From 1ff4fb953820c823ae8d5035c75bf43bf85e9c3c Mon Sep 17 00:00:00 2001
From: Richard-Qin-X <richard.qin.001@gmail.com>
Date: Sat, 15 Aug 2026 04:23:23 +0800
Subject: [RISCV][GlobalISel] Legalize scalar bit count operations

---
 .../lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp  | 61 +++++++++++++++++-----
 1 file changed, 49 insertions(+), 12 deletions(-)

(limited to 'backend/lib/Target/RISCV')

diff --git a/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp b/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
index 0dd99da..975fc9b 100644
--- a/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
+++ b/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
@@ -369,21 +369,36 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &Subtarget) {
   else
     ByteSwapActions.maxScalar(0, S64).lower();
 
-  getActionDefinitionsBuilder(
-      {opcode(GenericOpcode::G_CTLZ), opcode(GenericOpcode::G_CTTZ), opcode(GenericOpcode::G_CTLS)})
-      .maxScalar(0, S64)
-      .scalarSameSizeAs(1, 0)
-      .lower();
-  getActionDefinitionsBuilder(
-      {opcode(GenericOpcode::G_CTLZ_ZERO_POISON), opcode(GenericOpcode::G_CTTZ_ZERO_POISON)})
+  auto &CountZerosActions =
+      getActionDefinitionsBuilder({opcode(GenericOpcode::G_CTLZ), opcode(GenericOpcode::G_CTTZ)});
+  auto &CountZerosPoisonActions = getActionDefinitionsBuilder(
+      {opcode(GenericOpcode::G_CTLZ_ZERO_POISON), opcode(GenericOpcode::G_CTTZ_ZERO_POISON)});
+  if (HasZbb) {
+    CountZerosActions.legalFor({{S64, S64}})
+        .customFor({{S32, S32}})
+        .clampScalar(0, S32, S64)
+        .widenScalarToNextPow2(0)
+        .scalarSameSizeAs(1, 0);
+  } else {
+    CountZerosActions.maxScalar(0, S64).scalarSameSizeAs(1, 0).lower();
+    CountZerosPoisonActions.maxScalar(0, S64).scalarSameSizeAs(1, 0);
+  }
+  CountZerosPoisonActions.lower();
+
+  getActionDefinitionsBuilder(opcode(GenericOpcode::G_CTLS))
       .maxScalar(0, S64)
       .scalarSameSizeAs(1, 0)
       .lower();
-  getActionDefinitionsBuilder(opcode(GenericOpcode::G_CTPOP))
-      .widenScalarToNextPow2(0, 8)
-      .clampScalar(0, S8, S64)
-      .scalarSameSizeAs(1, 0)
-      .lower();
+
+  auto &CountPopulationActions = getActionDefinitionsBuilder(opcode(GenericOpcode::G_CTPOP));
+  if (HasZbb) {
+    CountPopulationActions.legalFor({{S64, S64}}).clampScalar(0, S64, S64).scalarSameSizeAs(1, 0);
+  } else {
+    CountPopulationActions.widenScalarToNextPow2(0, 8)
+        .clampScalar(0, S8, S64)
+        .scalarSameSizeAs(1, 0)
+        .lower();
+  }
 
   getActionDefinitionsBuilder(opcode(GenericOpcode::G_CONSTANT))
       .legalFor({P0})
@@ -822,6 +837,28 @@ Expected<void> RISCVLegalizerInfo::legalizeCustom(LegalizerHelper &Helper,
     Helper.Observer.changedInstr(Instruction);
     return {};
   }
+  if (Instruction.opcode() == opcode(GenericOpcode::G_CTLZ) ||
+      Instruction.opcode() == opcode(GenericOpcode::G_CTTZ) ||
+      Instruction.opcode() == opcode(GenericOpcode::G_CTLS)) {
+    auto XLenType = LowLevelType::makeCategoryNeutralScalar(64);
+    if (!XLenType)
+      return std::unexpected(XLenType.error());
+
+    Helper.Observer.changingInstr(Instruction);
+    if (auto Widened = Helper.widenScalarSrc(Instruction, *XLenType, 1, GenericOpcode::G_ANYEXT);
+        !Widened) {
+      return std::unexpected(Widened.error());
+    }
+    if (auto Widened = Helper.widenScalarDst(Instruction, *XLenType); !Widened)
+      return std::unexpected(Widened.error());
+    auto WordOpcode = getRISCVWOpcode(static_cast<GenericOpcode>(Instruction.opcode().value()));
+    if (!WordOpcode)
+      return std::unexpected(WordOpcode.error());
+    if (auto Changed = Instruction.setOpcode(*WordOpcode); !Changed)
+      return std::unexpected(Changed.error());
+    Helper.Observer.changedInstr(Instruction);
+    return {};
+  }
   if (Instruction.opcode() == opcode(GenericOpcode::G_ANYEXT) ||
       Instruction.opcode() == opcode(GenericOpcode::G_SEXT) ||
       Instruction.opcode() == opcode(GenericOpcode::G_ZEXT)) {
-- 
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