[lld] r241294 - COFF: Make symbols satisfy weak ordering.
Rui Ueyama
ruiu at google.com
Thu Jul 2 13:33:48 PDT 2015
Author: ruiu
Date: Thu Jul 2 15:33:48 2015
New Revision: 241294
URL: http://llvm.org/viewvc/llvm-project?rev=241294&view=rev
Log:
COFF: Make symbols satisfy weak ordering.
Previously, SymbolBody::compare(A, B) didn't satisfy weak ordering.
There was a case that A < B and B < A could have been true.
This is because we just pick LHS if A and B are consisdered equivalent.
This patch is to make symbols being weakly ordered. If A and B are
not tie, one of A < B && B > A or A > B && B < A is true.
This is not an improtant property for a single-threaded environment
because everything is deterministic anyways. However, in a multi-
threaded environment, this property becomes important.
If a symbol is defined or lazy, ties are resolved by its file index.
For simple types that we don't really care about their identities,
symbols are compared by their addresses.
Modified:
lld/trunk/COFF/InputFiles.cpp
lld/trunk/COFF/InputFiles.h
lld/trunk/COFF/Symbols.cpp
lld/trunk/COFF/Symbols.h
Modified: lld/trunk/COFF/InputFiles.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/InputFiles.cpp?rev=241294&r1=241293&r2=241294&view=diff
==============================================================================
--- lld/trunk/COFF/InputFiles.cpp (original)
+++ lld/trunk/COFF/InputFiles.cpp Thu Jul 2 15:33:48 2015
@@ -32,6 +32,8 @@ using llvm::sys::fs::file_magic;
namespace lld {
namespace coff {
+int InputFile::NextIndex = 0;
+
// Returns the last element of a path, which is supposed to be a filename.
static StringRef getBasename(StringRef Path) {
size_t Pos = Path.find_last_of("\\/");
Modified: lld/trunk/COFF/InputFiles.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/InputFiles.h?rev=241294&r1=241293&r2=241294&view=diff
==============================================================================
--- lld/trunk/COFF/InputFiles.h (original)
+++ lld/trunk/COFF/InputFiles.h Thu Jul 2 15:33:48 2015
@@ -62,8 +62,15 @@ public:
// Returns .drectve section contents if exist.
StringRef getDirectives() { return StringRef(Directives).trim(); }
+ // Each file has a unique index. The index number is used to
+ // resolve ties in symbol resolution.
+ int Index;
+ static int NextIndex;
+
protected:
- InputFile(Kind K, MemoryBufferRef M) : MB(M), FileKind(K) {}
+ InputFile(Kind K, MemoryBufferRef M)
+ : Index(NextIndex++), MB(M), FileKind(K) {}
+
MemoryBufferRef MB;
std::string Directives;
Modified: lld/trunk/COFF/Symbols.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Symbols.cpp?rev=241294&r1=241293&r2=241294&view=diff
==============================================================================
--- lld/trunk/COFF/Symbols.cpp (original)
+++ lld/trunk/COFF/Symbols.cpp Thu Jul 2 15:33:48 2015
@@ -47,7 +47,6 @@ int SymbolBody::compare(SymbolBody *Othe
// First handle comparisons between two different kinds.
if (LK != RK) {
-
if (RK > LastDefinedKind) {
if (LK == LazyKind && cast<Undefined>(Other)->WeakAlias)
return -1;
@@ -94,12 +93,16 @@ int SymbolBody::compare(SymbolBody *Othe
case DefinedRegularKind: {
auto *LHS = cast<DefinedRegular>(this);
auto *RHS = cast<DefinedRegular>(Other);
- return (LHS->isCOMDAT() && RHS->isCOMDAT()) ? 1 : 0;
+ if (LHS->isCOMDAT() && RHS->isCOMDAT())
+ return LHS->getFileIndex() < RHS->getFileIndex() ? 1 : -1;
+ return 0;
}
case DefinedCommonKind: {
auto *LHS = cast<DefinedCommon>(this);
auto *RHS = cast<DefinedCommon>(Other);
+ if (LHS->getSize() == RHS->getSize())
+ return LHS->getFileIndex() < RHS->getFileIndex() ? 1 : -1;
return LHS->getSize() > RHS->getSize() ? 1 : -1;
}
@@ -111,17 +114,30 @@ int SymbolBody::compare(SymbolBody *Othe
return 0;
// Non-replaceable symbols win, but even two replaceable symboles don't
- // tie.
+ // tie. If both symbols are replaceable, choice is arbitrary.
+ if (RHS->IsReplaceable && LHS->IsReplaceable)
+ return uintptr_t(LHS) < uintptr_t(RHS) ? 1 : -1;
return LHS->IsReplaceable ? -1 : 1;
}
- case LazyKind:
- // Don't tie, just pick the LHS.
- return 1;
-
- case UndefinedKind:
- // Don't tie, just pick the LHS unless the RHS has a weak alias.
- return cast<Undefined>(Other)->WeakAlias ? -1 : 1;
+ case LazyKind: {
+ // Don't tie, pick the earliest.
+ auto *LHS = cast<Lazy>(this);
+ auto *RHS = cast<Lazy>(Other);
+ return LHS->getFileIndex() < RHS->getFileIndex() ? 1 : -1;
+ }
+
+ case UndefinedKind: {
+ auto *LHS = cast<Undefined>(this);
+ auto *RHS = cast<Undefined>(Other);
+ // Tie if both undefined symbols have different weak aliases.
+ if (LHS->WeakAlias && RHS->WeakAlias) {
+ if (LHS->WeakAlias->repl() != RHS->WeakAlias->repl())
+ return 0;
+ return uintptr_t(LHS) < uintptr_t(RHS) ? 1 : -1;
+ }
+ return LHS->WeakAlias ? 1 : -1;
+ }
case DefinedLocalImportKind:
case DefinedImportThunkKind:
Modified: lld/trunk/COFF/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Symbols.h?rev=241294&r1=241293&r2=241294&view=diff
==============================================================================
--- lld/trunk/COFF/Symbols.h (original)
+++ lld/trunk/COFF/Symbols.h Thu Jul 2 15:33:48 2015
@@ -139,6 +139,8 @@ public:
return S->kind() <= LastDefinedCOFFKind;
}
+ int getFileIndex() { return File->Index; }
+
protected:
ObjectFile *File;
const coff_symbol_generic *Sym;
@@ -231,6 +233,8 @@ public:
// was already returned.
ErrorOr<std::unique_ptr<InputFile>> getMember();
+ int getFileIndex() { return File->Index; }
+
private:
ArchiveFile *File;
const Archive::Symbol Sym;
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