[RISC-V] New ABI classifier (dotnet#101114)

src/coreclr/jit/abi.cpp

@@ -281,10 +281,7 @@ bool ABIPassingInformation::IsSplitAcrossRegistersAndStack() const
 //
 ABIPassingInformation ABIPassingInformation::FromSegment(Compiler* comp, const ABIPassingSegment& segment)
 {
-    ABIPassingInformation info;
-    info.NumSegments = 1;
-    info.Segments    = new (comp, CMK_ABI) ABIPassingSegment(segment);
-    return info;
+    return {1, new (comp, CMK_ABI) ABIPassingSegment(segment)};
 }
 
 #ifdef DEBUG

src/coreclr/jit/abi.h

@@ -48,9 +48,16 @@ struct ABIPassingInformation
     // multiple register segments and a struct segment.
     // - On Windows x64, all parameters always fit into one stack slot or
     // register, and thus always have NumSegments == 1
+    // - On RISC-V, structs can be split out over 2 segments, each can be an integer/float register or a stack slot
     unsigned           NumSegments = 0;
     ABIPassingSegment* Segments    = nullptr;
 
+    ABIPassingInformation(unsigned numSegments = 0, ABIPassingSegment* segments = nullptr)
+        : NumSegments(numSegments)
+        , Segments(segments)
+    {
+    }
+
     bool HasAnyRegisterSegment() const;
     bool HasAnyStackSegment() const;
     bool HasExactlyOneRegisterSegment() const;
@@ -77,7 +84,7 @@ class RegisterQueue
     {
     }
 
-    unsigned Count()
+    unsigned Count() const
     {
         return m_numRegs - m_index;
     }
@@ -179,6 +186,22 @@ class Arm32Classifier
                                    WellKnownArg wellKnownParam);
 };
 
+class RiscV64Classifier
+{
+    const ClassifierInfo& m_info;
+    RegisterQueue         m_intRegs;
+    RegisterQueue         m_floatRegs;
+    unsigned              m_stackArgSize = 0;
+
+public:
+    RiscV64Classifier(const ClassifierInfo& info);
+
+    ABIPassingInformation Classify(Compiler*    comp,
+                                   var_types    type,
+                                   ClassLayout* structLayout,
+                                   WellKnownArg wellKnownParam);
+};
+
 #if defined(TARGET_X86)
 typedef X86Classifier PlatformClassifier;
 #elif defined(WINDOWS_AMD64_ABI)
@@ -189,6 +212,8 @@ typedef SysVX64Classifier PlatformClassifier;
 typedef Arm64Classifier PlatformClassifier;
 #elif defined(TARGET_ARM)
 typedef Arm32Classifier PlatformClassifier;
+#elif defined(TARGET_RISCV64)
+typedef RiscV64Classifier PlatformClassifier;
 #endif
 
 #ifdef SWIFT_SUPPORT

src/coreclr/jit/lclvars.cpp

@@ -1804,7 +1804,8 @@ void Compiler::lvaClassifyParameterABI()
     }
     else
 #endif
-#if defined(TARGET_X86) || defined(TARGET_AMD64) || defined(TARGET_ARM64) || defined(TARGET_ARM)
+#if defined(TARGET_X86) || defined(TARGET_AMD64) || defined(TARGET_ARM64) || defined(TARGET_ARM) ||                    \
+    defined(TARGET_RISCV64)
     {
         PlatformClassifier classifier(cInfo);
         lvaClassifyParameterABI(classifier);

src/coreclr/jit/targetriscv64.cpp

@@ -24,4 +24,154 @@ const regNumber fltArgRegs [] = {REG_FLTARG_0, REG_FLTARG_1, REG_FLTARG_2, REG_F
 const regMaskTP fltArgMasks[] = {RBM_FLTARG_0, RBM_FLTARG_1, RBM_FLTARG_2, RBM_FLTARG_3, RBM_FLTARG_4, RBM_FLTARG_5, RBM_FLTARG_6, RBM_FLTARG_7 };
 // clang-format on
 
