Cache result when tail merging too.

This speeds up a link of chromium with -O2 (but no icf,gc) from
1.940664632 to 1.925578119.

llvm-svn: 268639

2 files changed, 7 insertions, 7 deletions

diff --git a/lld/ELF/InputSection.cpp b/lld/ELF/InputSection.cpp
index 41703fb73b3..e5fa4089cc0 100644
--- a/lld/ELF/InputSection.cpp
+++ b/lld/ELF/InputSection.cpp
@@ -479,14 +479,15 @@ typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) {
   // Compute the Addend and if the Base is cached, return.
   uintX_t Addend = Offset - Start;
   uintX_t &Base = I->second;
-  auto *MOS = static_cast<MergeOutputSection<ELFT> *>(this->OutSec);
-  if (!MOS->shouldTailMerge())
+  assert(Base != MergeInputSection<ELFT>::PieceDead);
+  if (Base != MergeInputSection<ELFT>::PieceLive)
     return Base + Addend;
 
   // Map the base to the offset in the output section and cache it.
   ArrayRef<uint8_t> D = this->getSectionData();
   StringRef Data((const char *)D.data(), D.size());
   StringRef Entry = Data.substr(Start, End - Start);
+  auto *MOS = static_cast<MergeOutputSection<ELFT> *>(this->OutSec);
   Base = MOS->getOffset(Entry);
   return Base + Addend;
 }
diff --git a/lld/ELF/InputSection.h b/lld/ELF/InputSection.h
index ea8fd438cdf..17313d204d3 100644
--- a/lld/ELF/InputSection.h
+++ b/lld/ELF/InputSection.h
@@ -152,12 +152,11 @@ public:
   enum {
     // The piece is dead.
     PieceDead = uintX_t(-1),
-    // The piece is live, and an offset has not yet been assigned. After offsets
+    // The piece is live, but an offset has not yet been assigned. After offsets
     // have been assigned, if the output section uses tail merging, the field
-    // will still have this value and the output section offset is available
-    // from MergeOutputSection<ELFT>::getOffset(). Otherwise, this value has no
-    // special significance, it just means that the offset is 0.
-    PieceLive = uintX_t(0),
+    // will still have this value and the output section offset is computed
+    // lazilly.
+    PieceLive = uintX_t(-2),
   };
 
   std::pair<std::pair<uintX_t, uintX_t> *, uintX_t>