[SYCL] Create an empty integration header file with -fsycl-int-header (#3213)

When -save-temps is specified on the command-line, the Driver assumes
that an integration header file gets generated and includes the file
for consumption by subsequent phases.  However, currently the file
only gets created when there is something to emit inside it.  This
causes missing include file failures when a later compilation phase
expects this integration header file.

Signed-off-by: Premanand M Rao <[email protected]>

Author: premanandrao

clang/lib/Frontend/CompilerInvocation.cpp

@@ -2894,9 +2894,25 @@ bool CompilerInvocation::CreateFromArgs(CompilerInvocation &Res,
   if (LangOpts.OpenMPIsDevice)
     Res.getTargetOpts().HostTriple = Res.getFrontendOpts().AuxTriple;
 
-  // Set the triple of the host for SYCL device compile.
-  if (LangOpts.SYCLIsDevice)
+  if (LangOpts.SYCLIsDevice) {
+    // Set the triple of the host for SYCL device compile.
     Res.getTargetOpts().HostTriple = Res.getFrontendOpts().AuxTriple;
+    // If specified, create an empty integration header file for now.
+    const StringRef &HeaderName = LangOpts.SYCLIntHeader;
+    if (!HeaderName.empty()) {
+      Expected<llvm::sys::fs::file_t> ft =
+          llvm::sys::fs::openNativeFileForWrite(
+              HeaderName, llvm::sys::fs::CD_OpenAlways, llvm::sys::fs::OF_None);
+      if (ft)
+        llvm::sys::fs::closeFile(*ft);
+      else {
+        // Emit a message but don't terminate; compilation will fail
+        // later if this file is absent.
+        llvm::errs() << "Error: " << llvm::toString(ft.takeError())
+                     << " when opening " << HeaderName << "\n";
+      }
+    }
+  }
 
   Success &= ParseCodeGenArgs(Res.getCodeGenOpts(), Args, DashX, Diags, T,
                               Res.getFrontendOpts().OutputFile, LangOpts);

clang/test/SemaSYCL/sycl-empty-header.cpp

@@ -0,0 +1,12 @@
+// Test that at least an empty integration header file is created when
+// compiling source files with no device sycl construct.
+
+// RUN: mkdir -p %t_dir
+// RUN: %clang_cc1 -fsycl -fsycl-is-device -fsycl-int-header=%t.h -save-temps=cwd %s
+// RUN: ls %t.h
+// RUN: rm -f %t.h
+// RUN: touch %t.fail.h
+// RUN: chmod 400 %t.fail.h
+// RUN: %clang_cc1 -fsycl -fsycl-is-device -fsycl-int-header=%t.fail.h %s 2>&1 | FileCheck %s --check-prefix=SYCL-BADFILE
+// RUN: rm -f %t.fail.h
+// SYCL-BADFILE: Error: {{[Pp]ermission}} denied when opening {{.*.fail.h}}