Allow passing sized array to unsized array parameter. (shader-slang#4744)

Author: csyonghe

docs/user-guide/02-conventional-features.md

@@ -111,14 +111,54 @@ In some cases the element count is then inferred from the initial value of a var
 int a[] = { 1, 2, 3 };
 ```
 
-In other cases, the result is a _runtime-sized_ array, where the actual element count will be determined later:
+In other cases, the result is a _unsized_ array, where the actual element count will be determined later:
 
 ```hlsl
 // the type of `b` is `int[]`
 void f( int b[] )
 { ... }
 ```
 
+It is allowed to pass a sized array as argument to an unsized array parameter when calling a function.
+
+Array types has a `getCount()` memeber function that returns the length of the array.
+
+```hlsl
+int f( int b[] )
+{
+    return b.getCount(); // Note: all arguments to `b` must be resolvable to sized arrays.
+}
+
+void test()
+{
+    int arr[3] = { 1, 2, 3 };
+    int x = f(arr); // OK, passing sized array to unsized array parameter, x will be 3.
+}
+```
+
+Please note that if a function calls `getCount()` method on an unsized array parameter, then all
+calls to that function must provide a sized array argument, otherwise the compiler will not be able
+to resolve the size and will report an error. The following code shows an example of valid and
+invalid cases.
+
+```hlsl
+int f( int b[] )
+{
+    return b.getCount();
+}
+int g( int b[] )
+{
+    return f(b); // transitive calls are allowed.
+}
+uniform int unsizedParam[];
+void test()
+{
+    g(unsizedParam); // Not OK, `unsizedParam` doesn't have a known size at compile time.
+    int arr[3];
+    g(arr); // OK.
+}
+```
+
 There are more limits on how runtime-sized arrays can be used than on arrays of statically-known element count.
 
 > #### Note ####

source/slang/core.meta.slang

@@ -1040,16 +1040,15 @@ __generic<T, let N:int>
 __magic_type(ArrayExpressionType)
 struct Array : IArray<T>
 {
-    [ForceInline]
-    int getCount() { return N; }
+    __intrinsic_op($(kIROp_GetArrayLength))
+    int getCount();
 
     __subscript(int index) -> T
     {
         __intrinsic_op($(kIROp_GetElement))
         get;
     }
 }
-
     /// An `N` component vector with elements of type `T`.
 __generic<T = float, let N : int = 4>
 __magic_type(VectorExpressionType)

source/slang/slang-ast-support-types.h

@@ -96,6 +96,7 @@ namespace Slang
 
         kConversionCost_GenericParamUpcast = 1,
         kConversionCost_UnconstraintGenericParam = 20,
+        kConversionCost_SizedArrayToUnsizedArray = 30,
 
         // Convert between matrices of different layout
         kConversionCost_MatrixLayout = 5,

source/slang/slang-check-conversion.cpp

@@ -750,6 +750,31 @@ namespace Slang
             return true;
         }
 
+        // Allow implicit conversion from sized array to unsized array when
+        // calling a function.
+        // Note: we implement the logic here instead of an implicit_conversion
+        // intrinsic in the stdlib because we only want to allow this conversion
+        // when calling a function.
+        //
+        if (site == CoercionSite::Argument)
+        {
+            if (auto fromArrayType = as<ArrayExpressionType>(fromType))
+            {
+                if (auto toArrayType = as<ArrayExpressionType>(toType))
+                {
+                    if (fromArrayType->getElementType()->equals(toArrayType->getElementType())
+                        && toArrayType->isUnsized())
+                    {
+                        if (outToExpr)
+                            *outToExpr = fromExpr;
+                        if (outCost)
+                            *outCost = kConversionCost_SizedArrayToUnsizedArray;
+                        return true;
+                    }
+                }
+            }
+        }
+
         // Another important case is when either the "to" or "from" type
         // represents an error. In such a case we must have already
         // reporeted the error, so it is better to allow the conversion

source/slang/slang-diagnostic-defs.h

@@ -857,6 +857,7 @@ DIAGNOSTIC(55201, Error, unsupportedRecursion, "recursion detected in call to '$
 DIAGNOSTIC(55202, Error, systemValueAttributeNotSupported, "system value semantic '$0' is not supported for the current target.")
