[ThinLTO] Import symver directives for imported symbols (PR48214)

When importing symbols from another module, also import any
corresponding symver directives.

Differential revision: https://reviews.llvm.org/D92335

llvm/lib/Linker/CMakeLists.txt

@@ -10,6 +10,7 @@ add_llvm_component_library(LLVMLinker
 
   LINK_COMPONENTS
   Core
+  Object
   Support
   TransformUtils
   )

llvm/lib/Linker/IRMover.cpp

@@ -17,6 +17,7 @@
 #include "llvm/IR/GVMaterializer.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/TypeFinder.h"
+#include "llvm/Object/ModuleSymbolTable.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include <utility>
@@ -1438,12 +1439,6 @@ Error IRLinker::run() {
 
   DstM.setTargetTriple(SrcTriple.merge(DstTriple));
 
-  // Append the module inline asm string.
-  if (!IsPerformingImport && !SrcM->getModuleInlineAsm().empty()) {
-    DstM.appendModuleInlineAsm(adjustInlineAsm(SrcM->getModuleInlineAsm(),
-                                               SrcTriple));
-  }
-
   // Loop over all of the linked values to compute type mappings.
   computeTypeMapping();
 
@@ -1474,6 +1469,24 @@ Error IRLinker::run() {
   // are properly remapped.
   linkNamedMDNodes();
 
+  if (!IsPerformingImport && !SrcM->getModuleInlineAsm().empty()) {
+    // Append the module inline asm string.
+    DstM.appendModuleInlineAsm(adjustInlineAsm(SrcM->getModuleInlineAsm(),
+                                               SrcTriple));
+  } else if (IsPerformingImport) {
+    // Import any symver directives for symbols in DstM.
+    ModuleSymbolTable::CollectAsmSymvers(*SrcM,
+                                         [&](StringRef Name, StringRef Alias) {
+      if (DstM.getNamedValue(Name)) {
+        SmallString<256> S(".symver ");
+        S += Name;
+        S += ", ";
+        S += Alias;
+        DstM.appendModuleInlineAsm(S);
+      }
+    });
+  }
+
   // Merge the module flags into the DstM module.
   return linkModuleFlagsMetadata();
 }

llvm/test/ThinLTO/X86/Inputs/import-symver-foo.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"
+
+module asm ".symver bar, bar@BAR_1.2.3"
+
+declare dso_local i32 @bar()
+
+define dso_local i32 @foo() {
+entry:
+  %call = tail call i32 @bar()
+  ret i32 %call
+}

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

@@ -0,0 +1,28 @@
+; RUN: opt -thinlto-bc %s -o %t1.bc
+; RUN: opt -thinlto-bc %p/Inputs/import-symver-foo.ll -o %t2.bc
+; RUN: llvm-lto -thinlto-action=thinlink %t1.bc %t2.bc -o %t3.index.bc
+
+; RUN: llvm-lto -thinlto-action=import -exported-symbol=main %t1.bc -thinlto-index=%t3.index.bc
+; RUN: llvm-dis %t1.bc.thinlto.imported.bc -o - | FileCheck --check-prefix=IMPORT %s
+
+; RUN: llvm-lto -thinlto-action=import -exported-symbol=main -import-instr-limit=0 %t1.bc -thinlto-index=%t3.index.bc
+; RUN: llvm-dis %t1.bc.thinlto.imported.bc -o - | FileCheck --check-prefix=NOIMPORT %s
+
+; When @bar gets imported, the symver must be imported too.
+; IMPORT: module asm ".symver bar, bar@BAR_1.2.3"
+; IMPORT: declare dso_local i32 @bar()
+
+; When @bar isn't imported, the symver is also not imported.
+; NOIMPORT-NOT: module asm
+; NOIMPORT-NOT: declare dso_local i32 @bar()
+
+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"
+
+declare dso_local i32 @foo()
+
+define dso_local i32 @main() {
+entry:
+  %call = tail call i32 @foo()
+  ret i32 %call
+}

llvm/utils/gn/secondary/llvm/lib/Linker/BUILD.gn

@@ -2,6 +2,7 @@ static_library("Linker") {
   output_name = "LLVMLinker"
   deps = [
     "//llvm/lib/IR",
+    "//llvm/lib/Object",
     "//llvm/lib/Support",
     "//llvm/lib/Transforms/Utils",
   ]