[clang] Infer compilation directory in driver

When building with -fdebug-compilation-dir/-fcoverige-compilation-dir,
infer the compilation directory in clang driver, rather than try to
fallback to VFS current working directory lookup during CodeGen. This
allows compilation directory to be used as it is passed via cc1 flag and
the value can be empty to remove dependency on CWD if needed.

Reviewers: adrian-prantl, dwblaikie

Reviewed By: adrian-prantl, dwblaikie

Pull Request: llvm#150112

Author: cachemeifyoucan

clang/lib/Driver/ToolChains/Clang.cpp

@@ -243,17 +243,19 @@ static bool ShouldEnableAutolink(const ArgList &Args, const ToolChain &TC,
 static const char *addDebugCompDirArg(const ArgList &Args,
                                       ArgStringList &CmdArgs,
                                       const llvm::vfs::FileSystem &VFS) {
+  std::string DebugCompDir;
   if (Arg *A = Args.getLastArg(options::OPT_ffile_compilation_dir_EQ,
-                               options::OPT_fdebug_compilation_dir_EQ)) {
-    if (A->getOption().matches(options::OPT_ffile_compilation_dir_EQ))
-      CmdArgs.push_back(Args.MakeArgString(Twine("-fdebug-compilation-dir=") +
-                                           A->getValue()));
+                               options::OPT_fdebug_compilation_dir_EQ))
+    DebugCompDir = A->getValue();
+
+  if (DebugCompDir.empty()) {
+    if (llvm::ErrorOr<std::string> CWD = VFS.getCurrentWorkingDirectory())
+      DebugCompDir = std::move(*CWD);
     else
-      A->render(Args, CmdArgs);
-  } else if (llvm::ErrorOr<std::string> CWD =
-                 VFS.getCurrentWorkingDirectory()) {
-    CmdArgs.push_back(Args.MakeArgString("-fdebug-compilation-dir=" + *CWD));
+      return nullptr;
   }
+  CmdArgs.push_back(
+      Args.MakeArgString("-fdebug-compilation-dir=" + DebugCompDir));
   StringRef Path(CmdArgs.back());
   return Path.substr(Path.find('=') + 1).data();
 }
@@ -542,17 +544,17 @@ static void addPGOAndCoverageFlags(const ToolChain &TC, Compilation &C,
     CmdArgs.push_back("-fcoverage-mcdc");
   }
 
+  StringRef CoverageCompDir;
   if (Arg *A = Args.getLastArg(options::OPT_ffile_compilation_dir_EQ,
-                               options::OPT_fcoverage_compilation_dir_EQ)) {
-    if (A->getOption().matches(options::OPT_ffile_compilation_dir_EQ))
-      CmdArgs.push_back(Args.MakeArgString(
-          Twine("-fcoverage-compilation-dir=") + A->getValue()));
-    else
-      A->render(Args, CmdArgs);
-  } else if (llvm::ErrorOr<std::string> CWD =
-                 D.getVFS().getCurrentWorkingDirectory()) {
-    CmdArgs.push_back(Args.MakeArgString("-fcoverage-compilation-dir=" + *CWD));
-  }
+                               options::OPT_fcoverage_compilation_dir_EQ))
+    CoverageCompDir = A->getValue();
+  if (CoverageCompDir.empty()) {
+    if (auto CWD = D.getVFS().getCurrentWorkingDirectory())
+      CmdArgs.push_back(
+          Args.MakeArgString(Twine("-fcoverage-compilation-dir=") + *CWD));
+  } else
+    CmdArgs.push_back(Args.MakeArgString(Twine("-fcoverage-compilation-dir=") +
+                                         CoverageCompDir));
 
   if (Args.hasArg(options::OPT_fprofile_exclude_files_EQ)) {
     auto *Arg = Args.getLastArg(options::OPT_fprofile_exclude_files_EQ);

clang/test/Driver/compilation-dir.c

@@ -8,3 +8,8 @@
 // RUN: %clang -### -integrated-as -ffile-compilation-dir=. -x assembler %s 2>&1 | FileCheck -check-prefixes=CHECK-DEBUG-COMPILATION-DIR %s
 // CHECK-DEBUG-COMPILATION-DIR: "-fdebug-compilation-dir=."
 // CHECK-DEBUG-COMPILATION-DIR-NOT: "-ffile-compilation-dir=."
+
+// RUN: %clang -### -S %s -working-directory %S 2>&1 | FileCheck -check-prefix=CHECK-CWD %s
+// RUN: cd %S
+// RUN: %clang -### -S %s 2>&1 | FileCheck -check-prefix=CHECK-CWD %s
+// CHECK-CWD: -fdebug-compilation-dir={{.*}}Driver