ELF: Do not create multiple thunks for the same virtual address.

This avoids creating multiple thunks for symbols with aliases or which
belong to ICF'd sections. This patch reduces the size of Chromium for
Android by 260KB (0.8% of .text).

Differential Revision: https://reviews.llvm.org/D44284

llvm-svn: 327154

diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index bf67e61..c168b01 100644 (file)
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -1240,17 +1240,22 @@ ThunkSection *ThunkCreator::addThunkSection(OutputSection *OS,
 
 std::pair<Thunk *, bool> ThunkCreator::getThunk(Symbol &Sym, RelType Type,
                                                 uint64_t Src) {
-  auto Res = ThunkedSymbols.insert({&Sym, std::vector<Thunk *>()});
-  if (!Res.second) {
-    // Check existing Thunks for Sym to see if they can be reused
-    for (Thunk *ET : Res.first->second)
-      if (ET->isCompatibleWith(Type) &&
-          Target->inBranchRange(Type, Src, ET->ThunkSym->getVA()))
-        return std::make_pair(ET, false);
-  }
+  std::vector<Thunk *> *ThunkVec = nullptr;
+  // We use (section, offset) pair to find the thunk position if possible so
+  // that we create only one thunk for aliased symbols or ICFed sections.
+  if (auto *D = dyn_cast<Defined>(&Sym))
+    if (!D->isInPlt() && D->Section)
+      ThunkVec = &ThunkedSymbolsBySection[{D->Section->Repl, D->Value}];
+  if (!ThunkVec)
+    ThunkVec = &ThunkedSymbols[&Sym];
+  // Check existing Thunks for Sym to see if they can be reused
+  for (Thunk *ET : *ThunkVec)
+    if (ET->isCompatibleWith(Type) &&
+        Target->inBranchRange(Type, Src, ET->ThunkSym->getVA()))
+      return std::make_pair(ET, false);
   // No existing compatible Thunk in range, create a new one
   Thunk *T = addThunk(Type, Sym);
-  Res.first->second.push_back(T);
+  ThunkVec->push_back(T);
   return std::make_pair(T, true);
 }
 

diff --git a/lld/ELF/Relocations.h b/lld/ELF/Relocations.h
index 7b142e1..69afe31 100644 (file)
--- a/lld/ELF/Relocations.h
+++ b/lld/ELF/Relocations.h
@@ -21,7 +21,7 @@ class Symbol;
 class InputSection;
 class InputSectionBase;
 class OutputSection;
-class OutputSection;
+class SectionBase;
 
 // Represents a relocation type, such as R_X86_64_PC32 or R_ARM_THM_CALL.
 typedef uint32_t RelType;
@@ -161,6 +161,8 @@ private:
   bool normalizeExistingThunk(Relocation &Rel, uint64_t Src);
 
   // Record all the available Thunks for a Symbol
+  llvm::DenseMap<std::pair<SectionBase *, uint64_t>, std::vector<Thunk *>>
+      ThunkedSymbolsBySection;
   llvm::DenseMap<Symbol *, std::vector<Thunk *>> ThunkedSymbols;
 
   // Find a Thunk from the Thunks symbol definition, we can use this to find

diff --git a/lld/test/ELF/arm-thumb-plt-range-thunk-os.s b/lld/test/ELF/arm-thumb-plt-range-thunk-os.s
index f412faa..080160b 100644 (file)
--- a/lld/test/ELF/arm-thumb-plt-range-thunk-os.s
+++ b/lld/test/ELF/arm-thumb-plt-range-thunk-os.s
@@ -1,12 +1,12 @@
 // REQUIRES: arm
 // RUN: llvm-mc -filetype=obj -triple=thumbv7a-none-linux-gnueabi %s -o %t
-// RUN: ld.lld %t --shared -o %t.so
+// RUN: ld.lld %t --shared --icf=all -o %t.so
 // The output file is large, most of it zeroes. We dissassemble only the
 // parts we need to speed up the test and avoid a large output file
-// RUN: llvm-objdump -d %t.so -start-address=8388608 -stop-address=8388624 -triple=thumbv7a-linux-gnueabihf | FileCheck -check-prefix=CHECK1 %s
-// RUN: llvm-objdump -d %t.so -start-address=16777216 -stop-address=16777256 -triple=thumbv7a-linux-gnueabihf | FileCheck -check-prefix=CHECK2 %s
-// RUN: llvm-objdump -d %t.so -start-address=25165824 -stop-address=25165828 -triple=thumbv7a-linux-gnueabihf | FileCheck -check-prefix=CHECK3 %s
-// RUN: llvm-objdump -d %t.so -start-address=25165828 -stop-address=25165924 -triple=armv7a-linux-gnueabihf | FileCheck -check-prefix=CHECK4 %s
+// RUN: llvm-objdump -d %t.so -start-address=0x2000000 -stop-address=0x2000018 -triple=thumbv7a-linux-gnueabihf | FileCheck -check-prefix=CHECK1 %s
+// RUN: llvm-objdump -d %t.so -start-address=0x2800004 -stop-address=0x2800034 -triple=thumbv7a-linux-gnueabihf | FileCheck -check-prefix=CHECK2 %s
+// RUN: llvm-objdump -d %t.so -start-address=0x4000000 -stop-address=0x4000010 -triple=thumbv7a-linux-gnueabihf | FileCheck -check-prefix=CHECK3 %s
+// RUN: llvm-objdump -d %t.so -start-address=0x4000010 -stop-address=0x4000100 -triple=armv7a-linux-gnueabihf | FileCheck -check-prefix=CHECK4 %s
  .syntax unified
  .thumb
 
