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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310756 91177308-0d34-0410-b5e6-96231b3b80d8

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())

test/CodeGen/X86/weak-undef.ll

@@ -0,0 +1,58 @@
+; RUN: llc < %s -relocation-model=pic -mtriple=x86_64-pc-linux | FileCheck %s
+; RUN: llc < %s -relocation-model=pic -mtriple=i386-pc-linux | FileCheck --check-prefix=I386 %s
+
+@foo1 = extern_weak hidden global i32, align 4
+define i32* @bar1() {
+  ret i32* @foo1
+}
+; CHECK: bar1:
+; CHECK: movq foo1@GOTPCREL(%rip), %rax
+; I386: bar1:
+; I386: leal foo1@GOTOFF(%eax), %eax
+
+@foo2 = external hidden global i32, align 4
+define i32* @bar2() {
+  ret i32* @foo2
+}
+; CHECK: bar2:
+; CHECK: leaq foo2(%rip), %rax
+; I386: bar2:
+; I386: leal foo2@GOTOFF(%eax), %eax
+
+declare extern_weak hidden void @foo3()
+define void @bar3() {
+  call void @foo3()
+  ret void
+}
+; CHECK: bar3:
+; CHECK: callq foo3
+; I386: bar3:
+; I386: calll foo3
+
+declare external hidden void @foo4()
+define void @bar4() {
+  call void @foo4()
+  ret void
+}
+; CHECK: bar4:
+; CHECK: callq foo4
+; I386: bar4:
+; I386: calll foo4
+
+declare extern_weak hidden i32 @foo5()
+define i32()* @bar5() {
+  ret i32()* @foo5
+}
+; CHECK: bar5:
+; CHECK: movq foo5@GOTPCREL(%rip), %rax
+; I386: bar5:
+; I386: leal foo5@GOTOFF(%eax), %eax
+
+declare external hidden i32 @foo6()
+define i32()* @bar6() {
+  ret i32()* @foo6
+}
+; CHECK: bar6:
+; CHECK: leaq foo6(%rip), %rax
+; I386: bar6:
+; I386: leal foo6@GOTOFF(%eax), %eax