Genex: Optimize usage requirement TARGET_PROPERTY recursion

In large projects the generation process spends a lot of time evaluating
usage requirements through transitive interface properties on targets.
This can be seen in a contrived example with deep dependencies:

    set(prev "")
    foreach(i RANGE 1 500)
      add_library(a${i} a.c)
      target_compile_definitions(a${i} PUBLIC A${i})
      target_link_libraries(a${i} PUBLIC ${prev})
      set(prev a${i})
    endforeach()

For each usage requirement (such as `INTERFACE_COMPILE_DEFINITIONS` or
`INTERFACE_INCLUDE_DIRECTORIES`), the value of the generator expression
`$<TARGET_PROPERTY:target,prop>` includes the values of the same
property from the transitive closure of link libraries of the target.

Previously we computed this by constructing a generator expression
string like `$<TARGET_PROPERTY:lib,INTERFACE_COMPILE_DEFINITIONS>` and
recursively evaluating it with the generator expression engine.  Avoid
the string construction and parsing by creating and using a dedicated
evaluation method `cmGeneratorTarget::EvaluateInterfaceProperty` that
looks up the properties directly.

Issue: #18964, #18965

3 files changed, 95 insertions, 22 deletions

diff --git a/Source/cmGeneratorExpressionNode.cxx b/Source/cmGeneratorExpressionNode.cxx
index b268ea2..8d02b68 100644
--- a/Source/cmGeneratorExpressionNode.cxx
+++ b/Source/cmGeneratorExpressionNode.cxx
@@ -1243,6 +1243,11 @@ static const struct TargetPropertyNode : public cmGeneratorExpressionNode
       }
     }
 
+    if (isInterfaceProperty) {
+      return target->EvaluateInterfaceProperty(propertyName, context,
+                                               dagCheckerParent);
+    }
+
     cmGeneratorExpressionDAGChecker dagChecker(
       context->Backtrace, target, propertyName, content, dagCheckerParent);
 
@@ -1254,10 +1259,8 @@ static const struct TargetPropertyNode : public cmGeneratorExpressionNode
         // No error. We just skip cyclic references.
         return std::string();
       case cmGeneratorExpressionDAGChecker::ALREADY_SEEN:
-        if (isInterfaceProperty) {
-          // No error. We're not going to find anything new here.
-          return std::string();
-        }
+        // We handle transitive properties above.  For non-transitive
+        // properties we accept repeats anyway.
       case cmGeneratorExpressionDAGChecker::DAG:
         break;
     }
@@ -1328,27 +1331,15 @@ static const struct TargetPropertyNode : public cmGeneratorExpressionNode
     }
 
     if (!interfacePropertyName.empty()) {
-      cmGeneratorTarget const* headTarget =
-        context->HeadTarget && isInterfaceProperty ? context->HeadTarget
-                                                   : target;
+      cmGeneratorTarget const* headTarget = target;
       result = this->EvaluateDependentExpression(
         result, context->LG, context, headTarget, target, &dagChecker);
       std::string linkedTargetsContent;
-      if (isInterfaceProperty) {
-        if (cmLinkInterfaceLibraries const* iface =
-              target->GetLinkInterfaceLibraries(context->Config, headTarget,
-                                                true)) {
-          linkedTargetsContent = getLinkedTargetsContent(
-            iface->Libraries, target, headTarget, context, &dagChecker,
-            interfacePropertyName);
-        }
-      } else {
-        if (cmLinkImplementationLibraries const* impl =
-              target->GetLinkImplementationLibraries(context->Config)) {
-          linkedTargetsContent =
-            getLinkedTargetsContent(impl->Libraries, target, target, context,
-                                    &dagChecker, interfacePropertyName);
-        }
+      if (cmLinkImplementationLibraries const* impl =
+            target->GetLinkImplementationLibraries(context->Config)) {
+        linkedTargetsContent =
+          getLinkedTargetsContent(impl->Libraries, target, target, context,
+                                  &dagChecker, interfacePropertyName);
       }
       if (!linkedTargetsContent.empty()) {
         result += (result.empty() ? "" : ";") + linkedTargetsContent;
diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index 6e6c917..21da2fd 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -22,7 +22,9 @@
 #include "cmCustomCommandGenerator.h"
 #include "cmCustomCommandLines.h"
 #include "cmGeneratorExpression.h"
+#include "cmGeneratorExpressionContext.h"
 #include "cmGeneratorExpressionDAGChecker.h"
+#include "cmGeneratorExpressionNode.h"
 #include "cmGlobalGenerator.h"
 #include "cmLocalGenerator.h"
 #include "cmMakefile.h"
@@ -1141,6 +1143,79 @@ bool cmGeneratorTarget::GetPropertyAsBool(const std::string& prop) const
   return this->Target->GetPropertyAsBool(prop);
 }
 