+//-----------------------------------------------------------------------------
+// RiscV64Classifier:
+//   Construct a new instance of the RISC-V 64 ABI classifier.
+//
+// Parameters:
+//   info - Info about the method being classified.
+//
+RiscV64Classifier::RiscV64Classifier(const ClassifierInfo& info)
+    : m_info(info)
+    , m_intRegs(intArgRegs, ArrLen(intArgRegs))
+    , m_floatRegs(fltArgRegs, ArrLen(fltArgRegs))
+{
+}
+
+//-----------------------------------------------------------------------------
+// Classify:
+//   Classify a parameter for the RISC-V 64 ABI.
+//
+// Parameters:
+//   comp           - Compiler instance
+//   type           - The type of the parameter
+//   structLayout   - The layout of the struct. Expected to be non-null if
+//                    varTypeIsStruct(type) is true.
+//   wellKnownParam - Well known type of the parameter (if it may affect its ABI classification)
+//
+// Returns:
+//   Classification information for the parameter.
+//
+ABIPassingInformation RiscV64Classifier::Classify(Compiler*    comp,
+                                                  var_types    type,
+                                                  ClassLayout* structLayout,
+                                                  WellKnownArg /*wellKnownParam*/)
+{
+    assert(!m_info.IsVarArgs); // TODO: varargs currently not supported on RISC-V
+
+    StructFloatFieldInfoFlags flags     = STRUCT_NO_FLOAT_FIELD;
+    unsigned                  intFields = 0, floatFields = 0;
+    unsigned                  passedSize;
+
+    if (varTypeIsStruct(type))
+    {
+        passedSize = structLayout->GetSize();
+        if (passedSize > MAX_PASS_MULTIREG_BYTES)
+        {
+            passedSize = TARGET_POINTER_SIZE; // pass by reference
+        }
+        else if (!structLayout->IsBlockLayout())
+        {
+            flags = (StructFloatFieldInfoFlags)comp->info.compCompHnd->getRISCV64PassStructInRegisterFlags(
+                structLayout->GetClassHandle());
+
+            if ((flags & STRUCT_FLOAT_FIELD_ONLY_ONE) != 0)
+            {
+                floatFields = 1;
+            }
+            else if ((flags & STRUCT_FLOAT_FIELD_ONLY_TWO) != 0)
+            {
+                floatFields = 2;
+            }
+            else if (flags != STRUCT_NO_FLOAT_FIELD)
+            {
+                assert((flags & (STRUCT_FLOAT_FIELD_FIRST | STRUCT_FLOAT_FIELD_SECOND)) != 0);
+                floatFields = 1;
+                intFields   = 1;
+            }
+        }
+    }
+    else
+    {
+        assert(genTypeSize(type) <= TARGET_POINTER_SIZE);
+
+        if (varTypeIsFloating(type))
+            floatFields = 1;
+
+        passedSize = genTypeSize(type);
+    }
+
+    assert((floatFields > 0) || (intFields == 0));
+
+    auto PassSlot = [this](bool inFloatReg, unsigned offset, unsigned size) -> ABIPassingSegment {
+        assert(size > 0);
+        assert(size <= TARGET_POINTER_SIZE);
+        if (inFloatReg)
+        {
+            return ABIPassingSegment::InRegister(m_floatRegs.Dequeue(), offset, size);
+        }
+        else if (m_intRegs.Count() > 0)
+        {
+            return ABIPassingSegment::InRegister(m_intRegs.Dequeue(), offset, size);
+        }
+        else
+        {
+            assert((m_stackArgSize % TARGET_POINTER_SIZE) == 0);
+            ABIPassingSegment seg = ABIPassingSegment::OnStack(m_stackArgSize, offset, size);
+            m_stackArgSize += TARGET_POINTER_SIZE;
+            return seg;
+        }
+    };
+
+    if ((floatFields > 0) && (m_floatRegs.Count() >= floatFields) && (m_intRegs.Count() >= intFields))
+    {
+        // Hardware floating-point calling convention
+        if ((floatFields == 1) && (intFields == 0))
+        {
+            if (flags == STRUCT_NO_FLOAT_FIELD)
+                assert(varTypeIsFloating(type)); // standalone floating-point real
+            else
+                assert((flags & STRUCT_FLOAT_FIELD_ONLY_ONE) != 0); // struct containing just one FP real
+
+            return ABIPassingInformation::FromSegment(comp, ABIPassingSegment::InRegister(m_floatRegs.Dequeue(), 0,
+                                                                                          passedSize));
+        }
+        else
+        {
+            assert(varTypeIsStruct(type));
+            assert((floatFields + intFields) == 2);
+            assert(flags != STRUCT_NO_FLOAT_FIELD);
+            assert((flags & STRUCT_FLOAT_FIELD_ONLY_ONE) == 0);
+
+            unsigned firstSize  = ((flags & STRUCT_FIRST_FIELD_SIZE_IS8) != 0) ? 8 : 4;
+            unsigned secondSize = ((flags & STRUCT_SECOND_FIELD_SIZE_IS8) != 0) ? 8 : 4;
+            unsigned offset = max(firstSize, secondSize); // TODO: cover empty fields and custom offsets / alignments
+
+            bool isFirstFloat  = (flags & (STRUCT_FLOAT_FIELD_ONLY_TWO | STRUCT_FLOAT_FIELD_FIRST)) != 0;
+            bool isSecondFloat = (flags & (STRUCT_FLOAT_FIELD_ONLY_TWO | STRUCT_FLOAT_FIELD_SECOND)) != 0;
+            assert(isFirstFloat || isSecondFloat);
+
+            return {2, new (comp, CMK_ABI) ABIPassingSegment[]{PassSlot(isFirstFloat, 0, firstSize),
+                                                               PassSlot(isSecondFloat, offset, secondSize)}};
+        }
+    }
+    else
+    {
+        // Integer calling convention
+        if (passedSize <= TARGET_POINTER_SIZE)
+        {
+            return ABIPassingInformation::FromSegment(comp, PassSlot(false, 0, passedSize));
+        }
+        else
+        {
+            assert(varTypeIsStruct(type));
+            return {2, new (comp, CMK_ABI)
+                           ABIPassingSegment[]{PassSlot(false, 0, TARGET_POINTER_SIZE),
+                                               PassSlot(false, TARGET_POINTER_SIZE, passedSize - TARGET_POINTER_SIZE)}};
+        }
+    }
+
+    unreached();
+}
+
 #endif // TARGET_RISCV64