From 9306ef9750b7a319d59f6d3e4977e01e39b8f161 Mon Sep 17 00:00:00 2001
From: Dhruv Chawla <dhruv263.dc@gmail.com>
Date: Mon, 6 Mar 2023 08:16:16 -0800
Subject: [clang][alias|ifunc]: Add a diagnostic for mangled names

When an alias or ifunc attribute refers to a function name that is
mangled, a diagnostic is emitted to suggest the mangled name as a
replacement for the given function name for every matching name in the
current TU.

Fixes #59164

Differential Revision: https://reviews.llvm.org/D143803
---
 clang/lib/CodeGen/CodeGenModule.cpp | 34 +++++++++++++++++++++++++++-------
 1 file changed, 27 insertions(+), 7 deletions(-)

(limited to 'clang/lib/CodeGen/CodeGenModule.cpp')

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 90c9df4ea442..b512fb576a2c 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -338,10 +338,11 @@ static const llvm::GlobalValue *getAliasedGlobal(const llvm::GlobalValue *GV) {
   return FinalGV;
 }
 
-static bool checkAliasedGlobal(DiagnosticsEngine &Diags,
-                               SourceLocation Location, bool IsIFunc,
-                               const llvm::GlobalValue *Alias,
-                               const llvm::GlobalValue *&GV) {
+static bool checkAliasedGlobal(
+    DiagnosticsEngine &Diags, SourceLocation Location, bool IsIFunc,
+    const llvm::GlobalValue *Alias, const llvm::GlobalValue *&GV,
+    const llvm::MapVector<GlobalDecl, StringRef> &MangledDeclNames,
+    SourceRange AliasRange) {
   GV = getAliasedGlobal(Alias);
   if (!GV) {
     Diags.Report(Location, diag::err_cyclic_alias) << IsIFunc;
@@ -350,6 +351,22 @@ static bool checkAliasedGlobal(DiagnosticsEngine &Diags,
 
   if (GV->isDeclaration()) {
     Diags.Report(Location, diag::err_alias_to_undefined) << IsIFunc << IsIFunc;
+    Diags.Report(Location, diag::note_alias_requires_mangled_name)
+        << IsIFunc << IsIFunc;
+    // Provide a note if the given function is not found and exists as a
+    // mangled name.
+    for (const auto &[Decl, Name] : MangledDeclNames) {
+      if (const auto *ND = dyn_cast<NamedDecl>(Decl.getDecl())) {
+        if (ND->getName() == GV->getName()) {
+          Diags.Report(Location, diag::note_alias_mangled_name_alternative)
+              << Name
+              << FixItHint::CreateReplacement(
+                     AliasRange,
+                     (Twine(IsIFunc ? "ifunc" : "alias") + "(\"" + Name + "\")")
+                         .str());
+        }
+      }
+    }
     return false;
   }
 
@@ -381,16 +398,19 @@ void CodeGenModule::checkAliases() {
   for (const GlobalDecl &GD : Aliases) {
     const auto *D = cast<ValueDecl>(GD.getDecl());
     SourceLocation Location;
+    SourceRange Range;
     bool IsIFunc = D->hasAttr<IFuncAttr>();
-    if (const Attr *A = D->getDefiningAttr())
+    if (const Attr *A = D->getDefiningAttr()) {
       Location = A->getLocation();
-    else
+      Range = A->getRange();
+    } else
       llvm_unreachable("Not an alias or ifunc?");
 
     StringRef MangledName = getMangledName(GD);
     llvm::GlobalValue *Alias = GetGlobalValue(MangledName);
     const llvm::GlobalValue *GV = nullptr;
-    if (!checkAliasedGlobal(Diags, Location, IsIFunc, Alias, GV)) {
+    if (!checkAliasedGlobal(Diags, Location, IsIFunc, Alias, GV,
+                            MangledDeclNames, Range)) {
       Error = true;
       continue;
     }
-- 
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