[PATCH] D36604: PR34148: Do not assume we can use a copy relocation for an `external_weak` global

[Richard Smith - zygoloid via Phabricator via llvm-commits]

rsmith created this revision.
Herald added a subscriber: sanjoy.

An `external_weak` global may be intended to resolve as a null pointer if it's not defined, so it doesn't make sense to use a copy relocation for it.

See also https://reviews.llvm.org/D36280 (which fixes an overlapping issue for X86).


Repository:
  rL LLVM

https://reviews.llvm.org/D36604

Files:
  lib/Target/TargetMachine.cpp
  test/CodeGen/X86/global-access-pie-copyrelocs.ll


Index: test/CodeGen/X86/global-access-pie-copyrelocs.ll
===================================================================
--- test/CodeGen/X86/global-access-pie-copyrelocs.ll
+++ test/CodeGen/X86/global-access-pie-copyrelocs.ll
@@ -63,6 +63,20 @@
   ret i32 %0
 }
 
+; ExternalWeak Linkage
+ at e = extern_weak global i32, align 4
+
+define i32* @my_access_global_d() #0 {
+; X32-LABEL: my_access_global_d:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32:       movl e at GOT(%eax), %eax
+; X64-LABEL: my_access_global_d:
+; X64:       movq e at GOTPCREL(%rip), %rax
+
+entry:
+  ret i32* @e
+}
+
 ; External Linkage, only declaration, store a value.
 
 define i32 @my_access_global_store_d() #0 {
Index: lib/Target/TargetMachine.cpp
===================================================================
--- lib/Target/TargetMachine.cpp
+++ lib/Target/TargetMachine.cpp
@@ -154,8 +154,9 @@
       return true;
 
     bool IsTLS = GV && GV->isThreadLocal();
-    bool IsAccessViaCopyRelocs =
-        Options.MCOptions.MCPIECopyRelocations && GV && isa<GlobalVariable>(GV);
+    bool IsAccessViaCopyRelocs = Options.MCOptions.MCPIECopyRelocations && GV &&
+                                 isa<GlobalVariable>(GV) &&
+                                 !GV->hasExternalWeakLinkage();
     Triple::ArchType Arch = TT.getArch();
     bool IsPPC =
         Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;


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