[RISC-V][LoongArch64] JIT: pass structs according to floating-point calling convention properly

src/coreclr/jit/codegencommon.cpp

@@ -3201,6 +3201,13 @@ var_types CodeGen::genParamStackType(LclVarDsc* dsc, const ABIPassingSegment& se
             // can always use the full register size here. This allows us to
             // use stp more often.
             return TYP_I_IMPL;
+#elif defined(TARGET_RISCV64) || defined(TARGET_LOONGARCH64)
+            // On RISC-V/LoongArch structs passed according to floating-point calling convention are enregistered one
+            // field per register regardless of the field layout in memory, so the small int load/store instructions
+            // must not be upsized to 4 bytes, otherwise for example:
+            // * struct { struct{} e1,e2,e3; byte b; float f; } -- 4-byte store for 'b' would trash 'f'
+            // * struct { float f; struct{} e1,e2,e3; byte b; } -- 4-byte store for 'b' would trash adjacent stack slot
+            return seg.GetRegisterType();
 #else
             return genActualType(seg.GetRegisterType());
 #endif
@@ -7390,18 +7397,19 @@ void CodeGen::genStructReturn(GenTree* treeNode)
         assert(varDsc->lvIsMultiRegRet);
 
 #if defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)
-        // On LoongArch64, for a struct like "{ int, double }", "retTypeDesc" will be "{ TYP_INT, TYP_DOUBLE }",
-        // i. e. not include the padding for the first field, and so the general loop below won't work.
-        var_types type  = retTypeDesc.GetReturnRegType(0);
-        regNumber toReg = retTypeDesc.GetABIReturnReg(0, compiler->info.compCallConv);
-        GetEmitter()->emitIns_R_S(ins_Load(type), emitTypeSize(type), toReg, lclNode->GetLclNum(), 0);
+        var_types type   = retTypeDesc.GetReturnRegType(0);
+        unsigned  offset = retTypeDesc.GetReturnFieldOffset(0);
+        regNumber toReg  = retTypeDesc.GetABIReturnReg(0, compiler->info.compCallConv);
+
+        GetEmitter()->emitIns_R_S(ins_Load(type), emitTypeSize(type), toReg, lclNode->GetLclNum(), offset);
         if (regCount > 1)
         {
             assert(regCount == 2);
-            int offset = genTypeSize(type);
-            type       = retTypeDesc.GetReturnRegType(1);
-            offset     = (int)((unsigned int)offset < genTypeSize(type) ? genTypeSize(type) : offset);
-            toReg      = retTypeDesc.GetABIReturnReg(1, compiler->info.compCallConv);
+            assert(offset + genTypeSize(type) <= retTypeDesc.GetReturnFieldOffset(1));
+            type   = retTypeDesc.GetReturnRegType(1);
+            offset = retTypeDesc.GetReturnFieldOffset(1);
+            toReg  = retTypeDesc.GetABIReturnReg(1, compiler->info.compCallConv);
+
             GetEmitter()->emitIns_R_S(ins_Load(type), emitTypeSize(type), toReg, lclNode->GetLclNum(), offset);
         }
 #else // !TARGET_LOONGARCH64 && !TARGET_RISCV64
@@ -7779,6 +7787,11 @@ void CodeGen::genMultiRegStoreToLocal(GenTreeLclVar* lclNode)
         assert(regCount == varDsc->lvFieldCnt);
     }
 
+#if defined(TARGET_RISCV64) || defined(TARGET_LOONGARCH64)
+    // genMultiRegStoreToLocal is only used for calls on RISC-V and LoongArch
+    const ReturnTypeDesc* returnTypeDesc = actualOp1->AsCall()->GetReturnTypeDesc();
+#endif
+
 #ifdef SWIFT_SUPPORT
     const uint32_t* offsets = nullptr;
     if (actualOp1->IsCall() && (actualOp1->AsCall()->GetUnmanagedCallConv() == CorInfoCallConvExtension::Swift))
@@ -7829,8 +7842,8 @@ void CodeGen::genMultiRegStoreToLocal(GenTreeLclVar* lclNode)
         else
         {
 #if defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)
-            // should consider the padding field within a struct.
-            offset = (offset % genTypeSize(srcType)) ? AlignUp(offset, genTypeSize(srcType)) : offset;
+            // Should consider the padding, empty struct fields, etc within a struct.
+            offset = returnTypeDesc->GetReturnFieldOffset(i);
 #endif
 #ifdef SWIFT_SUPPORT
             if (offsets != nullptr)

src/coreclr/jit/compiler.cpp

@@ -743,7 +743,7 @@ var_types Compiler::getArgTypeForStruct(CORINFO_CLASS_HANDLE clsHnd,
 
