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, 12 insertions, 0 deletions

diff --git a/Source/cmMakefileExecutableTargetGenerator.cxx b/Source/cmMakefileExecutableTargetGenerator.cxx
index 9d42257..ba4c6e6 100644
--- a/Source/cmMakefileExecutableTargetGenerator.cxx
+++ b/Source/cmMakefileExecutableTargetGenerator.cxx
@@ -187,6 +187,9 @@ void cmMakefileExecutableTargetGenerator::WriteExecutableRule(bool relink)
     this->LocalGenerator->AppendFlags(
       linkFlags, this->Makefile->GetDefinition(export_flag_var));
   }
+  if (this->GeneratorTarget->GetProperty("LINK_WHAT_YOU_USE")) {
+    this->LocalGenerator->AppendFlags(linkFlags, " -Wl,--no-as-needed");
+  }
 
   // Add language feature flags.
   this->AddFeatureFlags(flags, linkLanguage);
@@ -356,6 +359,15 @@ void cmMakefileExecutableTargetGenerator::WriteExecutableRule(bool relink)
     vars.LinkFlags = linkFlags.c_str();
     vars.Manifests = manifests.c_str();
 
+    if (this->GeneratorTarget->GetProperty("LINK_WHAT_YOU_USE")) {
+      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 in the commands.
     this->LocalGenerator->TargetImplib = targetOutPathImport;
     for (std::vector<std::string>::iterator i = real_link_commands.begin();