[SPIR-V] Improve how lowering of formal arguments in SPIR-V Backend interprets a value of 'kernel_arg_type' (#78730)

The goal of this PR is to tolerate differences between description of
formal arguments by function metadata (represented by "kernel_arg_type")
and LLVM actual parameter types. A compiler may use "kernel_arg_type" of
function metadata fields to encode detailed type information, whereas
LLVM IR may utilize for an actual parameter a more general type, in
particular, opaque pointer type. This PR proposes to resolve this by a
fallback to LLVM actual parameter types during the lowering of formal
function arguments in cases when the type can't be created by string
content of "kernel_arg_type", i.e., when "kernel_arg_type" contains a
type unknown for the SPIR-V Backend.

An example of the issue manifestation is
https://github.com/KhronosGroup/SPIRV-LLVM-Translator/blob/main/test/transcoding/KernelArgTypeInOpString.ll,
where a compiler generates for the following kernel function detailed
`kernel_arg_type` info in a form of `!{!"image_kernel_data*", !"myInt",
!"struct struct_name*"}`, and in LLVM IR same arguments are referred to
as `@foo(ptr addrspace(1) %in, i32 %out, ptr addrspace(1) %outData)`.
Both definitions are correct, and the resulting LLVM IR is correct, but
lowering stage of SPIR-V Backend fails to generate SPIR-V type.

```
typedef int myInt;

 typedef struct {
   int width;
   int height;
 } image_kernel_data;

 struct struct_name {
   int i;
   int y;
 };
 void kernel foo(__global image_kernel_data* in,
                 __global struct struct_name *outData,
                 myInt out) {}
```

```
define spir_kernel void @foo(ptr addrspace(1) %in, i32 %out, ptr addrspace(1) %outData) ... !kernel_arg_type !7 ... {
entry:
  ret void
}
...
!7 = !{!"image_kernel_data*", !"myInt", !"struct struct_name*"}
```

The PR changes a contract of `SPIRVType *getArgSPIRVType(...)` in a way
that it may return `nullptr` to signal that the metadata string content
is not recognized, so corresponding comments are added and a couple of
checks for `nullptr` are inserted where appropriate.

Author: VyacheslavLevytskyy

llvm/lib/Target/SPIRV/SPIRVBuiltins.cpp

@@ -1386,6 +1386,11 @@ static bool generateSampleImageInst(const StringRef DemangledCall,
       ReturnType = ReturnType.substr(0, ReturnType.find('('));
     }
     SPIRVType *Type = GR->getOrCreateSPIRVTypeByName(ReturnType, MIRBuilder);
+    if (!Type) {
+      std::string DiagMsg =
+          "Unable to recognize SPIRV type name: " + ReturnType;
+      report_fatal_error(DiagMsg.c_str());
+    }
     MRI->setRegClass(Call->Arguments[0], &SPIRV::IDRegClass);
     MRI->setRegClass(Call->Arguments[1], &SPIRV::IDRegClass);
     MRI->setRegClass(Call->Arguments[3], &SPIRV::IDRegClass);

llvm/lib/Target/SPIRV/SPIRVCallLowering.cpp

@@ -157,22 +157,22 @@ static SPIRVType *getArgSPIRVType(const Function &F, unsigned ArgIdx,
       isSpecialOpaqueType(OriginalArgType))
     return GR->getOrCreateSPIRVType(OriginalArgType, MIRBuilder, ArgAccessQual);
 
-  MDString *MDKernelArgType = getOCLKernelArgType(F, ArgIdx);
-  if (!MDKernelArgType || (!MDKernelArgType->getString().ends_with("*") &&
-                           !MDKernelArgType->getString().ends_with("_t")))
-    return GR->getOrCreateSPIRVType(OriginalArgType, MIRBuilder, ArgAccessQual);
-
-  if (MDKernelArgType->getString().ends_with("*"))
-    return GR->getOrCreateSPIRVTypeByName(
-        MDKernelArgType->getString(), MIRBuilder,
-        addressSpaceToStorageClass(OriginalArgType->getPointerAddressSpace()));
-
-  if (MDKernelArgType->getString().ends_with("_t"))
-    return GR->getOrCreateSPIRVTypeByName(
-        "opencl." + MDKernelArgType->getString().str(), MIRBuilder,
-        SPIRV::StorageClass::Function, ArgAccessQual);
-
-  llvm_unreachable("Unable to recognize argument type name.");
+  SPIRVType *ResArgType = nullptr;
+  if (MDString *MDKernelArgType = getOCLKernelArgType(F, ArgIdx)) {
+    StringRef MDTypeStr = MDKernelArgType->getString();
+    if (MDTypeStr.ends_with("*"))
+      ResArgType = GR->getOrCreateSPIRVTypeByName(
+          MDTypeStr, MIRBuilder,
+          addressSpaceToStorageClass(
+              OriginalArgType->getPointerAddressSpace()));
+    else if (MDTypeStr.ends_with("_t"))
+      ResArgType = GR->getOrCreateSPIRVTypeByName(
+          "opencl." + MDTypeStr.str(), MIRBuilder,
+          SPIRV::StorageClass::Function, ArgAccessQual);
+  }
+  return ResArgType ? ResArgType
+                    : GR->getOrCreateSPIRVType(OriginalArgType, MIRBuilder,
+                                               ArgAccessQual);
 }
 
