[clang] [Driver][SYCL][Windows] Add SYCL windows runtime library linking support for SYCL JIT compilations (PR #194744)

[Michael Toguchi via cfe-commits]

================
@@ -85,6 +85,104 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
       CmdArgs.push_back(Args.MakeArgString("--dependent-lib=amath"));
   }
 
+  // ==========================================================================
+  // SYCL: Auto-add /MD if no C++ runtime specified
+  // SYCL requires dynamic C++ runtime because STL objects cross DLL boundaries
+  // This must happen BEFORE other CRT handling logic
+  // ==========================================================================
+  if (Args.hasFlag(options::OPT_fsycl, options::OPT_fno_sycl, false) &&
+      !Args.hasArg(options::OPT_nolibsycl) &&
+      !Args.hasArg(options::OPT_nostdlib) &&
+      !Args.hasArg(options::OPT_nostartfiles)) {
+
+    bool HasExplicitCRT = false;
+
+    // Check if user already specified a CRT flag
+    if (Args.hasArg(options::OPT__SLASH_MT) ||
+        Args.hasArg(options::OPT__SLASH_MTd) ||
+        Args.hasArg(options::OPT__SLASH_MD) ||
+        Args.hasArg(options::OPT__SLASH_MDd) ||
+        Args.hasArg(options::OPT_fms_runtime_lib_EQ))
+      HasExplicitCRT = true;
+
+    // Auto-add /MD if no CRT specified (makes dynamic CRT the default for SYCL)
+    if (!HasExplicitCRT) {
+      CmdArgs.push_back("/MD");
+    }
+  }
+
+  // ==========================================================================
+  // SYCL: Validate CRT compatibility and add SYCL runtime libraries
+  // This needs to run for both CL mode and regular mode
+  // ==========================================================================
+  if (Args.hasFlag(options::OPT_fsycl, options::OPT_fno_sycl, false) &&
+      !Args.hasArg(options::OPT_nolibsycl) &&
+      !Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles)) {
+
+    // ------------------------------------------------------------------------
+    // STEP 1: Validate that static CRT is not being used
+    // ------------------------------------------------------------------------
+    bool HasStaticCRT = false;
+
+    // Check for explicit /MT or /MTd flags
+    if (Args.hasArg(options::OPT__SLASH_MT) ||
+        Args.hasArg(options::OPT__SLASH_MTd)) {
+      HasStaticCRT = true;
+    }
+
+    // Check -fms-runtime-lib flag
+    if (const Arg *A = Args.getLastArg(options::OPT_fms_runtime_lib_EQ)) {
+      StringRef RuntimeLib = A->getValue();
+      if (RuntimeLib == "static" || RuntimeLib == "static_dbg") {
+        HasStaticCRT = true;
+      }
+    }
+
+    // Reject static CRT with SYCL
+    if (HasStaticCRT) {
+      TC.getDriver().Diag(diag::err_drv_sycl_requires_dynamic_crt);
+      // Continue to show other potential errors, but skip SYCL library linking
+    } else {
+      // ----------------------------------------------------------------------
+      // STEP 2: Add SYCL library search path
+      // ----------------------------------------------------------------------
+      CmdArgs.push_back(Args.MakeArgString(std::string("-libpath:") +
+                                           TC.getDriver().Dir + "/../lib"));
+
+      // ----------------------------------------------------------------------
+      // STEP 3: Determine if this is a debug build
+      // Only check DYNAMIC CRT flags (/MDd), never static (/MTd)
+      // ----------------------------------------------------------------------
+      bool IsDebugBuild = false;
+
+      // Method 1: Check -fms-runtime-lib=dll_dbg
+      if (const Arg *A = Args.getLastArg(options::OPT_fms_runtime_lib_EQ)) {
+        StringRef RuntimeVal = A->getValue();
+        if (RuntimeVal == "dll_dbg")
+          IsDebugBuild = true;
+      }
+
+      // Method 2: Check for /MDd flag (dynamic debug CRT)
+      if (Args.hasArg(options::OPT__SLASH_MDd))
+        IsDebugBuild = true;
+
+      // ----------------------------------------------------------------------
+      // STEP 4: Add appropriate SYCL runtime library
+      // Using LLVMSYCL for LLVM naming convention
+      // ----------------------------------------------------------------------
----------------
mdtoguchi wrote:

all the callouts of the 'steps' and the additional `----` borders on the comments are a bit out of place.  Just general comments of what is going on should be sufficent.

https://github.com/llvm/llvm-project/pull/194744