7 files changed, 43 insertions, 14 deletions
diff --git a/llvm/include/llvm/IR/Module.h b/llvm/include/llvm/IR/Module.h
index 3024d9e27a2..5e1f680c5b3 100644
--- a/llvm/include/llvm/IR/Module.h
+++ b/llvm/include/llvm/IR/Module.h
@@ -139,9 +139,12 @@ public:
     /// during the append operation.
     AppendUnique = 6,
 
+    /// Takes the max of the two values, which are required to be integers.
+    Max = 7,
+
     // Markers:
     ModFlagBehaviorFirstVal = Error,
-    ModFlagBehaviorLastVal = AppendUnique
+    ModFlagBehaviorLastVal = Max
   };
 
   /// Checks if Metadata represents a valid ModFlagBehavior, and stores the
diff --git a/llvm/lib/IR/Module.cpp b/llvm/lib/IR/Module.cpp
index 12c258d95f5..95673e515a5 100644
--- a/llvm/lib/IR/Module.cpp
+++ b/llvm/lib/IR/Module.cpp
@@ -481,7 +481,7 @@ PICLevel::Level Module::getPICLevel() const {
 }
 
 void Module::setPICLevel(PICLevel::Level PL) {
-  addModuleFlag(ModFlagBehavior::Error, "PIC Level", PL);
+  addModuleFlag(ModFlagBehavior::Max, "PIC Level", PL);
 }
 
 PIELevel::Level Module::getPIELevel() const {
@@ -495,7 +495,7 @@ PIELevel::Level Module::getPIELevel() const {
 }
 
 void Module::setPIELevel(PIELevel::Level PL) {
-  addModuleFlag(ModFlagBehavior::Error, "PIE Level", PL);
+  addModuleFlag(ModFlagBehavior::Max, "PIE Level", PL);
 }
 
 void Module::setProfileSummary(Metadata *M) {
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 21e8048442b..ffb9ad27922 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -1282,6 +1282,13 @@ Verifier::visitModuleFlag(const MDNode *Op,
     // These behavior types accept any value.
     break;
 
+  case Module::Max: {
+    Assert(mdconst::dyn_extract_or_null<ConstantInt>(Op->getOperand(2)),
+           "invalid value for 'max' module flag (expected constant integer)",
+           Op->getOperand(2));
+    break;
+  }
+
   case Module::Require: {
     // The value should itself be an MDNode with two operands, a flag ID (an
     // MDString), and a value.
diff --git a/llvm/lib/Linker/IRMover.cpp b/llvm/lib/Linker/IRMover.cpp
index c0af21aa148..defad190498 100644
--- a/llvm/lib/Linker/IRMover.cpp
+++ b/llvm/lib/Linker/IRMover.cpp
@@ -1157,6 +1157,11 @@ Error IRLinker::linkModuleFlagsMetadata() {
         mdconst::extract<ConstantInt>(DstOp->getOperand(0));
     unsigned DstBehaviorValue = DstBehavior->getZExtValue();
 
+    auto overrideDstValue = [&]() {
+      DstModFlags->setOperand(DstIndex, SrcOp);
+      Flags[ID].first = SrcOp;
+    };
+
     // If either flag has override behavior, handle it first.
     if (DstBehaviorValue == Module::Override) {
       // Diagnose inconsistent flags which both have override behavior.
@@ -1167,8 +1172,7 @@ Error IRLinker::linkModuleFlagsMetadata() {
       continue;
     } else if (SrcBehaviorValue == Module::Override) {
       // Update the destination flag to that of the source.
-      DstModFlags->setOperand(DstIndex, SrcOp);
-      Flags[ID].first = SrcOp;
+      overrideDstValue();
       continue;
     }
 
@@ -1204,6 +1208,15 @@ Error IRLinker::linkModuleFlagsMetadata() {
       }
       continue;
     }
+    case Module::Max: {
+      ConstantInt *DstValue =
+          mdconst::extract<ConstantInt>(DstOp->getOperand(2));
+      ConstantInt *SrcValue =
+          mdconst::extract<ConstantInt>(SrcOp->getOperand(2));
+      if (SrcValue->getZExtValue() > DstValue->getZExtValue())
+        overrideDstValue();
+      break;
+    }
     case Module::Append: {
       MDNode *DstValue = cast<MDNode>(DstOp->getOperand(2));
       MDNode *SrcValue = cast<MDNode>(SrcOp->getOperand(2));
diff --git a/llvm/test/Linker/Inputs/module-flags-pic-2-b.ll b/llvm/test/Linker/Inputs/module-flags-pic-2-b.ll
index 0d78cafc6a0..f652eddb384 100644
--- a/llvm/test/Linker/Inputs/module-flags-pic-2-b.ll
+++ b/llvm/test/Linker/Inputs/module-flags-pic-2-b.ll
@@ -1,3 +1,4 @@
-!0 = !{ i32 1, !"PIC Level", i32 2 }
+!0 = !{ i32 7, !"PIC Level", i32 2 }
+!1 = !{ i32 7, !"PIE Level", i32 2 }
 
-!llvm.module.flags = !{!0}
+!llvm.module.flags = !{!0, !1}
diff --git a/llvm/test/Linker/module-flags-pic-2-a.ll b/llvm/test/Linker/module-flags-pic-2-a.ll
index e09af6bcd12..8898d72d510 100644
--- a/llvm/test/Linker/module-flags-pic-2-a.ll
+++ b/llvm/test/Linker/module-flags-pic-2-a.ll
@@ -1,10 +1,11 @@
-; RUN: not llvm-link %s %p/Inputs/module-flags-pic-2-b.ll -S -o - 2> %t
-; RUN: FileCheck --check-prefix=CHECK-ERRORS < %t %s
+; RUN: llvm-link %s %p/Inputs/module-flags-pic-2-b.ll -S -o - | FileCheck %s
 
-; test linking modules with two different PIC levels
+; test linking modules with two different PIC and PIE levels
 
-!0 = !{ i32 1, !"PIC Level", i32 1 }
+!0 = !{ i32 7, !"PIC Level", i32 1 }
+!1 = !{ i32 7, !"PIE Level", i32 1 }
 
-!llvm.module.flags = !{!0}
+!llvm.module.flags = !{!0, !1}
 
-; CHECK-ERRORS: ERROR: linking module flags 'PIC Level': IDs have conflicting values
+; CHECK: !0 = !{i32 7, !"PIC Level", i32 2}
+; CHECK: !1 = !{i32 7, !"PIE Level", i32 2}
diff --git a/llvm/test/Verifier/module-flags-1.ll b/llvm/test/Verifier/module-flags-1.ll
index 36bcb335ffc..ff82c284523 100644
--- a/llvm/test/Verifier/module-flags-1.ll
+++ b/llvm/test/Verifier/module-flags-1.ll
@@ -41,6 +41,10 @@
 ; CHECK-NOT: invalid value for 'append'-type module flag (expected a metadata node)
 !18 = !{i32 5, !"flag-4", !{i32 57}}
 
+; Check that any 'max' module flags are valid.
+; CHECK: invalid value for 'max' module flag (expected constant integer)
+!19 = !{i32 7, !"max", !"max"}
+
 ; Check that any 'require' module flags are valid.
 ; CHECK: invalid requirement on flag, flag is not present in module
 !11 = !{i32 3, !"bar", !{!"no-such-flag", i32 52}}
@@ -54,4 +58,4 @@
 
 !llvm.module.flags = !{
   !0, !1, !2, !3, !4, !5, !6, !7, !8, !9, !10, !11, !12, !13, !14, !15,
-  !16, !17, !18 }
+  !16, !17, !18, !19 }