[AutoUpgrade] Fix a compatibility issue with module flag

[steven_wu]

Summary

After r304661, module flag to record objective-c image info section is
encoded without whitespaces after comma. The new name is equivalent to
the old one, except that when LTO a module built by old compiler and a
module built by a new compiler, it will fail with conflicting values.

Fix the issue by removing whitespaces in bitcode upgrade path.

rdar://problem/34416934

[compnerd]

Oh, sorry about that! Thanks for fixing this.

[hans]

Was I CC'd on this because it's a candidate for 5.0.1? If so, +Tom who manages that release.

[steven_wu]

Thanks Hans. Yes, it will be good to pick this up for 5.0.1

llvm/trunk/lib/IR/AutoUpgrade.cpp

if (ID->getString() == "PIC Level" || ID->getString() == "PIE Level") {
               ConstantAsMetadata::get(ConstantInt::get(Int32Ty, Module::Max)),
               MDString::get(M.getContext(), ID->getString()),
               Op->getOperand(2)};
           ModFlags->setOperand(I, MDNode::get(M.getContext(), Ops));
           Changed = true;
         }
       }
     }
+    // Upgrade Objective-C Image Info Section. Removed the whitespce in the
+    // section name so that llvm-lto will not complain about mismatching
+    // module flags that is functionally the same.
+    if (ID->getString() == "Objective-C Image Info Section") {
+      if (auto *Value = dyn_cast_or_null<MDString>(Op->getOperand(2))) {
+        SmallVector<StringRef, 4> ValueComp;
+        Value->getString().split(ValueComp, " ");
+        if (ValueComp.size() != 1) {
+          std::string NewValue;
+          for (auto &S : ValueComp)
+            NewValue += S.str();
+          Metadata *Ops[3] = {Op->getOperand(0), Op->getOperand(1),
+                              MDString::get(M.getContext(), NewValue)};
+          ModFlags->setOperand(I, MDNode::get(M.getContext(), Ops));
+          Changed = true;
+        }
+      }
+    }
   }
 
   // "Objective-C Class Properties" is recently added for Objective-C. We
   // upgrade ObjC bitcodes to contain a "Objective-C Class Properties" module
   // flag of value 0, so we can correclty downgrade this flag when trying to
   // link an ObjC bitcode without this module flag with an ObjC bitcode with
   // this module flag.
   if (HasObjCFlag && !HasClassProperties) {

llvm/trunk/test/Bitcode/upgrade-module-flag.ll

 ; RUN: llvm-as < %s | llvm-dis | FileCheck %s
 ; RUN: verify-uselistorder < %s
 
-!llvm.module.flags = !{!0, !1, !2}
+!llvm.module.flags = !{!0, !1, !2, !3}
 
 !0 = !{i32 1, !"PIC Level", i32 1}
 !1 = !{i32 1, !"PIE Level", i32 1}
 !2 = !{i32 1, !"Objective-C Image Info Version", i32 0}
+!3 = !{i32 1, !"Objective-C Image Info Section", !"__DATA, __objc_imageinfo, regular, no_dead_strip"}
 
 ; CHECK: !0 = !{i32 7, !"PIC Level", i32 1}
 ; CHECK: !1 = !{i32 7, !"PIE Level", i32 1}
 ; CHECK: !2 = !{i32 1, !"Objective-C Image Info Version", i32 0}
-; CHECK: !3 = !{i32 4, !"Objective-C Class Properties", i32 0}
+; CHECK: !3 = !{i32 1, !"Objective-C Image Info Section", !"__DATA,__objc_imageinfo,regular,no_dead_strip"}
+; CHECK: !4 = !{i32 4, !"Objective-C Class Properties", i32 0}