[SYCL] Disable inlining kernel lambda operator at -O0 (#7578)

PR #6977 enabled always inlining kernel lambda operators.
This PR disables this at -O0 as it was leading to a poor
debugging experience.

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5097,8 +5097,14 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
       CmdArgs.push_back("-sycl-std=2020");
     }
 
+    bool DisableSYCLForceInlineKernelLambda = false;
+    if (Arg *A = Args.getLastArg(options::OPT_O_Group))
+      DisableSYCLForceInlineKernelLambda =
+          A->getOption().matches(options::OPT_O0);
+    // At -O0, disable the inlining for debugging purposes.
     if (!Args.hasFlag(options::OPT_fsycl_force_inline_kernel_lambda,
-                      options::OPT_fno_sycl_force_inline_kernel_lambda, true))
+                      options::OPT_fno_sycl_force_inline_kernel_lambda,
+                      !DisableSYCLForceInlineKernelLambda))
       CmdArgs.push_back("-fno-sycl-force-inline-kernel-lambda");
 
     if (!Args.hasFlag(options::OPT_fsycl_unnamed_lambda,

clang/test/Driver/sycl.c

@@ -75,7 +75,12 @@
 // -fsycl-force-inline-kernel-lambda
 // RUN: %clangxx -### -fsycl-device-only -fno-sycl-force-inline-kernel-lambda  %s 2>&1 | FileCheck %s --check-prefix=CHECK-NOT-INLINE
 // RUN: %clang_cl -### -fsycl-device-only -fno-sycl-force-inline-kernel-lambda  %s 2>&1 | FileCheck %s --check-prefix=CHECK-NOT-INLINE
+// RUN: %clangxx -### -fsycl-device-only -O0 %s 2>&1 | FileCheck %s --check-prefix=CHECK-NOT-INLINE
+// RUN: %clang_cl -### -fsycl-device-only -Od %s 2>&1 | FileCheck %s --check-prefix=CHECK-NOT-INLINE
+// RUN: %clangxx -### -fsycl-device-only -O1 %s 2>&1 | FileCheck %s --check-prefix=CHECK-INLINE
+// RUN: %clang_cl -### -fsycl-device-only -O2 %s 2>&1 | FileCheck %s --check-prefix=CHECK-INLINE
 // CHECK-NOT-INLINE: "-fno-sycl-force-inline-kernel-lambda"
+// CHECK-INLINE-NOT: "-fno-sycl-force-inline-kernel-lambda"
 
 /// -fsycl-device-only triple checks
 // RUN: %clang -fsycl-device-only -target x86_64-unknown-linux-gnu -### %s 2>&1 \

sycl/doc/UsersManual.md

@@ -112,7 +112,8 @@ and not recommended to use in production environment.
   Enables/Disables inlining of the kernel lambda operator into the compiler
   generated entry point function. This flag does not apply to ESIMD
   kernels.
-  Enabled by default.
+  Disabled when optimizations are disabled (-O0 or equivalent). Enabled
+  otherwise.
 
 **`-fgpu-inline-threshold=<n>`**