New llc option pie-copy-relocations to optimize access to extern globals.

This option indicates copy relocations support is available from the linker
when building as PIE and allows accesses to extern globals to avoid the GOT.

Differential Revision: https://reviews.llvm.org/D24849

llvm-svn: 284160

1 files changed, 3 insertions, 4 deletions

diff --git a/llvm/lib/Target/TargetMachine.cpp b/llvm/lib/Target/TargetMachine.cpp
index 43a587ba847..792280af84d 100644
--- a/llvm/lib/Target/TargetMachine.cpp
+++ b/llvm/lib/Target/TargetMachine.cpp
@@ -115,9 +115,6 @@ static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
   llvm_unreachable("invalid TLS model");
 }
 
-// FIXME: make this a proper option
-static bool CanUseCopyRelocWithPIE = false;
-
 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
                                          const GlobalValue *GV) const {
   Reloc::Model RM = getRelocationModel();
@@ -154,8 +151,10 @@ bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
       return true;
 
     bool IsTLS = GV && GV->isThreadLocal();
+    bool IsAccessViaCopyRelocs =
+        Options.MCOptions.MCPIECopyRelocations && GV && isa<GlobalVariable>(GV);
     // Check if we can use copy relocations.
-    if (!IsTLS && (RM == Reloc::Static || CanUseCopyRelocWithPIE))
+    if (!IsTLS && (RM == Reloc::Static || IsAccessViaCopyRelocs))
       return true;
   }