Support for taking the max of module flags when linking, use for PIE/PIC

Summary:
Add Max ModFlagBehavior, which can be used to take the max of two
module flag values when merging modules. Use it for the PIE and PIC
levels.

This avoids an error when we try to import from a module built -fpic
into a module built -fPIC, for example. For both PIE and PIC levels,
this will be legal, since the code generation gets more conservative
as the level is increased. Therefore we can take the max instead of
somehow trying to block importing between modules compiled with
different levels.

Reviewers: tmsriram, pcc

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33418

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303590 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/IR/Module.h b/include/llvm/IR/Module.h
index 3024d9e27a2fc3189a0af4a28de7314abd798ea6..5e1f680c5b3675c6604a45e561517fb8f5eddb0c 100644 (file)
--- a/include/llvm/IR/Module.h
+++ b/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/lib/IR/Module.cpp b/lib/IR/Module.cpp
index 12c258d95f52302fc207b361f9cae6928092f7d6..95673e515a5591c9760e6b8253930289d74405d5 100644 (file)
--- a/lib/IR/Module.cpp
+++ b/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/lib/IR/Verifier.cpp b/lib/IR/Verifier.cpp
index 21e8048442beb79dca205b4cb66e248c7c926a1e..ffb9ad27922d89fe3de17b813ea73bb8f830c384 100644 (file)
--- a/lib/IR/Verifier.cpp
+++ b/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/lib/Linker/IRMover.cpp b/lib/Linker/IRMover.cpp
index c0af21aa148c302d1ee7cc28637d5c53aafbec60..defad1904989d2d0c037ffa9398714f2752c73a8 100644 (file)
--- a/lib/Linker/IRMover.cpp
+++ b/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/test/Linker/Inputs/module-flags-pic-2-b.ll b/test/Linker/Inputs/module-flags-pic-2-b.ll
index 0d78cafc6a0f4da025d50eb442a32af28159af8b..f652eddb3842fda19d224e15822903845571a096 100644 (file)
--- a/test/Linker/Inputs/module-flags-pic-2-b.ll
+++ b/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/test/Linker/module-flags-pic-2-a.ll b/test/Linker/module-flags-pic-2-a.ll
index e09af6bcd12830b8b7d7b72265ac1093581f9f7c..8898d72d51016b45d9ee94583bbbbc357ef08c68 100644 (file)
--- a/test/Linker/module-flags-pic-2-a.ll
+++ b/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/test/Verifier/module-flags-1.ll b/test/Verifier/module-flags-1.ll
index 36bcb335ffc21bdcfe044e58d28d5a5762fca904..ff82c2845235a50f8257af84bbab29d50d6b9356 100644 (file)
--- a/test/Verifier/module-flags-1.ll
+++ b/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 }