[RISC-V] Flush-to-zero behavior for float-to-int conversion

src/coreclr/jit/codegenriscv64.cpp

@@ -3380,8 +3380,26 @@ void CodeGen::genFloatToIntCast(GenTree* treeNode)
 
     genConsumeOperands(treeNode->AsOp());
 
+    regNumber tmpReg = treeNode->GetSingleTempReg();
+    assert(tmpReg != treeNode->GetRegNum());
+    assert(tmpReg != op1->GetRegNum());
+
     GetEmitter()->emitIns_R_R(ins, dstSize, treeNode->GetRegNum(), op1->GetRegNum());
 
+    // This part emulates the "flush to zero" option because the RISC-V specification does not provide it.
+    instruction feq_ins = INS_feq_s;
+    if (srcType == TYP_DOUBLE)
+    {
+        feq_ins = INS_feq_d;
+    }
+    // Compare op1 with itself to get 0 if op1 is NaN and 1 for any other value
+    GetEmitter()->emitIns_R_R_R(feq_ins, dstSize, tmpReg, op1->GetRegNum(), op1->GetRegNum());
+    // Get subtraction result of REG_ZERO (always 0) and feq result
+    // As a result we get 0 for NaN and -1 (all bits set) for any other value
+    GetEmitter()->emitIns_R_R_R(INS_sub, dstSize, tmpReg, REG_ZERO, tmpReg);
+    // and instruction with received mask produces 0 for NaN and preserves any other value
+    GetEmitter()->emitIns_R_R_R(INS_and, dstSize, treeNode->GetRegNum(), treeNode->GetRegNum(), tmpReg);
+
     genProduceReg(treeNode);
 }
 

src/coreclr/jit/emitriscv64.cpp

@@ -689,6 +689,15 @@ void emitter::emitIns_R_R_I(
         code |= ((imm >> 5) & 0x3f) << 25;
         code |= ((imm >> 12) & 0x1) << 31;
     }
+    else if (ins == INS_csrrs || ins == INS_csrrw || ins == INS_csrrc)
+    {
+        assert(isGeneralRegisterOrR0(reg1));
+        assert(isGeneralRegisterOrR0(reg2));
+        assert(isValidUimm12(imm));
+        code |= reg1 << 7;
+        code |= reg2 << 15;
+        code |= imm << 20;
+    }
     else
     {
         NYI_RISCV64("illegal ins within emitIns_R_R_I!");
@@ -704,6 +713,39 @@ void emitter::emitIns_R_R_I(
     appendToCurIG(id);
 }
 