@@ -19,74 +19,96 @@
  .type preemptible, %function
  .global far_preemptible
  .type far_preemptible, %function
+ .global far_nonpreemptible
+ .hidden far_nonpreemptible
+ .type far_nonpreemptible, %function
+ .global far_nonpreemptible_alias
+ .hidden far_nonpreemptible_alias
+ .type far_nonpreemptible_alias, %function
 sym1:
  bl elsewhere
  bl preemptible
  bx lr
 preemptible:
  bl far_preemptible
+ bl far_nonpreemptible
+ bl far_nonpreemptible_alias
  bx lr
 // CHECK1: Disassembly of section .text:
 // CHECK1-NEXT: sym1:
-// CHECK1-NEXT:   800000:       00 f0 00 d8     bl      #8388608
-// CHECK1-NEXT:   800004:       00 f0 04 d8     bl      #8388616
-// CHECK1-NEXT:   800008:       70 47   bx      lr
+// CHECK1-NEXT:  2000000:       00 f0 00 d8     bl      #8388608
+// CHECK1-NEXT:  2000004:       00 f0 04 d8     bl      #8388616
+// CHECK1-NEXT:  2000008:       70 47   bx      lr
 // CHECK1: preemptible:
-// CHECK1-NEXT:   80000a:       00 f0 07 d8     bl      #8388622
-// CHECK1-NEXT:   80000e:       70 47   bx      lr
+// CHECK1-NEXT:  200000a:       00 f0 07 d8     bl      #8388622
+// CHECK1-NEXT:  200000e:       00 f0 0b d8     bl      #8388630
+// CHECK1-NEXT:  2000012:       00 f0 09 d8     bl      #8388626
+// CHECK1-NEXT:  2000016:       70 47   bx      lr
 
  .section .text.2, "ax", %progbits
  .balign 0x0800000
  bx lr
 // CHECK2: __ThumbV7PILongThunk_elsewhere:
-// CHECK2-NEXT:  1000004:       40 f2 20 0c     movw    r12, #32
-// CHECK2-NEXT:  1000008:       c0 f2 80 0c     movt    r12, #128
-// CHECK2-NEXT:  100000c:       fc 44   add     r12, pc
-// CHECK2-NEXT:  100000e:       60 47   bx      r12
+// CHECK2-NEXT:  2800004:       40 f2 20 0c     movw    r12, #32
+// CHECK2-NEXT:  2800008:       c0 f2 80 1c     movt    r12, #384
+// CHECK2-NEXT:  280000c:       fc 44   add     r12, pc
+// CHECK2-NEXT:  280000e:       60 47   bx      r12
 // CHECK2: __ThumbV7PILongThunk_preemptible:
-// CHECK2-NEXT:  1000010:       40 f2 24 0c     movw    r12, #36
-// CHECK2-NEXT:  1000014:       c0 f2 80 0c     movt    r12, #128
-// CHECK2-NEXT:  1000018:       fc 44   add     r12, pc
-// CHECK2-NEXT:  100001a:       60 47   bx      r12
+// CHECK2-NEXT:  2800010:       40 f2 24 0c     movw    r12, #36
+// CHECK2-NEXT:  2800014:       c0 f2 80 1c     movt    r12, #384
+// CHECK2-NEXT:  2800018:       fc 44   add     r12, pc
+// CHECK2-NEXT:  280001a:       60 47   bx      r12
 // CHECK2: __ThumbV7PILongThunk_far_preemptible:
-// CHECK2-NEXT:  100001c:       40 f2 28 0c     movw    r12, #40
-// CHECK2-NEXT:  1000020:       c0 f2 80 0c     movt    r12, #128
-// CHECK2-NEXT:  1000024:       fc 44   add     r12, pc
-// CHECK2-NEXT:  1000026:       60 47   bx      r12
+// CHECK2-NEXT:  280001c:       40 f2 28 0c     movw    r12, #40
+// CHECK2-NEXT:  2800020:       c0 f2 80 1c     movt    r12, #384
+// CHECK2-NEXT:  2800024:       fc 44   add     r12, pc
+// CHECK2-NEXT:  2800026:       60 47   bx      r12
+// CHECK2: __ThumbV7PILongThunk_far_nonpreemptible:
+// CHECK2-NEXT:  2800028:       4f f6 cd 7c     movw    r12, #65485
+// CHECK2-NEXT:  280002c:       c0 f2 7f 1c     movt    r12, #383
+// CHECK2-NEXT:  2800030:       fc 44   add     r12, pc
+// CHECK2-NEXT:  2800032:       60 47   bx      r12
 
