[IR] AutoUpgrade ModuleFlagBehavior for PIC and PIE level

Summary:
From r303590, ModuleFlagBehavior for PIC and PIE level is changed from
Error to Max. This will cause bitcode compatibility issue when linking
against a bitcode static archive built with old compiler.
Add an auto-ugprade path to upgrade the the ModuleFlagBehavior in the
old bitcode to match the new one so IRLinker can link them.

Reviewers: tejohnson, mehdi_amini, dexonsmith

Reviewed By: dexonsmith

Subscribers: hans, llvm-commits

Differential Revision: https://reviews.llvm.org/D36556

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311387 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/AutoUpgrade.cpp

@@ -2284,14 +2284,14 @@ bool llvm::UpgradeDebugInfo(Module &M) {
 }
 
 bool llvm::UpgradeModuleFlags(Module &M) {
-  const NamedMDNode *ModFlags = M.getModuleFlagsMetadata();
+  NamedMDNode *ModFlags = M.getModuleFlagsMetadata();
   if (!ModFlags)
     return false;
 
-  bool HasObjCFlag = false, HasClassProperties = false;
+  bool HasObjCFlag = false, HasClassProperties = false, Changed = false;
   for (unsigned I = 0, E = ModFlags->getNumOperands(); I != E; ++I) {
     MDNode *Op = ModFlags->getOperand(I);
-    if (Op->getNumOperands() < 2)
+    if (Op->getNumOperands() != 3)
       continue;
     MDString *ID = dyn_cast_or_null<MDString>(Op->getOperand(1));
     if (!ID)
@@ -2300,7 +2300,24 @@ bool llvm::UpgradeModuleFlags(Module &M) {
       HasObjCFlag = true;
     if (ID->getString() == "Objective-C Class Properties")
       HasClassProperties = true;
+    // Upgrade PIC/PIE Module Flags. The module flag behavior for these two
+    // field was Error and now they are Max.
+    if (ID->getString() == "PIC Level" || ID->getString() == "PIE Level") {
+      if (auto *Behavior =
+              mdconst::dyn_extract_or_null<ConstantInt>(Op->getOperand(0))) {
+        if (Behavior->getLimitedValue() == Module::Error) {
+          Type *Int32Ty = Type::getInt32Ty(M.getContext());
+          Metadata *Ops[3] = {
+              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;
+        }
+      }
+    }
   }
+
   // "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
@@ -2309,9 +2326,10 @@ bool llvm::UpgradeModuleFlags(Module &M) {
   if (HasObjCFlag && !HasClassProperties) {
     M.addModuleFlag(llvm::Module::Override, "Objective-C Class Properties",
                     (uint32_t)0);
-    return true;
+    Changed = true;
   }
-  return false;
+
+  return Changed;
 }
 
 static bool isOldLoopArgument(Metadata *MD) {

test/Bitcode/upgrade-module-flag.ll

@@ -1,9 +1,13 @@
 ; RUN: llvm-as < %s | llvm-dis | FileCheck %s
 ; RUN: verify-uselistorder < %s
 
-!llvm.module.flags = !{!0}
+!llvm.module.flags = !{!0, !1, !2}
 
-!0 = !{i32 1, !"Objective-C Image Info Version", i32 0}
+!0 = !{i32 1, !"PIC Level", i32 1}
+!1 = !{i32 1, !"PIE Level", i32 1}
+!2 = !{i32 1, !"Objective-C Image Info Version", i32 0}
 
-; CHECK: !0 = !{i32 1, !"Objective-C Image Info Version", i32 0}
+; CHECK: !0 = !{i32 7, !"PIC Level", i32 1}
-; CHECK: !1 = !{i32 4, !"Objective-C Class Properties", i32 0}
+; 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}

test/Linker/module-flags-pic-1-a.ll

@@ -2,8 +2,8 @@
 
 ; test linking modules with specified and default PIC levels
 
-!0 = !{ i32 1, !"PIC Level", i32 1 }
+!0 = !{ i32 7, !"PIC Level", i32 1 }
 
 !llvm.module.flags = !{!0}
 ; CHECK: !llvm.module.flags = !{!0}
-; CHECK: !0 = !{i32 1, !"PIC Level", i32 1}
+; CHECK: !0 = !{i32 7, !"PIC Level", i32 1}