                 // Otherwise we pass this struct by value on the stack
                 // setup wbPassType and useType indicate that this is passed by value according to the X86/ARM32 ABI
-                // On LOONGARCH64 struct that is 1-16 bytes is passed by value in one/two register(s)
+                // On LOONGARCH64 and RISCV64 struct that is 1-16 bytes is passed by value in one/two register(s)
                 howToPassStruct = SPK_ByValue;
                 useType         = TYP_STRUCT;
 

src/coreclr/jit/gentree.cpp

@@ -29478,6 +29478,15 @@ void ReturnTypeDesc::InitializeStructReturnType(Compiler*                comp,
             assert(returnType != TYP_UNKNOWN);
             assert(returnType != TYP_STRUCT);
             m_regType[0] = returnType;
+
+#if defined(TARGET_RISCV64) || defined(TARGET_LOONGARCH64)
+            const CORINFO_FPSTRUCT_LOWERING* lowering = comp->GetFpStructLowering(retClsHnd);
+            if (!lowering->byIntegerCallConv)
+            {
+                assert(lowering->numLoweredElements == 1);
+                m_fieldOffset[0] = lowering->offsets[0];
+            }
+#endif // defined(TARGET_RISCV64) || defined(TARGET_LOONGARCH64)
             break;
         }
 
@@ -29543,37 +29552,36 @@ void ReturnTypeDesc::InitializeStructReturnType(Compiler*                comp,
             }
 
 #elif defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)
-            assert((structSize >= TARGET_POINTER_SIZE) && (structSize <= (2 * TARGET_POINTER_SIZE)));
+            assert(structSize > sizeof(float));
+            assert(structSize <= (2 * TARGET_POINTER_SIZE));
             BYTE gcPtrs[2] = {TYPE_GC_NONE, TYPE_GC_NONE};
             comp->info.compCompHnd->getClassGClayout(retClsHnd, &gcPtrs[0]);
             const CORINFO_FPSTRUCT_LOWERING* lowering = comp->GetFpStructLowering(retClsHnd);
             if (!lowering->byIntegerCallConv)
             {
                 comp->compFloatingPointUsed = true;
                 assert(lowering->numLoweredElements == MAX_RET_REG_COUNT);
-                var_types types[MAX_RET_REG_COUNT] = {JITtype2varType(lowering->loweredElements[0]),
-                                                      JITtype2varType(lowering->loweredElements[1])};
-                assert(varTypeIsFloating(types[0]) || varTypeIsFloating(types[1]));
-                assert((structSize > 8) == ((genTypeSize(types[0]) == 8) || (genTypeSize(types[1]) == 8)));
+                static_assert(MAX_RET_REG_COUNT == MAX_FPSTRUCT_LOWERED_ELEMENTS, "");
                 for (unsigned i = 0; i < MAX_RET_REG_COUNT; ++i)
                 {
-                    if (varTypeIsFloating(types[i]))
-                    {
-                        m_regType[i] = types[i];
-                    }
-                    else
+                    m_regType[i]     = JITtype2varType(lowering->loweredElements[i]);
+                    m_fieldOffset[i] = lowering->offsets[i];
+                    if (m_regType[i] == TYP_LONG && ((m_fieldOffset[i] % TARGET_POINTER_SIZE) == 0))
                     {
-                        assert(varTypeIsIntegralOrI(types[i]));
-                        m_regType[i] = (genTypeSize(types[i]) == 8) ? comp->getJitGCType(gcPtrs[i]) : TYP_INT;
+                        unsigned slot = m_fieldOffset[i] / TARGET_POINTER_SIZE;
+                        m_regType[i]  = comp->getJitGCType(gcPtrs[slot]);
                     }
                 }
+                assert(varTypeIsFloating(m_regType[0]) || varTypeIsFloating(m_regType[1]));
             }
             else
             {
                 for (unsigned i = 0; i < 2; ++i)
                 {
                     m_regType[i] = comp->getJitGCType(gcPtrs[i]);
                 }
+                m_fieldOffset[0] = 0;
+                m_fieldOffset[1] = TARGET_POINTER_SIZE;
             }
 
 #elif defined(TARGET_X86)

src/coreclr/jit/gentree.h

@@ -4275,6 +4275,13 @@ struct ReturnTypeDesc
 private:
     var_types m_regType[MAX_RET_REG_COUNT];
 
