[clang][deps] Set -disable-free for module compilations

The command-line arguments for module builds are cc1 commands, so they
do not implicitly set -disable-free like a driver invocation, and
Tooling will disable it for the scanning instance itself. Set
-disable-free explicitly so that separate invocations for building
modules will not pay for freeing memory unnecessarily.

Differential Revision: https://reviews.llvm.org/D127229

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

@@ -137,11 +137,11 @@ public:
   DependencyScanningAction(
       StringRef WorkingDirectory, DependencyConsumer &Consumer,
       llvm::IntrusiveRefCntPtr<DependencyScanningWorkerFilesystem> DepFS,
-      ScanningOutputFormat Format, bool OptimizeArgs,
+      ScanningOutputFormat Format, bool OptimizeArgs, bool DisableFree,
       llvm::Optional<StringRef> ModuleName = None)
       : WorkingDirectory(WorkingDirectory), Consumer(Consumer),
         DepFS(std::move(DepFS)), Format(Format), OptimizeArgs(OptimizeArgs),
-        ModuleName(ModuleName) {}
+        DisableFree(DisableFree), ModuleName(ModuleName) {}
 
   bool runInvocation(std::shared_ptr<CompilerInvocation> Invocation,
                      FileManager *FileMgr,
@@ -149,6 +149,8 @@ public:
                      DiagnosticConsumer *DiagConsumer) override {
     // Make a deep copy of the original Clang invocation.
     CompilerInvocation OriginalInvocation(*Invocation);
+    // Restore the value of DisableFree, which may be modified by Tooling.
+    OriginalInvocation.getFrontendOpts().DisableFree = DisableFree;
 
     // Create a compiler instance to handle the actual work.
     CompilerInstance ScanInstance(std::move(PCHContainerOps));
@@ -255,6 +257,7 @@ private:
   llvm::IntrusiveRefCntPtr<DependencyScanningWorkerFilesystem> DepFS;
   ScanningOutputFormat Format;
   bool OptimizeArgs;
+  bool DisableFree;
   llvm::Optional<StringRef> ModuleName;
 };
 
@@ -329,9 +332,13 @@ llvm::Error DependencyScanningWorker::computeDependencies(
 
   return runWithDiags(CreateAndPopulateDiagOpts(FinalCCommandLine).release(),
                       [&](DiagnosticConsumer &DC, DiagnosticOptions &DiagOpts) {
+                        // DisableFree is modified by Tooling for running
+                        // in-process; preserve the original value, which is
+                        // always true for a driver invocation.
+                        bool DisableFree = true;
                         DependencyScanningAction Action(
                             WorkingDirectory, Consumer, DepFS, Format,
-                            OptimizeArgs, ModuleName);
+                            OptimizeArgs, DisableFree, ModuleName);
                         // Create an invocation that uses the underlying file
                         // system to ensure that any file system requests that
                         // are made by the driver do not go through the

clang/test/ClangScanDeps/modules-disable-free.c

@@ -0,0 +1,34 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s|DIR|%/t|g" %t/compile-commands.json.in > %t/compile-commands.json
+
+// RUN: clang-scan-deps -compilation-database %t/compile-commands.json -j 1 -format experimental-full \
+// RUN:   -mode preprocess-dependency-directives -generate-modules-path-args > %t/output
+// RUN: FileCheck %s < %t/output
+
+// CHECK: "-disable-free",
+
+//--- compile-commands.json.in
+
+[{
+  "directory": "DIR",
+  "command": "clang -c DIR/main.c -fmodules -fmodules-cache-path=DIR/module-cache -fimplicit-modules -fimplicit-module-maps",
+  "file": "DIR/main.c"
+}]
+
+//--- module.modulemap
+
+module A {
+  header "a.h"
+}
+
+//--- a.h
+
+void a(void);
+
+//--- main.c
+
+#include "a.h"
+void m() {
+  a();
+}