[clang] Fix crash with -funique-internal-linkage-names

[ellis]

Summary

Calling getFunctionLinkage(CalleeInfo.getCalleeDecl()) will crash when the declaration does not have a body, e.g., extern void foo();. Instead, we can use isExternallyVisible() to see if the delcaration has internal linkage.

I believe using !isExternallyVisible() is correct because the clang linkage must be InternalLinkage or UniqueExternalLinkage, both of which are "internal linkage" in llvm.
https://github.com/llvm/llvm-project/blob/9c26f51f5e178ac0fda98419e3a61d205d3b58b1/clang/include/clang/Basic/Linkage.h#L28-L40

Fixes https://github.com/llvm/llvm-project/issues/54139

[tmsriram]

LGTM, thanks for fixing this!

clang/lib/CodeGen/CGCall.cpp

if (CodeGenOpts.NoPLT) {
         }
       }
     }
   }
 
   // Add "sample-profile-suffix-elision-policy" attribute for internal linkage
   // functions with -funique-internal-linkage-names.
   if (TargetDecl && CodeGenOpts.UniqueInternalLinkageNames) {
-    if (isa<FunctionDecl>(TargetDecl)) {
-      if (this->getFunctionLinkage(CalleeInfo.getCalleeDecl()) ==
-          llvm::GlobalValue::InternalLinkage)
+    if (const auto *FD = dyn_cast_or_null<FunctionDecl>(TargetDecl)) {
+      if (!FD->isExternallyVisible())
         FuncAttrs.addAttribute("sample-profile-suffix-elision-policy",
                                "selected");
     }
   }
 
   // Collect non-call-site function IR attributes from declaration-specific
   // information.
   if (!AttrOnCallSite) {

clang/test/CodeGen/unique-internal-linkage-names.c

+// RUN: %clang_cc1 %s -S -emit-llvm -funique-internal-linkage-names -o - | FileCheck %s
+
+// Check that we do not crash when overloading extern functions.
+
+inline void overloaded_external() {}
+extern void overloaded_external();
+
+// CHECK: define internal void @overloaded_internal() [[ATTR:#[0-9]+]] {
+static void overloaded_internal() {}
+extern void overloaded_internal();
+
+void markUsed() {
+  overloaded_external();
+  overloaded_internal();
+}
+
+// CHECK: attributes [[ATTR]] =
+// CHECK-SAME: "sample-profile-suffix-elision-policy"="selected"