+#if defined(TARGET_RISCV64) || defined(TARGET_LOONGARCH64)
+    // Structs according to hardware floating-point calling convention are passed as two logical fields, each in
+    // separate register, disregarding struct layout such as packing, custom alignment, padding with empty structs, etc.
+    // We need size (can be derived from m_regType) & offset of each field for memory load/stores
+    unsigned m_fieldOffset[MAX_RET_REG_COUNT];
+#endif
+
 #ifdef DEBUG
     bool m_inited;
 #endif
@@ -4306,6 +4313,9 @@ struct ReturnTypeDesc
         for (unsigned i = 0; i < MAX_RET_REG_COUNT; ++i)
         {
             m_regType[i] = TYP_UNKNOWN;
+#if defined(TARGET_RISCV64) || defined(TARGET_LOONGARCH64)
+            m_fieldOffset[i] = 0;
+#endif
         }
 #ifdef DEBUG
         m_inited = false;
@@ -4351,8 +4361,11 @@ struct ReturnTypeDesc
         for (unsigned i = regCount + 1; i < MAX_RET_REG_COUNT; ++i)
         {
             assert(m_regType[i] == TYP_UNKNOWN);
-        }
+#if defined(TARGET_RISCV64) || defined(TARGET_LOONGARCH64)
+            assert(m_fieldOffset[i] == 0);
 #endif
+        }
+#endif // DEBUG
 
         return regCount;
     }
@@ -4401,6 +4414,25 @@ struct ReturnTypeDesc
         return result;
     }
 
+    unsigned GetSingleReturnFieldOffset() const
+    {
+        assert(!IsMultiRegRetType());
+        assert(m_regType[0] != TYP_UNKNOWN);
+#if defined(TARGET_RISCV64) || defined(TARGET_LOONGARCH64)
+        return m_fieldOffset[0];
+#else
+        return 0;
+#endif
+    }
+
+#if defined(TARGET_RISCV64) || defined(TARGET_LOONGARCH64)
+    unsigned GetReturnFieldOffset(unsigned index) const
+    {
+        assert(m_regType[index] != TYP_UNKNOWN);
+        return m_fieldOffset[index];
+    }
+#endif
+
     // Get i'th ABI return register
     regNumber GetABIReturnReg(unsigned idx, CorInfoCallConvExtension callConv) const;
 
@@ -4508,9 +4540,6 @@ struct CallArgABIInformation
         : NumRegs(0)
         , ByteOffset(0)
         , ByteSize(0)
-#if defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)
-        , StructFloatFieldType()
-#endif
         , ArgType(TYP_UNDEF)
         , PassedByRef(false)
 #if FEATURE_ARG_SPLIT
@@ -4537,18 +4566,6 @@ struct CallArgABIInformation
     unsigned NumRegs;
     unsigned ByteOffset;
     unsigned ByteSize;
-#if defined(UNIX_AMD64_ABI)
-    // Unix amd64 will split floating point types and integer types in structs
-    // between floating point and general purpose registers. Keep track of that
-    // information so we do not need to recompute it later.
-    SYSTEMV_AMD64_CORINFO_STRUCT_REG_PASSING_DESCRIPTOR StructDesc;
-#endif // UNIX_AMD64_ABI
-#if defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)
-    // For LoongArch64's and RISC-V 64's ABI, the struct which has float field(s) and no more than two fields
-    // may be passed by float register(s).
-    // e.g  `struct {int a; float b;}` passed by an integer register and a float register.
-    var_types StructFloatFieldType[2];
-#endif
     // The type used to pass this argument. This is generally the original
     // argument type, but when a struct is passed as a scalar type, this is
     // that type. Note that if a struct is passed by reference, this will still

src/coreclr/jit/lclvars.cpp

@@ -914,40 +914,37 @@ void Compiler::lvaInitUserArgs(InitVarDscInfo* varDscInfo, unsigned skipArgs, un
         if ((lowering != nullptr) && !lowering->byIntegerCallConv)
         {
             assert(varTypeIsStruct(argType));
-            int floatNum = 0;
+            assert((lowering->numLoweredElements == 1) || (lowering->numLoweredElements == 2));
             if (lowering->numLoweredElements == 1)
-            {
-                assert(argSize <= 8);
                 assert(varDsc->lvExactSize() <= argSize);
 
-                floatNum              = 1;
-                canPassArgInRegisters = varDscInfo->canEnreg(TYP_DOUBLE, 1);
+            cSlotsToEnregister  = lowering->numLoweredElements;
+            argRegTypeInStruct1 = JITtype2varType(lowering->loweredElements[0]);
+            if (lowering->numLoweredElements == 2)
+                argRegTypeInStruct2 = JITtype2varType(lowering->loweredElements[1]);
 
