[SYCL] Disable dead arg elimination for free function kernels

llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp

@@ -575,6 +575,17 @@ void DeadArgumentEliminationPass::surveyFunction(const Function &F) {
     return;
   }
 
+  // Do not modify arguments when the SYCL kernel is a free function kernel.
+  // In this case, the user sets the arguments of the kernel by themselves
+  // and dead argument elimination may interfere with their expectations.
+  bool FuncIsSyclFreeFunctionKernel =
+      F.hasFnAttribute("sycl-single-task-kernel") ||
+      F.hasFnAttribute("sycl-nd-range-kernel");
+  if (FuncIsSyclFreeFunctionKernel) {
+    markFrozen(F);
+    return;
+  }
+
   LLVM_DEBUG(
       dbgs() << "DeadArgumentEliminationPass - Inspecting callers for fn: "
              << F.getName() << "\n");

llvm/test/Transforms/DeadArgElim/sycl-kernels-neg.ll

@@ -32,6 +32,32 @@ define weak_odr void @ESIMDKernel(float %arg1, float %arg2) !sycl_explicit_simd
   ret void
 }
 
+; The following two tests ensure that dead arguments are not eliminated
+; from a free function kernel.
+
+define weak_odr spir_kernel void @FreeFuncKernelSingleTask(float %arg1, float %arg2) "sycl-single-task-kernel"="0" {
+; CHECK-LABEL: define {{[^@]+}}@FreeFuncKernelSingleTask
+; CHECK-SAME: (float [[ARG1:%.*]], float [[ARG2:%.*]]) #[[SINGLE_TASK_ATTR]] {
+; CHECK-NEXT: call void @foo(float [[ARG1]])
+; CHECK-NEXT: ret void
+;
+  call void @foo(float %arg1)
+  ret void
+}
+
+define weak_odr spir_kernel void @FreeFuncKernelNdRange(float %arg1, float %arg2) "sycl-nd-range-kernel"="0" {
+; CHECK-LABEL: define {{[^@]+}}@FreeFuncKernelNdRange
+; CHECK-SAME: (float [[ARG1:%.*]], float [[ARG2:%.*]]) #[[ND_RANGE_ATTR:[0-9]]] {
+; CHECK-NEXT: call void @foo(float [[ARG1]])
+; CHECK-NEXT: ret void
+;
+  call void @foo(float %arg1)
+  ret void
+}
+
 declare void @foo(float %arg)
 
+; CHECK: attributes #[[SINGLE_TASK_ATTR]] = { "sycl-single-task-kernel"="0" }
+; CHECK: attributes #[[ND_RANGE_ATTR]] = { "sycl-nd-range-kernel"="0" }
+
 !0 = !{}