+std::string cmGeneratorTarget::EvaluateInterfaceProperty(
+  std::string const& prop, cmGeneratorExpressionContext* context,
+  cmGeneratorExpressionDAGChecker* dagCheckerParent) const
+{
+  std::string result;
+
+  // Evaluate $<TARGET_PROPERTY:this,prop> as if it were compiled.  This is
+  // a subset of TargetPropertyNode::Evaluate without stringify/parse steps
+  // but sufficient for transitive interface properties.
+  cmGeneratorExpressionDAGChecker dagChecker(context->Backtrace, this, prop,
+                                             nullptr, dagCheckerParent);
+  switch (dagChecker.Check()) {
+    case cmGeneratorExpressionDAGChecker::SELF_REFERENCE:
+      dagChecker.ReportError(
+        context, "$<TARGET_PROPERTY:" + this->GetName() + "," + prop + ">");
+      return result;
+    case cmGeneratorExpressionDAGChecker::CYCLIC_REFERENCE:
+      // No error. We just skip cyclic references.
+      return result;
+    case cmGeneratorExpressionDAGChecker::ALREADY_SEEN:
+      // No error. We have already seen this transitive property.
+      return result;
+    case cmGeneratorExpressionDAGChecker::DAG:
+      break;
+  }
+
+  cmGeneratorTarget const* headTarget =
+    context->HeadTarget ? context->HeadTarget : this;
+
+  if (const char* p = this->GetProperty(prop)) {
+    result = cmGeneratorExpressionNode::EvaluateDependentExpression(
+      p, context->LG, context, headTarget, this, &dagChecker);
+  }
+
+  if (cmLinkInterfaceLibraries const* iface =
+        this->GetLinkInterfaceLibraries(context->Config, headTarget, true)) {
+    for (cmLinkItem const& lib : iface->Libraries) {
+      // Broken code can have a target in its own link interface.
+      // Don't follow such link interface entries so as not to create a
+      // self-referencing loop.
+      if (lib.Target && lib.Target != this) {
+        // Pretend $<TARGET_PROPERTY:lib.Target,prop> appeared in the
+        // above property and hand-evaluate it as if it were compiled.
+        // Create a context as cmCompiledGeneratorExpression::Evaluate does.
+        cmGeneratorExpressionContext libContext(
+          context->LG, context->Config, context->Quiet, headTarget, this,
+          context->EvaluateForBuildsystem, context->Backtrace,
+          context->Language);
+        std::string libResult = cmGeneratorExpression::StripEmptyListElements(
+          lib.Target->EvaluateInterfaceProperty(prop, &libContext,
+                                                &dagChecker));
+        if (!libResult.empty()) {
+          if (result.empty()) {
+            result = std::move(libResult);
+          } else {
+            result.reserve(result.size() + 1 + libResult.size());
+            result += ";";
+            result += libResult;
+          }
+        }
+        context->HadContextSensitiveCondition =
+          context->HadContextSensitiveCondition ||
+          libContext.HadContextSensitiveCondition;
+        context->HadHeadSensitiveCondition =
+          context->HadHeadSensitiveCondition ||
+          libContext.HadHeadSensitiveCondition;
+      }
+    }
+  }
+
+  return result;
+}
+
 namespace {
 void AddInterfaceEntries(cmGeneratorTarget const* headTarget,
                          std::string const& config, std::string const& prop,
diff --git a/Source/cmGeneratorTarget.h b/Source/cmGeneratorTarget.h
index e86535d..b875c40 100644
--- a/Source/cmGeneratorTarget.h
+++ b/Source/cmGeneratorTarget.h
@@ -25,6 +25,9 @@ class cmMakefile;
 class cmSourceFile;
 class cmTarget;
 
+struct cmGeneratorExpressionContext;
+struct cmGeneratorExpressionDAGChecker;
+
 class cmGeneratorTarget
 {
 public:
@@ -674,6 +677,10 @@ public:
 
   class TargetPropertyEntry;
 
+  std::string EvaluateInterfaceProperty(
+    std::string const& prop, cmGeneratorExpressionContext* context,
+    cmGeneratorExpressionDAGChecker* dagCheckerParent) const;
+
   bool HaveInstallTreeRPATH(const std::string& config) const;
 
   bool GetBuildRPATH(const std::string& config, std::string& rpath) const;