Ignore llvm.fake.use (#3264)

There's no SPIRV translation for `llvm.fake.use`, and currently it's
causing the translator to crash, so just ignore it to prevent crashes.

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@daada5684da36fd

Author: maarquitos14

llvm-spirv/lib/SPIRV/SPIRVWriter.cpp

@@ -3996,6 +3996,7 @@ bool LLVMToSPIRVBase::isKnownIntrinsic(Intrinsic::ID Id) {
   case Intrinsic::masked_gather:
   case Intrinsic::masked_scatter:
   case Intrinsic::modf:
+  case Intrinsic::fake_use:
     return true;
   default:
     // Unknown intrinsics' declarations should always be translated
@@ -4984,6 +4985,8 @@ SPIRVValue *LLVMToSPIRVBase::transIntrinsicInst(IntrinsicInst *II,
   case Intrinsic::trap:
   case Intrinsic::ubsantrap:
   case Intrinsic::debugtrap:
+  // Just ignore llvm.fake.use intrinsic, as it has no translation in SPIRV.
+  case Intrinsic::fake_use:
   // llvm.instrprof.* intrinsics are not supported
   case Intrinsic::instrprof_increment:
   case Intrinsic::instrprof_increment_step:

llvm-spirv/test/llvm-intrinsics/fake_use.ll

@@ -0,0 +1,20 @@
+; RUN: llvm-as %s -o %t.bc
+; RUN: llvm-spirv %t.bc -spirv-text -o %t
+; RUN: FileCheck < %t %s
+; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: spirv-val %t.spv
+target datalayout = "e-p:32:32-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024"
+target triple = "spir-unknown-unknown"
+
+; Function Attrs: nounwind
+; CHECK: Capability Addresses
+; CHECK: "foo"
+
+; Function Attrs: nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite)
+declare void @llvm.fake.use(...)
+
+define spir_kernel void @foo(ptr addrspace(1) %a) {
+entry:
+  call void (...) @llvm.fake.use(i8 undef)
+  ret void
+}