[SYCL][Fusion] Prevent deletion of original kernel function if inlining fails (intel#12153)

In the unlikely edge case that an original kernel function cannot be
inlined into the newly constructed fused kernel function, we have to
ensure that a) the original kernel function is not deleted from the
module, and b) is called with the correct calling convention and
attributes.

Signed-off-by: Julian Oppermann <julian.oppermann@codeplay.com>

Author: jopperm

sycl-fusion/passes/kernel-fusion/SYCLKernelFusion.cpp

@@ -254,6 +254,8 @@ static Expected<CallInst *> createFusionCall(
   // Insert call
   Builder.SetInsertPoint(IPs.CallInsertion);
   auto *Res = Builder.CreateCall(F, CallArgs);
+  Res->setCallingConv(F->getCallingConv());
+  Res->setAttributes(F->getAttributes());
   {
     // If we have introduced a guard, branch to barrier.
     auto *BrTarget = IPs.Exit;
@@ -586,11 +588,13 @@ Error SYCLKernelFusion::fuseKernel(
       // InlineFunction(...) will leave the program in a well-defined state
       // in case it fails, and calling the function is still semantically
       // correct, although it might hinder some optimizations across the borders
-      // of the fused functions.
-      FUSION_DEBUG(llvm::dbgs()
-                   << "WARNING: Inlining of "
-                   << InlineCall->getCalledFunction()->getName()
-                   << " failed due to: " << InlineRes.getFailureReason());
+      // of the fused functions. We need to prevent deletion of the called
+      // function, though.
+      auto *Callee = InlineCall->getCalledFunction();
+      FUSION_DEBUG(llvm::dbgs() << "WARNING: Inlining of " << Callee->getName()
+                                << " failed due to: "
+                                << InlineRes.getFailureReason() << '\n');
+      ToCleanUp.erase(Callee);
     }
   }