  .section .text.3, "ax", %progbits
-.balign 0x0800000
+.balign 0x2000000
 far_preemptible:
+far_nonpreemptible:
  bl elsewhere
+
+ .section .text.4, "ax", %progbits
+.balign 0x2000000
+far_nonpreemptible_alias:
+ bl elsewhere
+
 // CHECK3: far_preemptible:
-// CHECK3:  1800000:       00 f0 16 e8     blx     #44
+// CHECK3:  4000000:       00 f0 16 e8     blx     #44
 
 // CHECK4: Disassembly of section .plt:
 // CHECK4-NEXT: $a:
-// CHECK4-NEXT:  1800010:      04 e0 2d e5     str     lr, [sp, #-4]!
-// CHECK4-NEXT:  1800014:      00 e6 8f e2     add     lr, pc, #0, #12
-// CHECK4-NEXT:  1800018:      00 ea 8e e2     add     lr, lr, #0, #20
-// CHECK4-NEXT:  180001c:      ec ff be e5     ldr     pc, [lr, #4076]!
+// CHECK4-NEXT:  4000010:      04 e0 2d e5     str     lr, [sp, #-4]!
+// CHECK4-NEXT:  4000014:      00 e6 8f e2     add     lr, pc, #0, #12
+// CHECK4-NEXT:  4000018:      00 ea 8e e2     add     lr, lr, #0, #20
+// CHECK4-NEXT:  400001c:      ec ff be e5     ldr     pc, [lr, #4076]!
 // CHECK4: $d:
-// CHECK4-NEXT:  1800020:      d4 d4 d4 d4     .word   0xd4d4d4d4
-// CHECK4-NEXT:  1800024:      d4 d4 d4 d4     .word   0xd4d4d4d4
-// CHECK4-NEXT:  1800028:      d4 d4 d4 d4     .word   0xd4d4d4d4
-// CHECK4-NEXT:  180002c:      d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK4-NEXT:  4000020:      d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK4-NEXT:  4000024:      d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK4-NEXT:  4000028:      d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK4-NEXT:  400002c:      d4 d4 d4 d4     .word   0xd4d4d4d4
 // CHECK4: $a:
-// CHECK4-NEXT:  1800030:      00 c6 8f e2     add     r12, pc, #0, #12
-// CHECK4-NEXT:  1800034:      00 ca 8c e2     add     r12, r12, #0, #20
-// CHECK4-NEXT:  1800038:      d4 ff bc e5     ldr     pc, [r12, #4052]!
+// CHECK4-NEXT:  4000030:      00 c6 8f e2     add     r12, pc, #0, #12
+// CHECK4-NEXT:  4000034:      00 ca 8c e2     add     r12, r12, #0, #20
+// CHECK4-NEXT:  4000038:      d4 ff bc e5     ldr     pc, [r12, #4052]!
 // CHECK4: $d:
-// CHECK4-NEXT:  180003c:      d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK4-NEXT:  400003c:      d4 d4 d4 d4     .word   0xd4d4d4d4
 // CHECK4: $a:
-// CHECK4-NEXT:  1800040:      00 c6 8f e2     add     r12, pc, #0, #12
-// CHECK4-NEXT:  1800044:      00 ca 8c e2     add     r12, r12, #0, #20
-// CHECK4-NEXT:  1800048:      c8 ff bc e5     ldr     pc, [r12, #4040]!
+// CHECK4-NEXT:  4000040:      00 c6 8f e2     add     r12, pc, #0, #12
+// CHECK4-NEXT:  4000044:      00 ca 8c e2     add     r12, r12, #0, #20
+// CHECK4-NEXT:  4000048:      c8 ff bc e5     ldr     pc, [r12, #4040]!
 // CHECK4: $d:
-// CHECK4-NEXT:  180004c:      d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK4-NEXT:  400004c:      d4 d4 d4 d4     .word   0xd4d4d4d4
 // CHECK4: $a:
-// CHECK4-NEXT:  1800050:      00 c6 8f e2     add     r12, pc, #0, #12
-// CHECK4-NEXT:  1800054:      00 ca 8c e2     add     r12, r12, #0, #20
-// CHECK4-NEXT:  1800058:      bc ff bc e5     ldr     pc, [r12, #4028]!
+// CHECK4-NEXT:  4000050:      00 c6 8f e2     add     r12, pc, #0, #12
+// CHECK4-NEXT:  4000054:      00 ca 8c e2     add     r12, r12, #0, #20
+// CHECK4-NEXT:  4000058:      bc ff bc e5     ldr     pc, [r12, #4028]!
 // CHECK4: $d:
-// CHECK4-NEXT:  180005c:      d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK4-NEXT:  400005c:      d4 d4 d4 d4     .word   0xd4d4d4d4