[StructuralHash] Global Variable

llvm/include/llvm/IR/StructuralHash.h

@@ -31,6 +31,9 @@ class Module;
 /// to true includes instruction and operand type information.
 stable_hash StructuralHash(const Function &F, bool DetailedHash = false);
 
+/// Returns a hash of the global variable \p G.
+stable_hash StructuralHash(const GlobalVariable &G);
+
 /// Returns a hash of the module \p M by hashing all functions and global
 /// variables contained within. \param M The module to hash. \param DetailedHash
 /// Whether or not to encode additional information in the function hashes that

llvm/lib/CodeGen/MachineStableHash.cpp

@@ -27,6 +27,8 @@
 #include "llvm/CodeGen/Register.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/StructuralHash.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/Alignment.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -97,9 +99,14 @@ stable_hash llvm::stableHashValue(const MachineOperand &MO) {
       ++StableHashBailingGlobalAddress;
       return 0;
     }
-    auto Name = GV->getName();
-    return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
-                               stable_hash_name(Name), MO.getOffset());
+    stable_hash GVHash = 0;
+    if (auto *GVar = dyn_cast<GlobalVariable>(GV))
+      GVHash = StructuralHash(*GVar);
+    if (!GVHash)
+      GVHash = stable_hash_name(GV->getName());
+
+    return stable_hash_combine(MO.getType(), MO.getTargetFlags(), GVHash,
+                               MO.getOffset());
   }
 
   case MachineOperand::MO_TargetIndex: {

llvm/lib/IR/StructuralHash.cpp

@@ -46,7 +46,7 @@ class StructuralHashImpl {
   /// Assign a unique ID to each Value in the order they are first seen.
   DenseMap<const Value *, int> ValueToId;
 
-  stable_hash hashType(Type *ValueType) {
+  static stable_hash hashType(Type *ValueType) {
     SmallVector<stable_hash> Hashes;
     Hashes.emplace_back(ValueType->getTypeID());
     if (ValueType->isIntegerTy())
@@ -65,19 +65,44 @@ class StructuralHashImpl {
     }
   }
 
-  stable_hash hashAPInt(const APInt &I) {
+  static stable_hash hashAPInt(const APInt &I) {
     SmallVector<stable_hash> Hashes;
     Hashes.emplace_back(I.getBitWidth());
     auto RawVals = ArrayRef<uint64_t>(I.getRawData(), I.getNumWords());
     Hashes.append(RawVals.begin(), RawVals.end());
     return stable_hash_combine(Hashes);
   }
 
-  stable_hash hashAPFloat(const APFloat &F) {
+  static stable_hash hashAPFloat(const APFloat &F) {
     return hashAPInt(F.bitcastToAPInt());
   }
 
-  stable_hash hashGlobalValue(const GlobalValue *GV) {
+  static stable_hash hashGlobalVariable(const GlobalVariable &GVar) {
+    if (!GVar.hasInitializer())
+      return hashGlobalValue(&GVar);
+
+    // Hash the contents of a string.
+    if (GVar.getName().starts_with(".str"))
+      return hashConstant(GVar.getInitializer());
+
+    // Hash structural contents of Objective-C metadata in specific sections.
+    // This can be extended to other metadata if needed.
+    static constexpr const char *SectionNames[] = {
+        "__cfstring",      "__cstring",      "__objc_classrefs",
+        "__objc_methname", "__objc_selrefs",
+    };
+    if (GVar.hasSection()) {
+      StringRef SectionName = GVar.getSection();
+      for (const char *Name : SectionNames) {
+        if (SectionName.contains(Name))
+          return hashConstant(GVar.getInitializer());
+      }
+    }
+
+    return hashGlobalValue(&GVar);
+  }
+
+  static stable_hash hashGlobalValue(const GlobalValue *GV) {
     if (!GV->hasName())
       return 0;
     return stable_hash_name(GV->getName());
@@ -87,7 +112,7 @@ class StructuralHashImpl {
   // FunctionComparator::cmpConstants() in FunctionComparator.cpp, but here
   // we're interested in computing a hash rather than comparing two Constants.
   // Some of the logic is simplified, e.g, we don't expand GEPOperator.
-  stable_hash hashConstant(Constant *C) {
+  static stable_hash hashConstant(const Constant *C) {
     SmallVector<stable_hash> Hashes;
 
     Type *Ty = C->getType();
@@ -98,14 +123,21 @@ class StructuralHashImpl {
       return stable_hash_combine(Hashes);
     }
 
