From e5fdceb9b869f010a2a75638fd38aaf1867f3008 Mon Sep 17 00:00:00 2001
From: Richard-Qin-X <richard.qin.001@gmail.com>
Date: Sun, 9 Aug 2026 04:40:17 +0800
Subject: [CodeGen] Complete register allocation infrastructure

---
 backend/lib/CodeGen/RegAllocBasic.cpp | 136 ++++++++++++++++++++++++++++++++++
 1 file changed, 136 insertions(+)
 create mode 100644 backend/lib/CodeGen/RegAllocBasic.cpp

(limited to 'backend/lib/CodeGen/RegAllocBasic.cpp')

diff --git a/backend/lib/CodeGen/RegAllocBasic.cpp b/backend/lib/CodeGen/RegAllocBasic.cpp
new file mode 100644
index 0000000..4bb7b23
--- /dev/null
+++ b/backend/lib/CodeGen/RegAllocBasic.cpp
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "RegAllocBasic.h"
+
+#include "RegAllocBase.h"
+#include "rcc/CodeGen/LiveRegMatrix.h"
+#include "rcc/CodeGen/MachineLiveness.h"
+
+#include <algorithm>
+#include <memory>
+#include <ranges>
+
+namespace rcc {
+namespace {
+
+class BasicAllocatorEngine final : public RegAllocBase {
+public:
+  BasicAllocatorEngine(MachineFunction &Function, const TargetDescription &Target,
+                       const TargetRegisterAllocationInfo &TargetInfo,
+                       MachineAnalysisManager &Analyses, RegisterAllocationOptions Options)
+      : RegAllocBase(Function, Target, TargetInfo, Analyses, Options) {}
+
+private:
+  [[nodiscard]] Expected<AllocationRoundResult>
+  allocateRound(const LiveIntervalsAnalysis::Result &Intervals, VirtRegMap &Mapping) override {
+    LiveRegMatrix Matrix(Function, Target, Intervals);
+    AllocationRoundResult Result;
+    std::vector<const LiveInterval *> Worklist = orderedAllocationIntervals(Intervals, Function);
+    std::ranges::stable_sort(Worklist, [&](const LiveInterval *Left, const LiveInterval *Right) {
+      const bool LeftSpillable = Mapping.isSpillable(Left->Reg);
+      const bool RightSpillable = Mapping.isSpillable(Right->Reg);
+      if (LeftSpillable != RightSpillable)
+        return !LeftSpillable;
+      if (Left->SpillWeight != Right->SpillWeight)
+        return Left->SpillWeight > Right->SpillWeight;
+      return false;
+    });
+    for (const LiveInterval *Interval : Worklist) {
+      const Register VirtualReg = Interval->Reg;
+      if (regalloc_detail::hasTerminatorDefinition(Function, Target, VirtualReg)) {
+        auto Marked = Mapping.setSpillable(VirtualReg, false);
+        if (!Marked)
+          return std::unexpected(Marked.error());
+      }
+      auto Candidates = regalloc_detail::allocationOrder(Function, Target, VirtualReg);
+      if (!Candidates)
+        return std::unexpected(Candidates.error());
+      bool Assigned = false;
+      for (const PhysicalRegister Candidate : *Candidates) {
+        if (Matrix.checkInterference(VirtualReg, Candidate).Kind != RegisterInterferenceKind::Free)
+          continue;
+        auto MatrixAssignment = Matrix.assign(VirtualReg, Candidate);
+        if (!MatrixAssignment)
+          continue;
+        auto MapAssignment = Mapping.assign(VirtualReg, Candidate);
+        if (!MapAssignment)
+          return std::unexpected(MapAssignment.error());
+        Assigned = true;
+        break;
+      }
+      if (!Assigned) {
+        if (!Mapping.isSpillable(VirtualReg)) {
+          return makeUnexpected(ErrorCode::RegisterAllocationFailed,
+                                "BasicAllocator cannot assign a non-spillable virtual register");
+        }
+        Result.Spilled.push_back(VirtualReg);
+      }
+    }
+    return Result;
+  }
+};
+
+[[nodiscard]] const MachinePassContract &basicContract() {
+  static const MachinePassContract Contract = [] {
+    MachinePassContract Value{
+        .Name = "BasicAllocator",
+        .Requires = {MachineFunctionProperty::Selected, MachineFunctionProperty::NoPHIs,
+                     MachineFunctionProperty::TiedOpsRewritten,
+                     MachineFunctionProperty::TracksLiveness},
+        .Sets = {MachineFunctionProperty::NoVRegs},
+        .Clears = {},
+        .RequiredAnalyses = {MachineAnalysisManager::id<LiveIntervalsAnalysis>()},
+        .VerificationStage = PipelineStage::RegisterAllocated,
+    };
+    Value.ThreadSafety = PassThreadSafety::ThreadSafe;
+    return Value;
+  }();
+  return Contract;
+}
+
+} // namespace
+
+const MachinePassContract &BasicAllocatorPass::contract() const noexcept {
+  return basicContract();
+}
+
+Expected<MachinePassResult> BasicAllocatorPass::run(MachineFunction &Function,
+                                                    const TargetDescription &Target,
+                                                    MachineAnalysisManager &Analyses) {
+  if (Info == nullptr)
+    return makeUnexpected(ErrorCode::InvalidArgument, "BasicAllocator requires target behavior");
+  auto Required = regalloc_detail::requireAllocationProperties(Function, contract());
+  if (!Required)
+    return std::unexpected(Required.error());
+  auto Trial = regalloc_detail::cloneForAllocation(Function, Target);
+  if (!Trial)
+    return std::unexpected(Trial.error());
+  MachineAnalysisManager TrialAnalyses;
+  auto Registered = registerStage11MachineAnalyses(TrialAnalyses);
+  if (!Registered)
+    return std::unexpected(Registered.error());
+  BasicAllocatorEngine TrialAllocator(*Trial->ClonedFunction, Target, *Info, TrialAnalyses,
+                                      Options);
+  auto TrialRun = TrialAllocator.run();
+  if (!TrialRun)
+    return std::unexpected(TrialRun.error());
+  auto TrialVerification =
+      regalloc_detail::verifyAllocationTrial(*Trial->ClonedFunction, Target, contract());
+  if (!TrialVerification)
+    return std::unexpected(TrialVerification.error());
+  BasicAllocatorEngine Allocator(Function, Target, *Info, Analyses, Options);
+  auto Allocated = Allocator.run();
+  if (!Allocated) {
+    return std::unexpected(regalloc_detail::withPrefix(
+        Allocated.error(), "BasicAllocator diverged after a successful transaction preflight: "));
+  }
+  return regalloc_detail::passResult(*Allocated);
+}
+
+std::unique_ptr<MachineFunctionPass>
+createBasicAllocatorPass(const TargetRegisterAllocationInfo &Info,
+                         RegisterAllocationOptions Options) {
+  return std::make_unique<BasicAllocatorPass>(Info, Options);
+}
+
+} // namespace rcc
-- 
cgit v1.2.3