BPF: Generate locked insn for __sync_fetch_and_add() with cpu v1/v2 (llvm#106494)

yonghong-song · web-flow · commit 06c531e808ce · 2024-08-30T14:00:33.000-07:00
This patch contains two pars: - first to revert the patch llvm#101428. - second to remove `atomic_fetch_and_*()` to `atomic_<op>()` conversion (when return value is not used), but preserve `__sync_fetch_and_add()` to locked insn with cpu v1/v2.
diff --git a/llvm/lib/Target/BPF/BPF.h b/llvm/lib/Target/BPF/BPF.h
@@ -28,6 +28,7 @@ FunctionPass *createBPFISelDag(BPFTargetMachine &TM);
 FunctionPass *createBPFMISimplifyPatchablePass();
 FunctionPass *createBPFMIPeepholePass();
 FunctionPass *createBPFMIPreEmitPeepholePass();
+FunctionPass *createBPFMIPreEmitCheckingPass();
 
 InstructionSelector *createBPFInstructionSelector(const BPFTargetMachine &,
                                                   const BPFSubtarget &,
@@ -36,6 +37,7 @@ InstructionSelector *createBPFInstructionSelector(const BPFTargetMachine &,
 void initializeBPFCheckAndAdjustIRPass(PassRegistry&);
 void initializeBPFDAGToDAGISelLegacyPass(PassRegistry &);
 void initializeBPFMIPeepholePass(PassRegistry &);
+void initializeBPFMIPreEmitCheckingPass(PassRegistry &);
 void initializeBPFMIPreEmitPeepholePass(PassRegistry &);
 void initializeBPFMISimplifyPatchablePass(PassRegistry &);
 
diff --git a/llvm/lib/Target/BPF/BPFInstrInfo.td b/llvm/lib/Target/BPF/BPFInstrInfo.td
@@ -786,45 +786,13 @@ let Predicates = [BPFNoALU32] in {
   def : Pat<(i64 (extloadi32 ADDRri:$src)), (i64 (LDW ADDRri:$src))>;
 }
 
-// Atomic XADD for BPFNoALU32
-class XADD<BPFWidthModifer SizeOp, string OpcodeStr>
-    : TYPE_LD_ST<BPF_ATOMIC.Value, SizeOp.Value,
-                 (outs GPR:$dst),
-                 (ins MEMri:$addr, GPR:$val),
-                 "lock *("#OpcodeStr#" *)($addr) += $val",
-                 []> {
-  bits<4> dst;
-  bits<20> addr;
-
-  let Inst{51-48} = addr{19-16}; // base reg
-  let Inst{55-52} = dst;
-  let Inst{47-32} = addr{15-0}; // offset
-  let Inst{7-4} = BPF_ADD.Value;
-  let BPFClass = BPF_STX;
-}
-
 // Atomic add, and, or, xor
-class ATOMIC_NOFETCH<BPFArithOp Opc, string Opstr>
-    : TYPE_LD_ST<BPF_ATOMIC.Value, BPF_DW.Value,
+class ATOMIC_NOFETCH<BPFWidthModifer SizeOp, string OpType, RegisterClass RegTp,
+                     BPFArithOp Opc, string Opstr>
+    : TYPE_LD_ST<BPF_ATOMIC.Value, SizeOp.Value,
                  (outs GPR:$dst),
-                 (ins MEMri:$addr, GPR:$val),
-                 "lock *(u64 *)($addr) " #Opstr# "= $val",
-                 []> {
-  bits<4> dst;
-  bits<20> addr;
-
-  let Inst{51-48} = addr{19-16}; // base reg
-  let Inst{55-52} = dst;
-  let Inst{47-32} = addr{15-0}; // offset
-  let Inst{7-4} = Opc.Value;
-  let BPFClass = BPF_STX;
-}
-
-class ATOMIC32_NOFETCH<BPFArithOp Opc, string Opstr>
-    : TYPE_LD_ST<BPF_ATOMIC.Value, BPF_W.Value,
-                 (outs GPR32:$dst),
-                 (ins MEMri:$addr, GPR32:$val),
-                 "lock *(u32 *)($addr) " #Opstr# "= $val",
+                 (ins MEMri:$addr, RegTp:$val),
+                 "lock *(" #OpType# " *)($addr) " #Opstr# "= $val",
                  []> {
   bits<4> dst;
   bits<20> addr;
@@ -838,16 +806,23 @@ class ATOMIC32_NOFETCH<BPFArithOp Opc, string Opstr>
 
