Skip function declarations in the SLM resolution pass

Function declarations have no basic blocks and instructions, so they
should be skipped in the SLM resolution pass.

(cherry picked from commit 3db59df)

Author: vmustya

IGC/VectorCompiler/lib/GenXCodeGen/GenXSLMResolution.cpp

@@ -279,9 +279,12 @@ bool GenXSLMResolution::runOnModule(Module &M) {
 
   auto SLMVars = collectSLMVariables(M);
   if (!SLMVars.empty())
-    for (auto &F : M.functions())
+    for (auto &F : M.functions()) {
+      if (F.isDeclaration())
+        continue;
       Modified |=
           vc::breakConstantExprs(&F, vc::LegalizationStage::NotLegalized);
+    }
 
   for (auto &F : M.functions())
     if (vc::isKernel(&F))

IGC/VectorCompiler/test/GenXSLMResolution/simple.ll

@@ -30,13 +30,20 @@ define dllexport spir_kernel void @kernel() #0 {
   ; CHECK-OPAQUE-PTRS: %load_struct_i64i8 = load { i64, i8 }, ptr addrspace(3) inttoptr (i32 8 to ptr addrspace(3))
   %load_struct_i64i8 = load { i64, i8 }, { i64, i8 } addrspace(3)* @slm_struct_i64i8
 
+  ; CHECK-TYPED-PTRS: call void @llvm.genx.barrier()
+  ; CHECK-OPAQUE-PTRS: call void @llvm.genx.barrier()
+  call void @llvm.genx.barrier()
+
   ; CHECK-TYPED-PTRS: %load_struct_align = load { i1 }, { i1 } addrspace(3)* inttoptr (i32 268435456 to { i1 } addrspace(3)*)
   ; CHECK-OPAQUE-PTRS: %load_struct_align = load { i1 }, ptr addrspace(3) inttoptr (i32 268435456 to ptr addrspace(3))
   %load_struct_align = load { i1 }, { i1 } addrspace(3)* @slm_struct_align
   ret void
 }
 
+declare void @llvm.genx.barrier() #1
+
 attributes #0 = { noinline nounwind "CMGenxMain" }
+attributes #1 = { nounwind convergent }
 
 !genx.kernels = !{!0}
 !genx.kernel.internal = !{!3}