[SYCL] Remove noreturn function attribute

This is a follow-up to:
74aa9a0 [SYCL] Remove "unreachable" instruction from LLVM IR for SYCL
devices (#1789)

Noreturn function attribute gives LLVM optimization passes an
opportunity to re-structure code and insert an unreachable
instruction.

This happens when optimizations are turned on by
-fsycl-enable-optimizations, so noreturn function attribute must be
removed.

Signed-off-by: Andrew Savonichev <[email protected]>

Author: Andrew Savonichev

clang/lib/CodeGen/CGCall.cpp

@@ -4971,10 +4971,21 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
 
   // 4. Finish the call.
 
+  // SYCL does not support C++ exceptions or termination in device code, so all
+  // functions have to return.
+  bool SyclSkipNoReturn = false;
+  if (getLangOpts().SYCLIsDevice && CI->doesNotReturn()) {
+    if (auto *F = CI->getCalledFunction())
+      F->removeFnAttr(llvm::Attribute::NoReturn);
+    CI->removeAttribute(llvm::AttributeList::FunctionIndex,
+                        llvm::Attribute::NoReturn);
+    SyclSkipNoReturn = true;
+  }
+
   // If the call doesn't return for non-sycl devices, finish the basic block and
   // clear the insertion point; this allows the rest of IRGen to discard
   // unreachable code.
-  if (CI->doesNotReturn() && !getLangOpts().SYCLIsDevice) {
+  if (!SyclSkipNoReturn && CI->doesNotReturn()) {
     if (UnusedReturnSizePtr)
       PopCleanupBlock();
 

clang/test/CodeGenSYCL/remove-ur-inst.cpp

@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsycl -fsycl-is-device -triple spir64-unknown-unknown-sycldevice -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -fsycl -fsycl-is-device -fsycl-enable-optimizations -triple spir64-unknown-unknown-sycldevice -emit-llvm %s -o - | FileCheck %s
 
 SYCL_EXTERNAL void doesNotReturn() throw() __attribute__((__noreturn__));
 
@@ -11,6 +12,7 @@ int main() {
   kernel<class test>([]() {
     doesNotReturn();
     // CHECK-NOT: unreachable
+    // CHECK-NOT: noreturn
   });
   return 0;
-}
+}