Fix access to undefined weak symbols in pic code

When the access to a weak symbol is not a call, the access has to be
able to produce the value 0 at runtime.

We were sometimes producing code sequences where that was not possible
if the code was leaded more than 4g away from 0.

llvm-svn: 310756

1 files changed, 17 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86Subtarget.cpp b/llvm/lib/Target/X86/X86Subtarget.cpp
index 493084f795f..1b02b88c187 100644
--- a/llvm/lib/Target/X86/X86Subtarget.cpp
+++ b/llvm/lib/Target/X86/X86Subtarget.cpp
@@ -99,6 +99,22 @@ X86Subtarget::classifyLocalReference(const GlobalValue *GV) const {
   return X86II::MO_GOTOFF;
 }
 
+static bool shouldAssumeGlobalReferenceLocal(const X86Subtarget *ST,
+                                             const TargetMachine &TM,
+                                             const Module &M,
+                                             const GlobalValue *GV) {
+  if (!TM.shouldAssumeDSOLocal(M, GV))
+    return false;
+  // A weak reference can end up being 0. If the code can be more that 4g away
+  // from zero and we are using the small code model we have to treat it as non
+  // local.
+  if (GV && GV->hasExternalWeakLinkage() &&
+      TM.getCodeModel() == CodeModel::Small && TM.isPositionIndependent() &&
+      ST->is64Bit() && ST->isTargetELF())
+    return false;
+  return true;
+}
+
 unsigned char X86Subtarget::classifyGlobalReference(const GlobalValue *GV,
                                                     const Module &M) const {
   // Large model never uses stubs.
@@ -118,7 +134,7 @@ unsigned char X86Subtarget::classifyGlobalReference(const GlobalValue *GV,
     }
   }
 
-  if (TM.shouldAssumeDSOLocal(M, GV))
+  if (shouldAssumeGlobalReferenceLocal(this, TM, M, GV))
     return classifyLocalReference(GV);
 
   if (isTargetCOFF())