[IR] Add "Large Data Threshold" module metadata

llvm/include/llvm/IR/Module.h

@@ -922,6 +922,17 @@ class LLVM_EXTERNAL_VISIBILITY Module {
   void setCodeModel(CodeModel::Model CL);
   /// @}
 
+  /// @}
+  /// @name Utility function for querying and setting the large data threshold
+  /// @{
+
+  /// Returns the code model (tiny, small, kernel, medium or large model)
+  std::optional<uint64_t> getLargeDataThreshold() const;
+
+  /// Set the code model (tiny, small, kernel, medium or large)
+  void setLargeDataThreshold(uint64_t Threshold);
+  /// @}
+
   /// @name Utility functions for querying and setting PGO summary
   /// @{
 

llvm/lib/IR/Module.cpp

@@ -631,6 +631,23 @@ void Module::setCodeModel(CodeModel::Model CL) {
   addModuleFlag(ModFlagBehavior::Error, "Code Model", CL);
 }
 
+std::optional<uint64_t> Module::getLargeDataThreshold() const {
+  auto *Val =
+      cast_or_null<ConstantAsMetadata>(getModuleFlag("Large Data Threshold"));
+
+  if (!Val)
+    return std::nullopt;
+
+  return cast<ConstantInt>(Val->getValue())->getZExtValue();
+}
+
+void Module::setLargeDataThreshold(uint64_t Threshold) {
+  // Since the large data threshold goes along with the code model, the merge
+  // behavior is the same.
+  addModuleFlag(ModFlagBehavior::Error, "Large Data Threshold",
+                ConstantInt::get(Type::getInt64Ty(Context), Threshold));
+}
+
 void Module::setProfileSummary(Metadata *M, ProfileSummary::Kind Kind) {
   if (Kind == ProfileSummary::PSK_CSInstr)
     setModuleFlag(ModFlagBehavior::Error, "CSProfileSummary", M);

llvm/lib/LTO/LTOBackend.cpp

@@ -225,7 +225,12 @@ createTargetMachine(const Config &Conf, const Target *TheTarget, Module &M) {
   std::unique_ptr<TargetMachine> TM(TheTarget->createTargetMachine(
       TheTriple, Conf.CPU, Features.getString(), Conf.Options, RelocModel,
       CodeModel, Conf.CGOptLevel));
+
   assert(TM && "Failed to create target machine");
+
+  if (std::optional<uint64_t> LargeDataThreshold = M.getLargeDataThreshold())
+    TM->setLargeDataThreshold(*LargeDataThreshold);
+
   return TM;
 }
 

llvm/test/LTO/X86/Inputs/largedatathreshold.ll

@@ -0,0 +1,10 @@
+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"
+
+define void @bar() {
+  ret void
+}
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 1, !"Code Model", i32 3}
+!1 = !{i32 1, !"Large Data Threshold", i32 101}

llvm/test/LTO/X86/largedatathreshold-1.ll

@@ -0,0 +1,21 @@
+; RUN: llvm-as %s -o %t.o
+; RUN: llvm-lto2 run -r %t.o,_start,px %t.o -o %t.s
+; RUN: llvm-objdump -d %t.s.0 | FileCheck %s
+
+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"
+
+@data = internal constant [20 x i8] zeroinitializer
+
+define ptr @_start() {
+entry:
+; CHECK-LABEL:  <_start>:
+; CHECK: leaq    (%rip), %rax
+; CHECK-NOT: movabsq
+    ret ptr @data
+}
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 1, !"Code Model", i32 3}
+!1 = !{i32 1, !"Large Data Threshold", i32 100}

llvm/test/LTO/X86/largedatathreshold-2.ll

@@ -0,0 +1,20 @@
+; RUN: llvm-as %s -o %t.o
+; RUN: llvm-lto2 run -r %t.o,_start,px %t.o -o %t.s
+; RUN: llvm-objdump -d %t.s.0 | FileCheck %s
+
+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"
+
+@data = internal constant [20 x i8] zeroinitializer
+
+define ptr @_start() {
+entry:
+; CHECK-LABEL:  <_start>:
+; CHECK: movabsq $0x0, %rax
+    ret ptr @data
+}
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 1, !"Code Model", i32 3}
+!1 = !{i32 1, !"Large Data Threshold", i32 10}

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

@@ -0,0 +1,20 @@
+; RUN: llvm-as %s -o %t0.o
+; RUN: llvm-as < %p/Inputs/largedatathreshold.ll > %t1.o
+; RUN: not llvm-lto2 run -r %t0.o,_start,px -r %t1.o,bar,px %t0.o %t1.o -o %t2.s 2>&1 | FileCheck %s
+
+; CHECK: 'Large Data Threshold': IDs have conflicting values
+
+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"
+
+@data = internal constant [20 x i8] zeroinitializer
+
+define ptr @_start() {
+entry:
+  ret ptr @data
+}
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 1, !"Code Model", i32 3}
+!1 = !{i32 1, !"Large Data Threshold", i32 100}