+    if (auto *GVar = dyn_cast<GlobalVariable>(C)) {
+      Hashes.emplace_back(hashGlobalVariable(*GVar));
+      return stable_hash_combine(Hashes);
+    }
+
     if (auto *G = dyn_cast<GlobalValue>(C)) {
       Hashes.emplace_back(hashGlobalValue(G));
       return stable_hash_combine(Hashes);
     }
 
     if (const auto *Seq = dyn_cast<ConstantDataSequential>(C)) {
-      Hashes.emplace_back(xxh3_64bits(Seq->getRawDataValues()));
-      return stable_hash_combine(Hashes);
+      if (Seq->isString()) {
+        Hashes.emplace_back(stable_hash_name(Seq->getAsString()));
+        return stable_hash_combine(Hashes);
+      }
     }
 
     switch (C->getValueID()) {
@@ -266,6 +298,7 @@ class StructuralHashImpl {
     Hashes.emplace_back(Hash);
     Hashes.emplace_back(GlobalHeaderHash);
     Hashes.emplace_back(GV.getValueType()->getTypeID());
+    Hashes.emplace_back(hashGlobalVariable(GV));
 
     // Update the combined hash in place.
     Hash = stable_hash_combine(Hashes);
@@ -297,6 +330,10 @@ stable_hash llvm::StructuralHash(const Function &F, bool DetailedHash) {
   return H.getHash();
 }
 
+stable_hash llvm::StructuralHash(const GlobalVariable &GVar) {
+  return StructuralHashImpl::hashGlobalVariable(GVar);
+}
+
 stable_hash llvm::StructuralHash(const Module &M, bool DetailedHash) {
   StructuralHashImpl H(DetailedHash);
   H.update(M);

llvm/test/CodeGen/AArch64/cgdata-merge-gvar.ll

@@ -0,0 +1,91 @@
+; This test verifies that global variables are hashed based on their initial contents,
+; allowing them to be merged even if they appear different due to their names.
+; Now they become identical functions that can be merged without creating a parameter.
+
+; RUN: rm -rf %t && split-file %s %t
+
+; RUN: llc -mtriple=arm64-apple-darwin -enable-global-merge-func=true -global-merging-skip-no-params=false < %t/string.ll | FileCheck %s
+; RUN: llc -mtriple=arm64-apple-darwin -enable-global-merge-func=true -global-merging-skip-no-params=false < %t/ns-const.ll | FileCheck %s
+; RUN: llc -mtriple=arm64-apple-darwin -enable-global-merge-func=true -global-merging-skip-no-params=false < %t/objc-ref.ll | FileCheck %s
+
+; CHECK: _f1.Tgm
+; CHECK: _f2.Tgm
+
+;--- string.ll
+
+@.str = private unnamed_addr constant [6 x i8] c"hello\00", align 1
+@.str.1 = private unnamed_addr constant [6 x i8] c"hello\00", align 1
+
+declare noundef i32 @goo(ptr noundef)
+
+define i32 @f1() {
+entry:
+  %call = tail call noundef i32 @goo(ptr noundef nonnull @.str)
+  %add = add nsw i32 %call, 1
+  ret i32 %add
+}
+
+define i32 @f2() {
+entry:
+  %call = tail call noundef i32 @goo(ptr noundef nonnull @.str.1)
+  %add = add nsw i32 %call, 1
+  ret i32 %add
+}
+
+;--- ns-const.ll
+
+%struct.__NSConstantString_tag = type { ptr, i32, ptr, i64 }
+@__CFConstantStringClassReference = external global [0 x i32]
+@.str.2 = private unnamed_addr constant [9 x i8] c"cfstring\00", section "__TEXT,__cstring,cstring_literals", align 1
+@_unnamed_cfstring_ = private global %struct.__NSConstantString_tag { ptr @__CFConstantStringClassReference, i32 1992, ptr @.str.2, i64 8 }, section "__DATA,__cfstring", align 8
+
+@.str.3 = private unnamed_addr constant [9 x i8] c"cfstring\00", section "__TEXT,__cstring,cstring_literals", align 1
+@_unnamed_cfstring_.2 = private global %struct.__NSConstantString_tag { ptr @__CFConstantStringClassReference, i32 1992, ptr @.str.3, i64 8 }, section "__DATA,__cfstring", align 8
+
+declare noundef i32 @hoo(ptr noundef)
+
+define i32 @f1() {
+entry:
+  %call = tail call i32 @hoo(ptr noundef nonnull @_unnamed_cfstring_)
+  %add = sub nsw i32 %call, 1
+  ret i32 %add
+}
+
+define i32 @f2() {
+entry:
+  %call = tail call i32 @hoo(ptr noundef nonnull @_unnamed_cfstring_.2)
+  %add = sub nsw i32 %call, 1
+  ret i32 %add
+}
+
+;--- objc-ref.ll
+
+%struct._class_t = type { ptr, ptr, ptr, ptr, ptr }
+
+@"OBJC_CLASS_$_MyClass" = external global %struct._class_t
+@"OBJC_CLASSLIST_REFERENCES_$_" = internal global ptr @"OBJC_CLASS_$_MyClass", section "__DATA,__objc_classrefs,regular,no_dead_strip", align 8
+@"OBJC_CLASSLIST_REFERENCES_$_.1" = internal global ptr @"OBJC_CLASS_$_MyClass", section "__DATA,__objc_classrefs,regular,no_dead_strip", align 8
+
+@OBJC_METH_VAR_NAME_ = private unnamed_addr constant [6 x i8] c"hello\00", section "__TEXT,__objc_methname,cstring_literals", align 1
+@OBJC_METH_VAR_NAME_.1 = private unnamed_addr constant [6 x i8] c"hello\00", section "__TEXT,__objc_methname,cstring_literals", align 1
+
+@OBJC_SELECTOR_REFERENCES_ = internal externally_initialized global ptr @OBJC_METH_VAR_NAME_, section "__DATA,__objc_selrefs,literal_pointers,no_dead_strip", align 8
+@OBJC_SELECTOR_REFERENCES_.1 = internal externally_initialized global ptr @OBJC_METH_VAR_NAME_.1, section "__DATA,__objc_selrefs,literal_pointers,no_dead_strip", align 8
+
+define i32 @f1() {
+entry:
+  %0 = load ptr, ptr @"OBJC_CLASSLIST_REFERENCES_$_", align 8
+  %1 = load ptr, ptr @OBJC_SELECTOR_REFERENCES_, align 8
+  %call = tail call noundef i32 @objc_msgSend(ptr noundef %0, ptr noundef %1)
+  ret i32 %call
+}
+
+declare ptr @objc_msgSend(ptr, ptr, ...)
+
+define i32 @f2() {
+entry:
+  %0 = load ptr, ptr @"OBJC_CLASSLIST_REFERENCES_$_.1", align 8
+  %1 = load ptr, ptr @OBJC_SELECTOR_REFERENCES_.1, align 8
+  %call = tail call noundef i32 @objc_msgSend(ptr noundef %0, ptr noundef %1)
+  ret i32 %call
+}

