AMDGPU: Fix crashing on kernel declarations when lowering LDS

[arsenm]

Summary

This was trying to insert the used marker into a declaration.

[arsenm]

ce51c5d4a935cb1a4b99e5c95e0c4c5724b64375

llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp

   }
 
   bool runOnModule(Module &M) override {
     UsedList = AMDGPU::getUsedList(M);
 
     bool Changed = processUsedLDS(M);
 
     for (Function &F : M.functions()) {
+      if (F.isDeclaration())
+        continue;
+
       // Only lower compute kernels' LDS.
       if (!AMDGPU::isKernel(F.getCallingConv()))
         continue;
       Changed |= processUsedLDS(M, &F);
     }
 
     UsedList.clear();
     return Changed;

 
     // Mark kernels with asm that reads the address of the allocated structure
     // This is not necessary for lowering. This lets other passes, specifically
     // PromoteAlloca, accurately calculate how much LDS will be used by the
     // kernel after lowering.
     if (!F) {
       IRBuilder<> Builder(Ctx);
       SmallPtrSet<Function *, 32> Kernels;
-      for (auto &I : M.functions()) {
-        Function *Func = &I;
-        if (AMDGPU::isKernelCC(Func) && !Kernels.contains(Func)) {
-          markUsedByKernel(Builder, Func, SGV);
-          Kernels.insert(Func);
+      for (Function &Func : M.functions()) {
+        if (Func.isDeclaration())
+          continue;
+
+        if (AMDGPU::isKernelCC(&Func) && !Kernels.contains(&Func)) {
+          markUsedByKernel(Builder, &Func, SGV);
+          Kernels.insert(&Func);
         }
       }
     }
     return true;
   }
 
   void refineUsesAlignmentAndAA(Value *Ptr, Align A, const DataLayout &DL,
                                 MDNode *AliasScope, MDNode *NoAlias,

llvm/test/CodeGen/AMDGPU/lower-module-lds.ll

 }
 
 ; This kernel does not need to alloc the LDS block as it makes no calls
 ; CHECK-LABEL: @kern_empty()
 ; CHECK: call void @llvm.donothing() [ "ExplicitUse"(%llvm.amdgcn.module.lds.t addrspace(3)* @llvm.amdgcn.module.lds) ]
 define spir_kernel void @kern_empty() {
   ret void
 }
+
+; Make sure we don't crash trying to insert code into a kernel
+; declaration.
+declare amdgpu_kernel void @kernel_declaration()