 static bool isEntryPoint(const Function &F) {

llvm/lib/Target/SPIRV/SPIRVGlobalRegistry.cpp

@@ -443,8 +443,9 @@ Register SPIRVGlobalRegistry::buildConstantSampler(
   SPIRVType *SampTy;
   if (SpvType)
     SampTy = getOrCreateSPIRVType(getTypeForSPIRVType(SpvType), MIRBuilder);
-  else
-    SampTy = getOrCreateSPIRVTypeByName("opencl.sampler_t", MIRBuilder);
+  else if ((SampTy = getOrCreateSPIRVTypeByName("opencl.sampler_t",
+                                                MIRBuilder)) == nullptr)
+    report_fatal_error("Unable to recognize SPIRV type name: opencl.sampler_t");
 
   auto Sampler =
       ResReg.isValid()
@@ -942,6 +943,7 @@ SPIRVGlobalRegistry::checkSpecialInstr(const SPIRV::SpecialTypeDescriptor &TD,
   return nullptr;
 }
 
+// Returns nullptr if unable to recognize SPIRV type name
 // TODO: maybe use tablegen to implement this.
 SPIRVType *SPIRVGlobalRegistry::getOrCreateSPIRVTypeByName(
     StringRef TypeStr, MachineIRBuilder &MIRBuilder,
@@ -993,8 +995,10 @@ SPIRVType *SPIRVGlobalRegistry::getOrCreateSPIRVTypeByName(
   } else if (TypeStr.starts_with("double")) {
     Ty = Type::getDoubleTy(Ctx);
     TypeStr = TypeStr.substr(strlen("double"));
-  } else
-    llvm_unreachable("Unable to recognize SPIRV type name.");
+  } else {
+    // Unable to recognize SPIRV type name
+    return nullptr;
+  }
 
   auto SpirvTy = getOrCreateSPIRVType(Ty, MIRBuilder, AQ);
 

llvm/lib/Target/SPIRV/SPIRVGlobalRegistry.h

@@ -138,6 +138,7 @@ class SPIRVGlobalRegistry {
 
   // Either generate a new OpTypeXXX instruction or return an existing one
   // corresponding to the given string containing the name of the builtin type.
+  // Return nullptr if unable to recognize SPIRV type name from `TypeStr`.
   SPIRVType *getOrCreateSPIRVTypeByName(
       StringRef TypeStr, MachineIRBuilder &MIRBuilder,
       SPIRV::StorageClass::StorageClass SC = SPIRV::StorageClass::Function,

llvm/test/CodeGen/SPIRV/pointers/custom-kernel-arg-type.ll

@@ -0,0 +1,34 @@
+; RUN: llc -O0 -mtriple=spirv32-unknown-unknown %s -o - | FileCheck %s
+; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv64-unknown-unknown %s -o - -filetype=obj | spirv-val %}
+
+; CHECK: %[[TyInt:.*]] = OpTypeInt 8 0
+; CHECK: %[[TyPtr:.*]] = OpTypePointer {{[a-zA-Z]+}} %[[TyInt]]
+; CHECK: OpFunctionParameter %[[TyPtr]]
+; CHECK: OpFunctionParameter %[[TyPtr]]
+
+%struct.my_kernel_data = type { i32, i32, i32, i32, i32 }
+%struct.my_struct = type { i32, i32 }
+
+define spir_kernel void @test(ptr addrspace(1) %in, ptr addrspace(1) %outData) !kernel_arg_type !5 {
+entry:
+  ret void
+}
+
+!llvm.module.flags = !{!0}
+!opencl.enable.FP_CONTRACT = !{}
+!opencl.ocl.version = !{!1}
+!opencl.spir.version = !{!2}
+!opencl.used.extensions = !{!3}
+!opencl.used.optional.core.features = !{!3}
+!opencl.compiler.options = !{!3}
+!llvm.ident = !{!4}
+!opencl.kernels = !{!6}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 1, i32 0}
+!2 = !{i32 1, i32 2}
+!3 = !{}
+!4 = !{!"clang version 6.0.0"}
+!5 = !{!"my_kernel_data*", !"struct my_struct*"}
+!6 = !{ptr @test}
+