+/*****************************************************************************
+ *
+ *  Add an instruction referencing register and two constants.
+ */
+
+void emitter::emitIns_R_I_I(
+    instruction ins, emitAttr attr, regNumber reg1, ssize_t imm1, ssize_t imm2, insOpts opt) /* = INS_OPTS_NONE */
+{
+    code_t code = emitInsCode(ins);
+
+    if (INS_csrrwi <= ins && ins <= INS_csrrci)
+    {
+        assert(isGeneralRegisterOrR0(reg1));
+        assert(isValidUimm5(imm1));
+        assert(isValidUimm12(imm2));
+        code |= reg1 << 7;
+        code |= imm1 << 15;
+        code |= imm2 << 20;
+    }
+    else
+    {
+        NYI_RISCV64("illegal ins within emitIns_R_I_I!");
+    }
+    instrDesc* id = emitNewInstr(attr);
+
+    id->idIns(ins);
+    id->idReg1(reg1);
+    id->idAddr()->iiaSetInstrEncode(code);
+    id->idCodeSize(4);
+
+    appendToCurIG(id);
+}
+
 /*****************************************************************************
  *
  *  Add an instruction referencing three registers.
@@ -3349,6 +3391,51 @@ void emitter::emitDisInsName(code_t code, const BYTE* addr, instrDesc* id)
         }
         case 0x73:
         {
+            unsigned int opcode2 = (code >> 12) & 0x7;
+            if (opcode2 != 0)
+            {
+                const char* rd      = RegNames[(code >> 7) & 0x1f];
+                int         csrtype = (code >> 20);
+                if (opcode2 <= 0x3)
+                {
+                    const char* rs1 = RegNames[(code >> 15) & 0x1f];
+                    switch (opcode2)
+                    {
+                        case 0x1: // CSRRW
+                            printf("csrrw           %s, %d, %s\n", rd, csrtype, rs1);
+                            return;
+                        case 0x2: // CSRRS
+                            printf("csrrs           %s, %d, %s\n", rd, csrtype, rs1);
+                            return;
+                        case 0x3: // CSRRC
+                            printf("csrrc           %s, %d, %s\n", rd, csrtype, rs1);
+                            return;
+                        default:
+                            printf("RISCV64 illegal instruction: 0x%08X\n", code);
+                            break;
+                    }
+                }
+                else
+                {
+                    unsigned imm5 = ((code >> 15) & 0x1f);
+                    switch (opcode2)
+                    {
+                        case 0x5: // CSRRWI
+                            printf("csrrwi           %s, %d, %d\n", rd, csrtype, imm5);
+                            return;
+                        case 0x6: // CSRRSI
+                            printf("csrrsi           %s, %d, %d\n", rd, csrtype, imm5);
+                            return;
+                        case 0x7: // CSRRCI
+                            printf("csrrci           %s, %d, %d\n", rd, csrtype, imm5);
+                            return;
+                        default:
+                            printf("RISCV64 illegal instruction: 0x%08X\n", code);
+                            break;
+                    }
+                }
+            }
+
             if (code == emitInsCode(INS_ebreak))
             {
                 printf("ebreak\n");

src/coreclr/jit/emitriscv64.h

@@ -106,6 +106,12 @@ static bool isValidUimm11(ssize_t value)
     return (0 == (value >> 11));
 }
 
+// Returns true if 'value' is a legal unsigned immediate 5 bit encoding.
+static bool isValidUimm5(ssize_t value)
+{
+    return (0 == (value >> 5));
+}
+
 // Returns true if 'value' is a legal signed immediate 20 bit encoding.
 static bool isValidSimm20(ssize_t value)
 {
@@ -189,6 +195,9 @@ void emitIns_R_R(instruction ins, emitAttr attr, regNumber reg1, regNumber reg2,
 void emitIns_R_R_I(
     instruction ins, emitAttr attr, regNumber reg1, regNumber reg2, ssize_t imm, insOpts opt = INS_OPTS_NONE);
 
+void emitIns_R_I_I(
+    instruction ins, emitAttr attr, regNumber reg1, ssize_t imm1, ssize_t imm2, insOpts opt = INS_OPTS_NONE);
+
 void emitIns_R_R_R(
     instruction ins, emitAttr attr, regNumber reg1, regNumber reg2, regNumber reg3, insOpts opt = INS_OPTS_NONE);
 

src/coreclr/jit/lsrariscv64.cpp

@@ -1269,6 +1269,12 @@ int LinearScan::BuildCast(GenTreeCast* cast)
     int srcCount = BuildOperandUses(cast->CastOp());
     BuildDef(cast);
 
+    if (varTypeIsFloating(cast->gtOp1) && !varTypeIsFloating(cast->TypeGet()))
+    {
+        buildInternalIntRegisterDefForNode(cast);
+        buildInternalRegisterUses();
+    }
+
     return srcCount;
 }
 

src/coreclr/jit/registerriscv64.h

@@ -50,6 +50,7 @@ REGDEF(T5,     30, 0x40000000, "t5"  )
 REGDEF(T6,     31, 0x80000000, "t6"  )
 
 REGALIAS(R8, FP)
+REGALIAS(ZERO, R0)
 
 #define FBASE 32
 #define FMASK(x) (1ULL << (FBASE+(x)))