK-NEXT:   AddressAlignment: 8
-// CHECK-NEXT:   EntrySize: 0
-// CHECK-NEXT:   SectionData (
-// CHECK-NEXT:   )
-// CHECK-NEXT: }
-
-.section foo,"ax", at progbits
-.cfi_startproc
- nop
-.cfi_endproc
-
-.section bar,"ax", at progbits
-.cfi_startproc
- nop
- nop
-.cfi_endproc
-
-.text
-.globl _start;
-_start: