IPRA: Don't crash on null getCallPreservedMask

[arsenm]

Summary

Kernels aren't callable, so they don't have a call preserved mask.

[arsenm]

ping

[MatzeB]

LGTM

[arsenm]

r310172

lib/CodeGen/RegUsageInfoCollector.cpp

if (!MRI->def_empty(PReg)) {
       for (MCRegAliasIterator AI(PReg, TRI, true); AI.isValid(); ++AI)
         SetRegAsDefined(*AI);
     }
   }
 
   if (!TargetFrameLowering::isSafeForNoCSROpt(F)) {
     const uint32_t *CallPreservedMask =
         TRI->getCallPreservedMask(MF, F->getCallingConv());
+    if (CallPreservedMask) {
       // Set callee saved register as preserved.
       for (unsigned i = 0; i < RegMaskSize; ++i)
         RegMask[i] = RegMask[i] | CallPreservedMask[i];
+    }
   } else {
     ++NumCSROpt;
     DEBUG(dbgs() << MF.getName()
                  << " function optimized for not having CSR.\n");
   }
 
   for (unsigned PReg = 1, PRegE = TRI->getNumRegs(); PReg < PRegE; ++PReg)
     if (MachineOperand::clobbersPhysReg(&(RegMask[0]), PReg))
       DEBUG(dbgs() << TRI->getName(PReg) << " ");
 
   DEBUG(dbgs() << " \n----------------------------------------\n");
 
   PRUI->storeUpdateRegUsageInfo(F, std::move(RegMask));
 
   return false;
 }

test/CodeGen/AMDGPU/ipra.ll

+; RUN: llc -mtriple=amdgcn-amd-amdhsa -verify-machineinstrs -enable-ipra < %s | FileCheck -check-prefix=GCN %s
+
+; Kernels are not called, so there is no call preserved mask.
+; GCN-LABEL: {{^}}kernel:
+; GCN: flat_store_dword
+define amdgpu_kernel void @kernel(i32 addrspace(1)* %out) #0 {
+entry:
+  store i32 0, i32 addrspace(1)* %out
+  ret void
+}
+
+attributes #0 = { nounwind }