 DIAGNOSTIC(55203, Error, systemValueTypeIncompatible, "system value semantic '$0' should have type '$1' or be convertible to type '$1'.")
 DIAGNOSTIC(56001, Error, unableToAutoMapCUDATypeToHostType, "Could not automatically map '$0' to a host type. Automatic binding generation failed for '$1'")
+DIAGNOSTIC(56002, Error, attemptToQuerySizeOfUnsizedArray, "cannot obtain the size of an unsized array.")
 
 DIAGNOSTIC(57001, Warning, spirvOptFailed, "spirv-opt failed. $0")
 DIAGNOSTIC(57002, Error, unknownPatchConstantParameter, "unknown patch constant parameter '$0'.")

source/slang/slang-emit.cpp

@@ -947,13 +947,13 @@ Result linkAndOptimizeIR(
     specializeResourceUsage(codeGenContext, irModule);
     specializeFuncsForBufferLoadArgs(codeGenContext, irModule);
 
-    // For GLSL targets, we also want to specialize calls to functions that
-    // takes array parameters if possible, to avoid performance issues on
-    // those platforms.
-    if (isKhronosTarget(targetRequest))
-    {
-        specializeArrayParameters(codeGenContext, irModule);
-    }
+    // We also want to specialize calls to functions that
+    // takes unsized array parameters if possible.
+    // Moreover, for Khronos targets, we also want to specialize calls to functions
+    // that takes arrays/structs containing arrays as parameters with the actual
+    // global array object to avoid loading big arrays into SSA registers, which seems
+    // to cause performance issues.
+    specializeArrayParameters(codeGenContext, irModule);
 
 #if 0
     dumpIRIfEnabled(codeGenContext, irModule, "AFTER RESOURCE SPECIALIZATION");

source/slang/slang-ir-autodiff-fwd.cpp

@@ -1943,6 +1943,9 @@ InstPair ForwardDiffTranscriber::transcribeInstImpl(IRBuilder* builder, IRInst*
     case kIROp_DebugLine:
     case kIROp_DebugVar:
     case kIROp_DebugValue:
+    case kIROp_GetArrayLength:
+    case kIROp_SizeOf:
+    case kIROp_AlignOf:
         return transcribeNonDiffInst(builder, origInst);
 
         // A call to createDynamicObject<T>(arbitraryData) cannot provide a diff value,

source/slang/slang-ir-check-unsupported-inst.cpp

@@ -42,6 +42,23 @@ namespace Slang
         }
     }
 
+    void checkUnsupportedInst(TargetRequest* target, IRFunc* func, DiagnosticSink* sink)
+    {
+        SLANG_UNUSED(target);
+        for (auto block : func->getBlocks())
+        {
+            for (auto inst : block->getChildren())
+            {
+                switch (inst->getOp())
+                {
+                case kIROp_GetArrayLength:
+                    sink->diagnose(inst, Diagnostics::attemptToQuerySizeOfUnsizedArray);
+                    break;
+                }
+            }
+        }
+    }
+
     void checkUnsupportedInst(TargetRequest* target, IRModule* module, DiagnosticSink* sink)
     {
         HashSet<IRFunc*> checkedFuncsForRecursionDetection;
@@ -62,6 +79,16 @@ namespace Slang
             case kIROp_Func:
                 if (!isCPUTarget(target))
                     checkRecursion(checkedFuncsForRecursionDetection, as<IRFunc>(globalInst), sink);
+                checkUnsupportedInst(target, as<IRFunc>(globalInst), sink);
+                break;
+            case kIROp_Generic:
+                {
+                    auto generic = as<IRGeneric>(globalInst);
+                    auto innerFunc = as<IRFunc>(findGenericReturnVal(generic));
+                    if (innerFunc)
+                        checkUnsupportedInst(target, innerFunc, sink);
+                    break;
+                }
             default:
                 break;
             }

source/slang/slang-ir-inst-defs.h

@@ -1108,7 +1108,7 @@ INST(TreatAsDynamicUniform, TreatAsDynamicUniform, 1, 0)
 
