Add options to run `ldd -u -r` as a "link-what-you-use" tool

Create a LINK_WHAT_YOU_USE target property and corresponding
CMAKE_LINK_WHAT_YOU_USE variable to enable this behavior.
Extend link commands by running `ldd -u -r` to detect shared
libraries that are linked but not needed.

1 files changed, 13 insertions, 0 deletions

diff --git a/Source/cmMakefileLibraryTargetGenerator.cxx b/Source/cmMakefileLibraryTargetGenerator.cxx
index 128291d..6666c36 100644
--- a/Source/cmMakefileLibraryTargetGenerator.cxx
+++ b/Source/cmMakefileLibraryTargetGenerator.cxx
@@ -163,6 +163,9 @@ void cmMakefileLibraryTargetGenerator::WriteSharedLibraryRules(bool relink)
     extraFlags, "CMAKE_SHARED_LINKER_FLAGS", this->ConfigName);
   this->AddModuleDefinitionFlag(extraFlags);
 
+  if (this->GeneratorTarget->GetProperty("LINK_WHAT_YOU_USE")) {
+    this->LocalGenerator->AppendFlags(extraFlags, " -Wl,--no-as-needed");
+  }
   this->WriteLibraryRules(linkRuleVar, extraFlags, relink);
 }
 
@@ -682,6 +685,15 @@ void cmMakefileLibraryTargetGenerator::WriteLibraryRules(
       // Get the set of commands.
       std::string linkRule = this->GetLinkRule(linkRuleVar);
       cmSystemTools::ExpandListArgument(linkRule, real_link_commands);
+      if (this->GeneratorTarget->GetProperty("LINK_WHAT_YOU_USE") &&
+          (this->GeneratorTarget->GetType() == cmState::SHARED_LIBRARY)) {
+        std::string cmakeCommand =
+          this->Convert(cmSystemTools::GetCMakeCommand(),
+                        cmLocalGenerator::NONE, cmLocalGenerator::SHELL);
+        cmakeCommand += " -E __run_iwyu --lwyu=";
+        cmakeCommand += targetOutPathReal;
+        real_link_commands.push_back(cmakeCommand);
+      }
 
       // Expand placeholders.
       for (std::vector<std::string>::iterator i = real_link_commands.begin();
@@ -728,6 +740,7 @@ void cmMakefileLibraryTargetGenerator::WriteLibraryRules(
     commands.insert(commands.end(), commands1.begin(), commands1.end());
     commands1.clear();
   }
+
   // Add the post-build rules when building but not when relinking.
   if (!relink) {
     this->LocalGenerator->AppendCustomCommands(