[SYCL] Disable vectorizers in early optimizations (#2402)

Author: AlexeySachkov

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5995,10 +5995,17 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                     options::OPT_fno_gnu_inline_asm, true))
     CmdArgs.push_back("-fno-gnu-inline-asm");
 
+  bool EnableSYCLEarlyOptimizations =
+      Args.hasFlag(options::OPT_fsycl_early_optimizations,
+                   options::OPT_fno_sycl_early_optimizations,
+                   Triple.getSubArch() != llvm::Triple::SPIRSubArch_fpga);
+
   // Enable vectorization per default according to the optimization level
   // selected. For optimization levels that want vectorization we use the alias
   // option to simplify the hasFlag logic.
   bool EnableVec = shouldEnableVectorizerAtOLevel(Args, false);
+  if (UseSYCLTriple && EnableSYCLEarlyOptimizations)
+    EnableVec = false; // But disable vectorization for SYCL device code
   OptSpecifier VectorizeAliasOption =
       EnableVec ? options::OPT_O_Group : options::OPT_fvectorize;
   if (Args.hasFlag(options::OPT_fvectorize, VectorizeAliasOption,
@@ -6007,6 +6014,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   // -fslp-vectorize is enabled based on the optimization level selected.
   bool EnableSLPVec = shouldEnableVectorizerAtOLevel(Args, true);
+  if (UseSYCLTriple && EnableSYCLEarlyOptimizations)
+    EnableSLPVec = false; // But disable vectorization for SYCL device code
   OptSpecifier SLPVectAliasOption =
       EnableSLPVec ? options::OPT_O_Group : options::OPT_fslp_vectorize;
   if (Args.hasFlag(options::OPT_fslp_vectorize, SLPVectAliasOption,

clang/test/Driver/sycl-device-optimizations.cpp

@@ -36,3 +36,13 @@
 // RUN:   | FileCheck -check-prefix=CHECK-DAE %s
 // CHECK-DAE: clang{{.*}} "-fenable-sycl-dae"
 // CHECK-DAE: sycl-post-link{{.*}} "-emit-param-info"
+
+/// Check that vectorizers are disabled by default:
+// RUN:   %clang -### -fsycl %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-VEC-DEFAULT %s
+// CHECK-VEC-DEFAULT-NOT: clang{{.*}} "-fsycl-is-device"{{.*}} "-vectorize-loops"
+// CHECK-VEC-DEFAULT-NOT: clang{{.*}} "-fsycl-is-device"{{.*}} "-vectorize-slp"
+/// Check that vectorizers can still be enabled manually:
+// RUN:   %clang -### -fsycl -fvectorize -fslp-vectorize %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-VEC-ENABLE %s
+// CHECK-VEC-ENABLE: clang{{.*}} "-fsycl-is-device"{{.*}}"-vectorize-loops"{{.*}}"-vectorize-slp"