[llvm_stats] Do not import llvm.stats metadata for thinlto

The stats are computed per module and will all be merged in the binary, importing the metadata will cause duplication of the stats.

Reviewed By: hoy, wenlei

Differential Revision: https://reviews.llvm.org/D138833

llvm/lib/Linker/IRMover.cpp

@@ -1244,6 +1244,11 @@ void IRLinker::linkNamedMDNodes() {
                     DstM.getModuleIdentifier() + "' is not\n");
       continue;
     }
+    // The stats are computed per module and will all be merged in the binary.
+    // Importing the metadata will cause duplication of the stats.
+    if (IsPerformingImport && NMD.getName() == "llvm.stats")
+      continue;
+
     NamedMDNode *DestNMD = DstM.getOrInsertNamedMetadata(NMD.getName());
     // Add Src elements into Dest node.
     for (const MDNode *Op : NMD.operands())

llvm/test/ThinLTO/X86/Inputs/llvm-stats-import.ll

@@ -0,0 +1,12 @@
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @foo() {
+entry:
+  ret void
+}
+
+attributes #0 = { inaccessiblememonly nounwind willreturn }
+
+!llvm.stats = !{!0}
+!0 = !{!"foo", i64 456}

llvm/test/ThinLTO/X86/llvm-stats-import.ll

@@ -0,0 +1,28 @@
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/llvm-stats-import.ll -o %t2.bc
+; RUN: llvm-lto -thinlto-action=thinlink -o %t.index.bc %t1.bc %t2.bc
+
+; RUN: llvm-lto -thinlto-action=import %t1.bc -thinlto-index=%t.index.bc -o - | llvm-dis -o - | FileCheck %s --check-prefix=CHECK-MAIN
+; RUN: llvm-lto -thinlto-action=import %t2.bc -thinlto-index=%t.index.bc -o - | llvm-dis -o - | FileCheck %s --check-prefix=CHECK-FOO
+
+; CHECK-MAIN: !0 = !{!"main", i64 123}
+; CHECK-MAIN-NOT: !{!"foo", i64 456}
+
+; CHECK-FOO: !0 = !{!"foo", i64 456}
+; CHECK-FOO-NOT: !{!"main", i64 123}
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @main() {
+entry:
+  call void (...) @foo()
+  ret i32 0
+}
+
+declare void @foo(...)
+
+attributes #0 = { inaccessiblememonly nounwind willreturn }
+
+!llvm.stats = !{!0}
+!0 = !{!"main", i64 123}