[mlir][spirv] Add definitions and (de)serialization for FPRoundingMode

mlir/include/mlir/Dialect/SPIRV/IR/SPIRVBase.td

@@ -3249,6 +3249,19 @@ def SPIRV_FC_OptNoneINTEL : I32BitEnumAttrCaseBit<"OptNoneINTEL", 16> {
   ];
 }
 
+def SPIRV_FPRM_RTE : I32EnumAttrCase<"RTE", 0>;
+def SPIRV_FPRM_RTZ : I32EnumAttrCase<"RTZ", 1>;
+def SPIRV_FPRM_RTP : I32EnumAttrCase<"RTP", 2>;
+def SPIRV_FPRM_RTN : I32EnumAttrCase<"RTN", 3>;
+
+// TODO: Enforce SPIR-V spec validation rule for Shader capability: only permit
+//       FPRoundingMode on a value stored to certain storage classes?
+//       (The OpenCL environment also has FPRoundingMode rules, but different.)
+def SPIRV_FPRoundingModeAttr :
+    SPIRV_I32EnumAttr<"FPRoundingMode", "valid SPIR-V FPRoundingMode", "fp_rounding_mode", [
+      SPIRV_FPRM_RTE, SPIRV_FPRM_RTZ, SPIRV_FPRM_RTP, SPIRV_FPRM_RTN
+    ]>;
+
 def SPIRV_FunctionControlAttr :
     SPIRV_BitEnumAttr<"FunctionControl", "valid SPIR-V FunctionControl", "function_control", [
       SPIRV_FC_None, SPIRV_FC_Inline, SPIRV_FC_DontInline, SPIRV_FC_Pure, SPIRV_FC_Const,

mlir/lib/Target/SPIRV/Deserialization/Deserializer.cpp

@@ -250,6 +250,15 @@ LogicalResult spirv::Deserializer::processDecoration(ArrayRef<uint32_t> words) {
         symbol, FPFastMathModeAttr::get(opBuilder.getContext(),
                                         static_cast<FPFastMathMode>(words[2])));
     break;
+  case spirv::Decoration::FPRoundingMode:
+    if (words.size() != 3) {
+      return emitError(unknownLoc, "OpDecorate with ")
+             << decorationName << " needs a single integer literal";
+    }
+    decorations[words[0]].set(
+        symbol, FPRoundingModeAttr::get(opBuilder.getContext(),
+                                        static_cast<FPRoundingMode>(words[2])));
+    break;
   case spirv::Decoration::DescriptorSet:
   case spirv::Decoration::Binding:
     if (words.size() != 3) {

mlir/lib/Target/SPIRV/Serialization/Serializer.cpp

@@ -214,6 +214,9 @@ static std::string getDecorationName(StringRef attrName) {
   // expected FPFastMathMode.
   if (attrName == "fp_fast_math_mode")
     return "FPFastMathMode";
+  // similar here
+  if (attrName == "fp_rounding_mode")
+    return "FPRoundingMode";
 
   return llvm::convertToCamelFromSnakeCase(attrName, /*capitalizeFirst=*/true);
 }
@@ -242,6 +245,13 @@ LogicalResult Serializer::processDecorationAttr(Location loc, uint32_t resultID,
     }
     return emitError(loc, "expected FPFastMathModeAttr attribute for ")
            << stringifyDecoration(decoration);
+  case spirv::Decoration::FPRoundingMode:
+    if (auto intAttr = dyn_cast<FPRoundingModeAttr>(attr)) {
+      args.push_back(static_cast<uint32_t>(intAttr.getValue()));
+      break;
+    }
+    return emitError(loc, "expected FPRoundingModeAttr attribute for ")
+           << stringifyDecoration(decoration);
   case spirv::Decoration::Binding:
   case spirv::Decoration::DescriptorSet:
   case spirv::Decoration::Location:

mlir/test/Target/SPIRV/decorations.mlir

@@ -97,3 +97,13 @@ spirv.func @fmul_decorations(%arg: f32) -> f32 "None" {
   spirv.ReturnValue %0 : f32
 }
 }
+
+// -----
+
+spirv.module Logical GLSL450 requires #spirv.vce<v1.0, [Kernel, Float16], []> {
+spirv.func @fp_rounding_mode(%arg: f32) -> f16 "None" {
+  // CHECK: spirv.FConvert %arg0 {fp_rounding_mode = #spirv.fp_rounding_mode<RTN>} : f32 to f16
+  %0 = spirv.FConvert %arg {fp_rounding_mode = #spirv.fp_rounding_mode<RTN>} : f32 to f16
+  spirv.ReturnValue %0 : f16
+}
+}