[LTO] Print conflicting operands between Src and Dest modules

llvm/lib/Linker/IRMover.cpp

@@ -1430,11 +1430,15 @@ Error IRLinker::linkModuleFlagsMetadata() {
       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 in '" +
-                         SrcM->getModuleIdentifier() + "' and '" +
-                         DstM.getModuleIdentifier() + "'");
+      if (SrcOp->getOperand(2) != DstOp->getOperand(2)) {
+        std::string Str;
+        raw_string_ostream(Str)
+            << "linking module flags '" << ID->getString()
+            << "': IDs have conflicting values: '" << *SrcOp->getOperand(2)
+            << "' from " << SrcM->getModuleIdentifier() << ", and '"
+            << *DstOp->getOperand(2) << "' from " + DstM.getModuleIdentifier();
+        return stringErr(Str);
+      }
       continue;
     }
     case Module::Warning: {

llvm/test/LTO/X86/codemodel-3.ll

@@ -18,4 +18,4 @@ entry:
     ret ptr @data
 }
 
-; CHECK: 'Code Model': IDs have conflicting values
+; CHECK: 'Code Model': IDs have conflicting values: 'i32 1' from {{.*}}, and 'i32 4' from {{.*}}

llvm/test/LTO/X86/largedatathreshold-3.ll

@@ -3,7 +3,7 @@
 ; RUN: not llvm-lto2 run -r %t0.o,_start,px -r %t1.o,bar,px -r %t0.o,_GLOBAL_OFFSET_TABLE_, \
 ; RUN:   -r %t1.o,_GLOBAL_OFFSET_TABLE_, %t0.o %t1.o -o %t2.s 2>&1 | FileCheck %s
 
-; CHECK: 'Large Data Threshold': IDs have conflicting values
+; CHECK: 'Large Data Threshold': IDs have conflicting values: 'i32 101' from {{.*}}, and 'i32 100' from {{.*}}
 
 target triple = "x86_64-unknown-linux-gnu"
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"

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

@@ -2,7 +2,7 @@
 
 ; Test module flags error messages.
 
-; CHECK: linking module flags 'foo': IDs have conflicting values in '{{.*}}module-flags-6-b.ll' and 'llvm-link'
+; CHECK: linking module flags 'foo': IDs have conflicting values: 'i32 38' from {{.*}}module-flags-6-b.ll, and 'i32 37' from llvm-link
 
 !0 = !{ i32 1, !"foo", i32 37 }
 

llvm/test/Transforms/FunctionImport/module-flags.ll

@@ -4,7 +4,7 @@
 ; RUN: llvm-lto -thinlto -o 3 1.bc 2.bc
 ; RUN: opt -S -passes=function-import -summary-file 3.thinlto.bc 1.bc 2>&1 | FileCheck %s
 
-; CHECK: Function Import: link error: linking module flags 'Error': IDs have conflicting values in '2.bc' and '1.bc'
+; CHECK: Function Import: link error: linking module flags 'Error': IDs have conflicting values: 'i32 1' from 2.bc, and 'i32 0' from 1.bc
 
 ;--- 1.ll
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"