 INST(SizeOf,                            sizeOf,                     1, 0)
 INST(AlignOf,                           alignOf,                    1, 0)
-
+INST(GetArrayLength,                    GetArrayLength,             1, 0)
 INST(IsType, IsType, 3, 0)
 INST(TypeEquals, TypeEquals, 2, 0)
 INST(IsInt, IsInt, 1, 0)

source/slang/slang-ir-peephole.cpp

@@ -283,6 +283,14 @@ struct PeepholeContext : InstPassBase
                 changed = true;
             }
             break;
+        case kIROp_GetArrayLength:
+            if (auto arrayType = as<IRArrayType>(inst->getOperand(0)->getDataType()))
+            {
+                inst->replaceUsesWith(arrayType->getElementCount());
+                maybeRemoveOldInst(inst);
+                changed = true;
+            }
+            break;
         case kIROp_GetResultError:
             if (inst->getOperand(0)->getOp() == kIROp_MakeResultError)
             {

source/slang/slang-ir-specialize-arrays.cpp

@@ -13,8 +13,11 @@ struct ArrayParameterSpecializationCondition : FunctionCallSpecializeCondition
     // This pass is intended to specialize functions
     // with struct parameters that has array fields
     // to avoid performance problems for GLSL targets.
-
     // Returns true if `type` is an `IRStructType` with array-typed fields.
+    // It will also specialize functions with unsized array parameters into
+    // sized arrays, if the function is called with an argument that has a
+    // sized array type.
+    //
     bool isStructTypeWithArray(IRType* type)
     {
         if (auto structType = as<IRStructType>(type))
@@ -38,15 +41,55 @@ struct ArrayParameterSpecializationCondition : FunctionCallSpecializeCondition
     bool doesParamWantSpecialization(IRParam* param, IRInst* arg)
     {
         SLANG_UNUSED(arg);
-        return isStructTypeWithArray(param->getDataType());
+        if (isKhronosTarget(codeGenContext->getTargetReq()))
+            return isStructTypeWithArray(param->getDataType());
+        return false;
     }
+
+    bool doesParamTypeWantSpecialization(IRParam* param, IRInst* arg)
+    {
+        auto paramType = param->getDataType();
+        auto argType = arg->getDataType();
+        if (auto outTypeBase = as<IROutTypeBase>(paramType))
+        {
+            paramType = outTypeBase->getValueType();
+            SLANG_ASSERT(as<IRPtrTypeBase>(argType));
+            argType = as<IRPtrTypeBase>(argType)->getValueType();
+        }
+        else if (auto refType = as<IRRefType>(paramType))
+        {
+            paramType = refType->getValueType();
+            SLANG_ASSERT(as<IRPtrTypeBase>(argType));
+            argType = as<IRPtrTypeBase>(argType)->getValueType();
+        }
+        else if (auto constRefType = as<IRConstRefType>(paramType))
+        {
+            paramType = constRefType->getValueType();
+            SLANG_ASSERT(as<IRPtrTypeBase>(argType));
+            argType = as<IRPtrTypeBase>(argType)->getValueType();
+        }
+        auto arrayType = as<IRUnsizedArrayType>(paramType);
+        if (!arrayType)
+            return false;
+        auto argArrayType = as<IRArrayType>(argType);
+        if (!argArrayType)
+            return false;
+        if (as<IRIntLit>(argArrayType->getElementCount()))
+        {
+            return true;
+        }
+        return false;
+    }
+
+    CodeGenContext* codeGenContext = nullptr;
 };
 
 void specializeArrayParameters(
     CodeGenContext* codeGenContext,
     IRModule*       module)
 {
     ArrayParameterSpecializationCondition condition;
+    condition.codeGenContext = codeGenContext;
     specializeFunctionCalls(codeGenContext, module, &condition);
 }