[PATCH] D36497: compute isPreemtible only once

[Rafael Ávila de Espíndola via Phabricator via llvm-commits]

rafael created this revision.
Herald added a subscriber: emaste.

This is probably a small optimization, but the main motivation is having a way of fixing pr34053 that doesn't require a hash lookup in isPreempitible.


https://reviews.llvm.org/D36497

Files:
  ELF/Relocations.cpp
  ELF/Symbols.cpp
  ELF/Symbols.h
  ELF/Writer.cpp


Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -1182,6 +1182,9 @@
   applySynthetic({In<ELFT>::EhFrame},
                  [](SyntheticSection *SS) { SS->finalizeContents(); });
 
+  for (Symbol *S : Symtab->getSymbols())
+    S->body()->IsPreemptible = S->body()->computeIsPreemptible();
+
   // Scan relocations. This must be done after every symbol is declared so that
   // we can correctly decide if a dynamic relocation is needed.
   forEachRelSec(scanRelocations<ELFT>);
Index: ELF/Symbols.h
===================================================================
--- ELF/Symbols.h
+++ ELF/Symbols.h
@@ -70,7 +70,8 @@
   }
   bool isLocal() const { return IsLocal; }
   InputFile *getFile() const;
-  bool isPreemptible() const;
+  bool isPreemptible() const { return IsPreemptible; }
+  bool computeIsPreemptible() const;
   StringRef getName() const { return Name; }
   uint8_t getVisibility() const { return StOther & 0x3; }
   void parseSymbolVersion();
@@ -121,6 +122,8 @@
   // True if this symbol is in the Igot sub-section of the .got.plt or .got.
   unsigned IsInIgot : 1;
 
+  unsigned IsPreemptible : 1;
+
   // The following fields have the same meaning as the ELF symbol attributes.
   uint8_t Type;    // symbol type
   uint8_t StOther; // st_other field value
Index: ELF/Symbols.cpp
===================================================================
--- ELF/Symbols.cpp
+++ ELF/Symbols.cpp
@@ -127,7 +127,8 @@
                        uint8_t Type)
     : SymbolKind(K), NeedsPltAddr(false), IsLocal(IsLocal),
       IsInGlobalMipsGot(false), Is32BitMipsGot(false), IsInIplt(false),
-      IsInIgot(false), Type(Type), StOther(StOther), Name(Name) {}
+      IsInIgot(false), IsPreemptible(false), Type(Type), StOther(StOther),
+      Name(Name) {}
 
 InputFile *SymbolBody::getFile() const {
   if (isLocal())
@@ -137,10 +138,8 @@
 
 // Returns true if a symbol can be replaced at load-time by a symbol
 // with the same name defined in other ELF executable or DSO.
-bool SymbolBody::isPreemptible() const {
-  if (isLocal())
-    return false;
-
+bool SymbolBody::computeIsPreemptible() const {
+  assert(!isLocal());
   // Shared symbols resolve to the definition in the DSO. The exceptions are
   // symbols with copy relocations (which resolve to .bss) or preempt plt
   // entries (which resolve to that plt entry).
Index: ELF/Relocations.cpp
===================================================================
--- ELF/Relocations.cpp
+++ ELF/Relocations.cpp
@@ -149,7 +149,7 @@
                                        InputSectionBase &C, uint64_t Offset,
                                        int64_t Addend, RelExpr Expr) {
   // The Dynamic TLS Module Index Relocation for a symbol defined in an
-  // executable is always 1. If the target Symbol is not preemtible then
+  // executable is always 1. If the target Symbol is not preemptible then
   // we know the offset into the TLS block at static link time.
   bool NeedDynId = Body.isPreemptible() || Config->Shared;
   bool NeedDynOff = Body.isPreemptible();
@@ -527,6 +527,7 @@
   // interpose any aliases.
   for (SharedSymbol *Sym : getSymbolsAt<ELFT>(SS)) {
     Sym->CopyRelSec = Sec;
+    Sym->IsPreemptible = false;
     Sym->CopyRelSecOff = Off;
     Sym->symbol()->IsUsedInRegularObj = true;
   }
@@ -612,6 +613,7 @@
     // plt. That is identified by special relocation types (R_X86_64_JUMP_SLOT,
     // R_386_JMP_SLOT, etc).
     Body.NeedsPltAddr = true;
+    Body.IsPreemptible = false;
     return toPlt(Expr);
   }
 


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