-                argRegTypeInStruct1 = JITtype2varType(lowering->loweredElements[0]);
-                assert(varTypeIsFloating(argRegTypeInStruct1));
-            }
-            else
+            int floatNum = (int)varTypeIsFloating(argRegTypeInStruct1) + (int)varTypeIsFloating(argRegTypeInStruct2);
+            assert(floatNum > 0);
+
+            canPassArgInRegisters = varDscInfo->canEnreg(TYP_DOUBLE, floatNum);
+            if (canPassArgInRegisters && (floatNum < lowering->numLoweredElements))
             {
+                assert(floatNum == 1);
                 assert(lowering->numLoweredElements == 2);
-                argRegTypeInStruct1 = genActualType(JITtype2varType(lowering->loweredElements[0]));
-                argRegTypeInStruct2 = genActualType(JITtype2varType(lowering->loweredElements[1]));
-                floatNum = (int)varTypeIsFloating(argRegTypeInStruct1) + (int)varTypeIsFloating(argRegTypeInStruct2);
-                canPassArgInRegisters = varDscInfo->canEnreg(TYP_DOUBLE, floatNum);
-                if (floatNum == 1)
-                    canPassArgInRegisters = canPassArgInRegisters && varDscInfo->canEnreg(TYP_I_IMPL, 1);
+                assert(varTypeIsIntegralOrI(argRegTypeInStruct1) || varTypeIsIntegralOrI(argRegTypeInStruct2));
+                canPassArgInRegisters = varDscInfo->canEnreg(TYP_I_IMPL, 1);
             }
 
-            assert((floatNum == 1) || (floatNum == 2));
-
             if (!canPassArgInRegisters)
             {
-                // On LoongArch64 and RISCV64, if there aren't any remaining floating-point registers to pass the
-                // argument, integer registers (if any) are used instead.
-                canPassArgInRegisters = varDscInfo->canEnreg(argType, cSlotsToEnregister);
-
+                // If a struct eligible for passing according to floating-point calling convention cannot be fully
+                // enregistered, it is passed according to integer calling convention -- in up to two integer registers
+                // and/or stack slots, as a lump of bits laid out like in memory.
+                cSlotsToEnregister  = cSlots;
                 argRegTypeInStruct1 = TYP_UNKNOWN;
                 argRegTypeInStruct2 = TYP_UNKNOWN;
 
+                canPassArgInRegisters = varDscInfo->canEnreg(argType, cSlotsToEnregister);
                 if (cSlotsToEnregister == 2)
                 {
                     if (!canPassArgInRegisters && varDscInfo->canEnreg(TYP_I_IMPL, 1))
@@ -1082,7 +1079,7 @@ void Compiler::lvaInitUserArgs(InitVarDscInfo* varDscInfo, unsigned skipArgs, un
                         varDsc->SetOtherArgReg(
                             genMapRegArgNumToRegNum(secondAllocatedRegArgNum, argRegTypeInStruct2, info.compCallConv));
                     }
-                    else if (cSlots > 1)
+                    else if (cSlotsToEnregister > 1)
                     {
                         // Here a struct-arg which needs two registers but only one integer register available,
                         // it has to be split. But we reserved extra 8-bytes for the whole struct.

src/coreclr/jit/lower.cpp

@@ -4847,12 +4847,14 @@ GenTree* Lowering::LowerStoreLocCommon(GenTreeLclVarCommon* lclStore)
             // x86 uses it only for long return type, not for structs.
             assert(slotCount == 1);
             assert(lclRegType != TYP_UNDEF);
-#else  // !TARGET_XARCH || UNIX_AMD64_ABI
+#else // !TARGET_XARCH || UNIX_AMD64_ABI
             if (!comp->IsHfa(layout->GetClassHandle()))
             {
                 if (slotCount > 1)
                 {
+#if !defined(TARGET_RISCV64) && !defined(TARGET_LOONGARCH64)
                     assert(call->HasMultiRegRetVal());
+#endif
                 }
                 else
                 {
@@ -5158,6 +5160,7 @@ void Lowering::LowerRetSingleRegStructLclVar(GenTreeUnOp* ret)
             // Otherwise we don't mind that we leave the upper bits undefined.
             lclVar->ChangeType(ret->TypeGet());
         }
+        lclVar->AsLclFld()->SetLclOffs(comp->compRetTypeDesc.GetSingleReturnFieldOffset());
     }
     else
     {
@@ -5346,7 +5349,8 @@ GenTreeLclVar* Lowering::SpillStructCallResult(GenTreeCall* call) const
     comp->lvaSetVarDoNotEnregister(spillNum DEBUGARG(DoNotEnregisterReason::LocalField));
     CORINFO_CLASS_HANDLE retClsHnd = call->gtRetClsHnd;
     comp->lvaSetStruct(spillNum, retClsHnd, false);
-    GenTreeLclFld* spill = comp->gtNewStoreLclFldNode(spillNum, call->TypeGet(), 0, call);
+    unsigned       offset = call->GetReturnTypeDesc()->GetSingleReturnFieldOffset();
+    GenTreeLclFld* spill  = comp->gtNewStoreLclFldNode(spillNum, call->TypeGet(), offset, call);
 
     BlockRange().InsertAfter(call, spill);
     ContainCheckStoreLoc(spill);