Translate LLVM-IR zero-length arrays to 1-length arrays in SPIR-V (#2743)

The LLVM-IR type of zero-length array does not seem to have a mapping into SPIR-V type, rather it outputs an error since the obvious choice of zero-length array is not valid in SPIR-V. This, for example, prohibits us from using unbounded arrays in SYCL device kernels because they are typically represented in LLVM-IR through zero-length arrays. This PR attempts to introduce a workaround to this by lowering a zero-length array in LLVM-IR to a 1-length array in SPIR-V.

Author: lbushi25

lib/SPIRV/SPIRVWriter.cpp

@@ -449,24 +449,19 @@ SPIRVType *LLVMToSPIRVBase::transType(Type *T) {
   if (T->isArrayTy()) {
     // SPIR-V 1.3 s3.32.6: Length is the number of elements in the array.
     //                     It must be at least 1.
-    if (T->getArrayNumElements() < 1) {
-      std::string Str;
-      llvm::raw_string_ostream OS(Str);
-      OS << *T;
-      SPIRVCK(T->getArrayNumElements() >= 1, InvalidArraySize, OS.str());
-    }
+    const auto ArraySize =
+        T->getArrayNumElements() ? T->getArrayNumElements() : 1;
     Type *ElTy = T->getArrayElementType();
     SPIRVType *TransType = BM->addArrayType(
         transType(ElTy),
         static_cast<SPIRVConstant *>(transValue(
-            ConstantInt::get(getSizetType(), T->getArrayNumElements(), false),
-            nullptr)));
+            ConstantInt::get(getSizetType(), ArraySize, false), nullptr)));
     mapType(T, TransType);
     if (ElTy->isPointerTy()) {
       mapType(
           ArrayType::get(TypedPointerType::get(Type::getInt8Ty(*Ctx),
                                                ElTy->getPointerAddressSpace()),
-                         T->getArrayNumElements()),
+                         ArraySize),
           TransType);
     }
     return TransType;

lib/SPIRV/libSPIRV/SPIRVErrorEnum.h

@@ -10,7 +10,6 @@ _SPIRV_OP(InvalidMemoryModel, "Expects 0-3.")
 _SPIRV_OP(InvalidFunctionControlMask, "")
 _SPIRV_OP(InvalidBuiltinSetName, "Expects OpenCL.std.")
 _SPIRV_OP(InvalidFunctionCall, "Unexpected llvm intrinsic:\n")
-_SPIRV_OP(InvalidArraySize, "Array size must be at least 1:")
 _SPIRV_OP(InvalidBitWidth, "Invalid bit width in input:")
 _SPIRV_OP(InvalidModule, "Invalid SPIR-V module:")
 _SPIRV_OP(InvalidLlvmModule, "Invalid LLVM module:")

test/negative/zero-length-array.ll renamed to test/zero-length-array.ll

@@ -1,7 +1,9 @@
 ; RUN: llvm-as %s -o %t.bc
-; RUN: not llvm-spirv %t.bc -o %t.spv 2>&1 | FileCheck %s
+; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: spirv-dis %t.spv | FileCheck %s
 
-; CHECK: InvalidArraySize: Array size must be at least 1: [0 x i32]
+; CHECK: [[REGISTER:%[a-zA-Z0-9_]+]] = OpConstant %uint 1
+; CHECK: OpTypeArray %uint [[REGISTER]]
 
 source_filename = "test.cl"
 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"