[SYCL] Add experimental flag to enable front-end optimizations (#1376)

NOTE: This flag is not exposed to the driver and not intended for users.
It's added to make experiments and identify issues with optimizations.

Signed-off-by: Alexey Bader <alexey.bader@intel.com>

Author: bader

clang/include/clang/Driver/CC1Options.td

@@ -919,6 +919,8 @@ def fsycl_std_layout_kernel_params: Flag<["-"], "fsycl-std-layout-kernel-params"
 def fsycl_allow_func_ptr : Flag<["-"], "fsycl-allow-func-ptr">,
   HelpText<"Allow function pointers in SYCL device.">;
 def fno_sycl_allow_func_ptr : Flag<["-"], "fno-sycl-allow-func-ptr">;
+def fsycl_enable_optimizations: Flag<["-"], "fsycl-enable-optimizations">,
+  HelpText<"Experimental flag enabling standard optimization in the front-end.">;
 
 } // let Flags = [CC1Option]
 

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4109,10 +4109,6 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
       }
     }
 
-    if (Triple.isSPIR()) {
-      CmdArgs.push_back("-disable-llvm-passes");
-    }
-
     if (Args.hasFlag(options::OPT_fsycl_allow_func_ptr,
                      options::OPT_fno_sycl_allow_func_ptr, false)) {
       CmdArgs.push_back("-fsycl-allow-func-ptr");

clang/lib/Frontend/CompilerInvocation.cpp

@@ -780,7 +780,10 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
           Args.getLastArg(OPT_emit_llvm_uselists, OPT_no_emit_llvm_uselists))
     Opts.EmitLLVMUseLists = A->getOption().getID() == OPT_emit_llvm_uselists;
 
-  Opts.DisableLLVMPasses = Args.hasArg(OPT_disable_llvm_passes);
+  Opts.DisableLLVMPasses =
+      Args.hasArg(OPT_disable_llvm_passes) ||
+      (Args.hasArg(OPT_fsycl_is_device) && Triple.isSPIR() &&
+       !Args.hasArg(OPT_fsycl_enable_optimizations));
   Opts.DisableLifetimeMarkers = Args.hasArg(OPT_disable_lifetimemarkers);
 
   const llvm::Triple::ArchType DebugEntryValueArchs[] = {

clang/test/CodeGenSYCL/inline_asm.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsycl -fsycl-is-device -triple spir64-unknown-unknown-sycldevice -emit-llvm -x c++ %s -o - | FileCheck %s
+// RUN: %clang_cc1 -fsycl -fsycl-is-device -fsycl-enable-optimizations -triple spir64-unknown-unknown-sycldevice -emit-llvm -x c++ %s -o - | FileCheck %s
 
 class kernel;