[IRMover] Improve diagnostic messages for conflicting metadata

[ikudrin]

Summary

This does the similar for error messages as D52952 has done for warnings.

With llvm::lto::LTO, the error might appear when LTO::run() is executed. In that case, the calling code cannot know which module causes the error and, subsequently, cannot hint the user.

[dblaikie]

Seems reasonable - thanks!

lib/Linker/IRMover.cpp

for (unsigned I = 0, E = SrcModFlags->getNumOperands(); I != E; ++I) {
     };
 
     // If either flag has override behavior, handle it first.
     if (DstBehaviorValue == Module::Override) {
       // Diagnose inconsistent flags which both have override behavior.
       if (SrcBehaviorValue == Module::Override &&
           SrcOp->getOperand(2) != DstOp->getOperand(2))
         return stringErr("linking module flags '" + ID->getString() +
-                         "': IDs have conflicting override values");
+                         "': IDs have conflicting override values in '" +
+                         SrcM->getModuleIdentifier() + "' and '" +
+                         DstM.getModuleIdentifier() + "'");
       continue;
     } else if (SrcBehaviorValue == Module::Override) {
       // Update the destination flag to that of the source.
       overrideDstValue();
       continue;
     }
 
     // Diagnose inconsistent merge behavior types.
     if (SrcBehaviorValue != DstBehaviorValue)
       return stringErr("linking module flags '" + ID->getString() +
-                       "': IDs have conflicting behaviors");
+                       "': IDs have conflicting behaviors in '" +
+                       SrcM->getModuleIdentifier() + "' and '" +
+                       DstM.getModuleIdentifier() + "'");
 
     auto replaceDstValue = [&](MDNode *New) {
       Metadata *FlagOps[] = {DstOp->getOperand(0), ID, New};
       MDNode *Flag = MDNode::get(DstM.getContext(), FlagOps);
       DstModFlags->setOperand(DstIndex, Flag);
       Flags[ID].first = Flag;
     };
 
     // Perform the merge for standard behavior types.
     switch (SrcBehaviorValue) {
     case Module::Require:
     case Module::Override:
       llvm_unreachable("not possible");
     case Module::Error: {
       // Emit an error if the values differ.
       if (SrcOp->getOperand(2) != DstOp->getOperand(2))
         return stringErr("linking module flags '" + ID->getString() +
-                         "': IDs have conflicting values");
+                         "': IDs have conflicting values in '" +
+                         SrcM->getModuleIdentifier() + "' and '" +
+                         DstM.getModuleIdentifier() + "'");
       continue;
     }
     case Module::Warning: {
       // Emit a warning if the values differ.
       if (SrcOp->getOperand(2) != DstOp->getOperand(2)) {
         std::string str;
         raw_string_ostream(str)
             << "linking module flags '" << ID->getString()

test/Linker/module-flags-5-a.ll

 ; RUN: not llvm-link %s %p/module-flags-5-b.ll -S -o - 2>&1 | FileCheck %s
 
 ; Test the 'override' error.
 
-; CHECK: linking module flags 'foo': IDs have conflicting override values
+; CHECK: linking module flags 'foo': IDs have conflicting override values in '{{.*}}module-flags-5-b.ll' and 'llvm-link'
 
 !0 = !{ i32 4, !"foo", i32 927 }
 
 !llvm.module.flags = !{ !0 }

test/Linker/module-flags-6-a.ll

 ; RUN: not llvm-link %s %p/module-flags-6-b.ll -S -o - 2>&1 | FileCheck %s
 
 ; Test module flags error messages.
 
-; CHECK: linking module flags 'foo': IDs have conflicting values
+; CHECK: linking module flags 'foo': IDs have conflicting values in '{{.*}}module-flags-6-b.ll' and 'llvm-link'
 
 !0 = !{ i32 1, !"foo", i32 37 }
 
 !llvm.module.flags = !{ !0 }

test/Linker/module-flags-7-a.ll

 ; RUN: not llvm-link %s %p/module-flags-7-b.ll -S -o - 2>&1 | FileCheck %s
 
 ; Test module flags error messages.
 
-; CHECK: linking module flags 'foo': IDs have conflicting behaviors
+; CHECK: linking module flags 'foo': IDs have conflicting behaviors in '{{.*}}module-flags-7-b.ll' and 'llvm-link'
 
 !0 = !{ i32 1, !"foo", i32 37 }
 
 !llvm.module.flags = !{ !0 }