llvm/test/CodeGen/AArch64/cgdata-outline-gvar.ll

@@ -0,0 +1,52 @@
+; This test verifies that global variables are hashed based on their initial contents,
+; allowing them to be outlined even if they appear different due to their names.
+
+; RUN: split-file %s %t
+
+; Check if the outlined function is created locally.
+; RUN: llc -mtriple=arm64-apple-darwin -enable-machine-outliner -codegen-data-generate=true  -aarch64-enable-collect-loh=false -filetype=obj %t/local-two.ll -o %t_write_base
+; RUN: llvm-objdump -d %t_write_base | FileCheck %s
+
+; RUN: llvm-cgdata --merge %t_write_base -o %t_cgdata_base
+
+; Read the cgdata in the machine outliner for optimistically outlining in local-one.ll.
+; RUN: llc -mtriple=arm64-apple-darwin -enable-machine-outliner -codegen-data-use-path=%t_cgdata_base  -aarch64-enable-collect-loh=false -append-content-hash-outlined-name=false -filetype=obj %t/local-one.ll -o %t_read_base
+; RUN: llvm-objdump -d %t_read_base | FileCheck %s
+
+; The names of globals `.str` and `.str.4` are different, but their initial contents are identical.
+; The outlined function now starts with a reference to that global ("hello\00").
+; CHECK: _OUTLINED_FUNCTION_{{.*}}:
+; CHECK-NEXT: adrp x1
+; CHECK-NEXT: add x1, x1
+; CHECK-NEXT: mov w2
+; CHECK-NEXT: mov w3
+; CHECK-NEXT: mov w4
+; CHECK-NEXT: b
+
+;--- local-two.ll
+@.str = private unnamed_addr constant [6 x i8] c"hello\00", align 1
+@.str.1 = private unnamed_addr constant [3 x i8] c"f1\00", align 1
+@.str.2 = private unnamed_addr constant [3 x i8] c"f2\00", align 1
+
+declare noundef i32 @goo(ptr noundef, ptr noundef, i32, i32, i32)
+define i32 @f1() minsize {
+entry:
+  %call = tail call noundef i32 @goo(ptr noundef nonnull @.str.1, ptr noundef nonnull @.str, i32 1, i32 2, i32 3)
+  ret i32 %call
+}
+define i32 @f2() minsize {
+entry:
+  %call = tail call noundef i32 @goo(ptr noundef nonnull @.str.2, ptr noundef nonnull @.str, i32 1, i32 2, i32 3)
+  ret i32 %call
+}
+
+;--- local-one.ll
+@.str.3 = private unnamed_addr constant [3 x i8] c"f3\00", align 1
+@.str.4 = private unnamed_addr constant [6 x i8] c"hello\00", align 1
+
+declare noundef i32 @goo(ptr noundef, ptr noundef, i32, i32, i32)
+define i32 @f1() minsize {
+entry:
+  %call = tail call noundef i32 @goo(ptr noundef nonnull @.str.3, ptr noundef nonnull @.str.4, i32 1, i32 2, i32 3)
+  ret i32 %call
+}