From df50eedaeb7a340daf4ce935d452166fae4f8755 Mon Sep 17 00:00:00 2001
From: Lixuanwang <xlwmail@nudt.edu.cn>
Date: Tue, 5 Aug 2025 01:08:42 +0800
Subject: [PATCH] =?UTF-8?q?[backend]=E5=B0=86=E6=B5=AE=E7=82=B9=E9=80=BB?=
 =?UTF-8?q?=E8=BE=91=E6=94=B9=E4=B8=BA=E4=B8=8E=E5=BC=80=E5=8F=91=E6=9D=BF?=
 =?UTF-8?q?=E4=B8=80=E8=87=B4?=
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---
 src/backend/RISCv64/RISCv64ISel.cpp | 83 ++++++++++++++++++++++++++---
 1 file changed, 77 insertions(+), 6 deletions(-)

diff --git a/src/backend/RISCv64/RISCv64ISel.cpp b/src/backend/RISCv64/RISCv64ISel.cpp
index 21e8e3c..a92171f 100644
--- a/src/backend/RISCv64/RISCv64ISel.cpp
+++ b/src/backend/RISCv64/RISCv64ISel.cpp
@@ -745,12 +745,83 @@ void RISCv64ISel::selectNode(DAGNode* node) {
                     CurMBB->addInstruction(std::move(instr));
                     break;
                 }
-                case Instruction::kFtoI: { // 浮点 to 整数 (使用硬件指令进行向零截断)
-                    // 直接生成一条带有 rtz 舍入模式的转换指令
-                    auto instr = std::make_unique<MachineInstr>(RVOpcodes::FCVT_W_S_RTZ);
-                    instr->addOperand(std::make_unique<RegOperand>(dest_vreg)); // 目标是整数vreg
-                    instr->addOperand(std::make_unique<RegOperand>(src_vreg));  // 源是浮点vreg
-                    CurMBB->addInstruction(std::move(instr));
+                case Instruction::kFtoI: { // 浮点 to 整数 (带向下取整)
+                    // 目标：实现 floor(x) 的效果, C/C++中浮点转整数是截断(truncate)
+                    // 对于正数，floor(x) == truncate(x)
+                    // RISC-V的 fcvt.w.s 默认是“四舍五入到偶数”
+                    // 我们需要手动实现截断逻辑
+                    // 逻辑:
+                    //   temp_i = fcvt.w.s(x)  // 四舍五入
+                    //   temp_f = fcvt.s.w(temp_i) // 转回浮点
+                    //   if (x < temp_f) { // 如果原数更小，说明被“五入”了
+                    //     result = temp_i - 1
+                    //   } else {
+                    //     result = temp_i
+                    //   }
+                    
+                    auto temp_i_vreg = getNewVReg(Type::getIntType());
+                    auto temp_f_vreg = getNewVReg(Type::getFloatType());
+                    auto cmp_vreg = getNewVReg(Type::getIntType());
+
+                    // 1. fcvt.w.s temp_i_vreg, src_vreg
+                    auto fcvt_w = std::make_unique<MachineInstr>(RVOpcodes::FCVT_W_S);
+                    fcvt_w->addOperand(std::make_unique<RegOperand>(temp_i_vreg));
+                    fcvt_w->addOperand(std::make_unique<RegOperand>(src_vreg));
+                    CurMBB->addInstruction(std::move(fcvt_w));
+
+                    // 2. fcvt.s.w temp_f_vreg, temp_i_vreg
+                    auto fcvt_s = std::make_unique<MachineInstr>(RVOpcodes::FCVT_S_W);
+                    fcvt_s->addOperand(std::make_unique<RegOperand>(temp_f_vreg));
+                    fcvt_s->addOperand(std::make_unique<RegOperand>(temp_i_vreg));
+                    CurMBB->addInstruction(std::move(fcvt_s));
+
+                    // 3. flt.s cmp_vreg, src_vreg, temp_f_vreg
+                    auto flt = std::make_unique<MachineInstr>(RVOpcodes::FLT_S);
+                    flt->addOperand(std::make_unique<RegOperand>(cmp_vreg));
+                    flt->addOperand(std::make_unique<RegOperand>(src_vreg));
+                    flt->addOperand(std::make_unique<RegOperand>(temp_f_vreg));
+                    CurMBB->addInstruction(std::move(flt));
+
+                    // 创建标签
+                    int unique_id = this->local_label_counter++;
+                    std::string rounded_up_label = MFunc->getName() + "_ftoi_rounded_up_" + std::to_string(unique_id);
+                    std::string done_label = MFunc->getName() + "_ftoi_done_" + std::to_string(unique_id);
+
+                    // 4. bne cmp_vreg, x0, rounded_up_label
+                    auto bne = std::make_unique<MachineInstr>(RVOpcodes::BNE);
+                    bne->addOperand(std::make_unique<RegOperand>(cmp_vreg));
+                    bne->addOperand(std::make_unique<RegOperand>(PhysicalReg::ZERO));
+                    bne->addOperand(std::make_unique<LabelOperand>(rounded_up_label));
+                    CurMBB->addInstruction(std::move(bne));
+
+                    // 5. else 分支: mv dest_vreg, temp_i_vreg
+                    auto mv = std::make_unique<MachineInstr>(RVOpcodes::MV);
+                    mv->addOperand(std::make_unique<RegOperand>(dest_vreg));
+                    mv->addOperand(std::make_unique<RegOperand>(temp_i_vreg));
+                    CurMBB->addInstruction(std::move(mv));
+
+                    // 6. j done_label
+                    auto j = std::make_unique<MachineInstr>(RVOpcodes::J);
+                    j->addOperand(std::make_unique<LabelOperand>(done_label));
+                    CurMBB->addInstruction(std::move(j));
+
+                    // 7. rounded_up_label:
+                    auto label_up = std::make_unique<MachineInstr>(RVOpcodes::LABEL);
+                    label_up->addOperand(std::make_unique<LabelOperand>(rounded_up_label));
+                    CurMBB->addInstruction(std::move(label_up));
+
+                    // 8. addiw dest_vreg, temp_i_vreg, -1
+                    auto addi = std::make_unique<MachineInstr>(RVOpcodes::ADDIW);
+                    addi->addOperand(std::make_unique<RegOperand>(dest_vreg));
+                    addi->addOperand(std::make_unique<RegOperand>(temp_i_vreg));
+                    addi->addOperand(std::make_unique<ImmOperand>(-1));
+                    CurMBB->addInstruction(std::move(addi));
+
+                    // 9. done_label:
+                    auto label_done = std::make_unique<MachineInstr>(RVOpcodes::LABEL);
+                    label_done->addOperand(std::make_unique<LabelOperand>(done_label));
+                    CurMBB->addInstruction(std::move(label_done));
+                    
                     break;
                 }
                 case Instruction::kFNeg: { // 浮点取负