[llvm] [HLSLSemanticSignatures] Implement the stacked packing of elements (PR #218060)

[Finn Plummer via llvm-commits]

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@@ -0,0 +1,62 @@
+//===- SemanticSignaturePacking.h - HLSL signature packing helpers -------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file This file declares helpers for packing HLSL semantic signatures.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_FRONTEND_HLSL_SEMANTICSIGNATUREPACKING_H
+#define LLVM_FRONTEND_HLSL_SEMANTICSIGNATUREPACKING_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/Frontend/HLSL/SemanticSignatures.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Error.h"
+#include "llvm/TargetParser/Triple.h"
+
+namespace llvm::hlsl {
+
+static constexpr unsigned MaxSignatureRows = 32;
+static constexpr unsigned MaxSignatureCols = 4;
+
+/// Denotes the element that could not be packed and why.
+class SignaturePackingError : public ErrorInfo<SignaturePackingError> {
+public:
+  enum ErrorKind {
+    SignatureOverflow,
+  };
+
+  LLVM_ABI static char ID;
+
+  SignaturePackingError(ErrorKind Kind, unsigned ElementIndex)
+      : Kind(Kind), ElementIndex(ElementIndex) {}
+
+  ErrorKind getErrorKind() const { return Kind; }
+  unsigned getElementIndex() const { return ElementIndex; }
+
+  LLVM_ABI void log(raw_ostream &OS) const override;
+
+  std::error_code convertToErrorCode() const override {
+    return llvm::inconvertibleErrorCode();
+  }
+
+private:
+  ErrorKind Kind;
+  unsigned ElementIndex;
+};
+
+/// Packs eligible signature elements into consecutive rows.
+///
+/// See llvm/docs/DirectX/SemanticSignatures.md#stacked-packing for details.
+LLVM_ABI Error
+packSignatureStacked(MutableArrayRef<SemanticSignatureElement> Elements,
+                     Triple::EnvironmentType ShaderStage, IOType IOTy);
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inbelic wrote:

Updated to return an expected and the docs as suggested

https://github.com/llvm/llvm-project/pull/218060