 let Constraints = "$dst = $val" in {
   let Predicates = [BPFHasALU32], DecoderNamespace = "BPFALU32" in {
-    def XADDW32 : ATOMIC32_NOFETCH<BPF_ADD, "+">;
-    def XANDW32 : ATOMIC32_NOFETCH<BPF_AND, "&">;
-    def XORW32  : ATOMIC32_NOFETCH<BPF_OR, "|">;
-    def XXORW32 : ATOMIC32_NOFETCH<BPF_XOR, "^">;
+    def XADDW32 : ATOMIC_NOFETCH<BPF_W, "u32", GPR32, BPF_ADD, "+">;
+    def XANDW32 : ATOMIC_NOFETCH<BPF_W, "u32", GPR32, BPF_AND, "&">;
+    def XORW32  : ATOMIC_NOFETCH<BPF_W, "u32", GPR32, BPF_OR, "|">;
+    def XXORW32 : ATOMIC_NOFETCH<BPF_W, "u32", GPR32, BPF_XOR, "^">;
   }
+  def XADDW  : ATOMIC_NOFETCH<BPF_W,  "u32", GPR, BPF_ADD, "+">;
+  def XADDD  : ATOMIC_NOFETCH<BPF_DW, "u64", GPR, BPF_ADD, "+">;
+  def XANDD  : ATOMIC_NOFETCH<BPF_DW, "u64", GPR, BPF_AND, "&">;
+  def XORD   : ATOMIC_NOFETCH<BPF_DW, "u64", GPR, BPF_OR, "|">;
+  def XXORD  : ATOMIC_NOFETCH<BPF_DW, "u64", GPR, BPF_XOR, "^">;
+}
 
-  def XADDD  : ATOMIC_NOFETCH<BPF_ADD, "+">;
-  def XANDD  : ATOMIC_NOFETCH<BPF_AND, "&">;
-  def XORD   : ATOMIC_NOFETCH<BPF_OR, "|">;
-  def XXORD  : ATOMIC_NOFETCH<BPF_XOR, "^">;
+let Predicates = [BPFNoALU32] in {
+  def : Pat<(atomic_load_add_i32 ADDRri:$addr, GPR:$val),
+            (XADDW ADDRri:$addr, GPR:$val)>;
+  def : Pat<(atomic_load_add_i64 ADDRri:$addr, GPR:$val),
+            (XADDD ADDRri:$addr, GPR:$val)>;
 }
 
 // Atomic Fetch-and-<add, and, or, xor> operations
@@ -887,13 +862,6 @@ class XFALU32<BPFWidthModifer SizeOp, BPFArithOp Opc, string OpcodeStr,
   let BPFClass = BPF_STX;
 }
 
-let Constraints = "$dst = $val" in {
-  let Predicates = [BPFNoALU32] in {
-    def XADDW : XADD<BPF_W, "u32">;
-    def XFADDW : XFALU64<BPF_W, BPF_ADD, "u32", "add", atomic_load_add_i32>;
-  }
-}
-
 let Constraints = "$dst = $val" in {
   let Predicates = [BPFHasALU32], DecoderNamespace = "BPFALU32" in {
     def XFADDW32 : XFALU32<BPF_W, BPF_ADD, "u32", "add", atomic_load_add_i32>;
@@ -902,7 +870,9 @@ let Constraints = "$dst = $val" in {
     def XFXORW32 : XFALU32<BPF_W, BPF_XOR, "u32", "xor", atomic_load_xor_i32>;
   }
 
-  def XFADDD : XFALU64<BPF_DW, BPF_ADD, "u64", "add", atomic_load_add_i64>;
+  let Predicates = [BPFHasALU32] in {
+    def XFADDD : XFALU64<BPF_DW, BPF_ADD, "u64", "add", atomic_load_add_i64>;
+  }
   def XFANDD : XFALU64<BPF_DW, BPF_AND, "u64", "and", atomic_load_and_i64>;
   def XFORD  : XFALU64<BPF_DW, BPF_OR,  "u64", "or",  atomic_load_or_i64>;
   def XFXORD : XFALU64<BPF_DW, BPF_XOR, "u64", "xor", atomic_load_xor_i64>;
diff --git a/llvm/lib/Target/BPF/BPFMIChecking.cpp b/llvm/lib/Target/BPF/BPFMIChecking.cpp
@@ -0,0 +1,181 @@
+//===-------------- BPFMIChecking.cpp - MI Checking Legality -------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs checking to signal errors for certain illegal usages at
+// MachineInstruction layer. Specially, the result of XADD{32,64} insn should
+// not be used. The pass is done at the PreEmit pass right before the
+// machine code is emitted at which point the register liveness information
+// is still available.
+//
+//===----------------------------------------------------------------------===//
+
+#include "BPF.h"
+#include "BPFInstrInfo.h"
+#include "BPFTargetMachine.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "bpf-mi-checking"
+
+namespace {
+
+struct BPFMIPreEmitChecking : public MachineFunctionPass {
+
+  static char ID;
+  MachineFunction *MF;
+  const TargetRegisterInfo *TRI;
+
+  BPFMIPreEmitChecking() : MachineFunctionPass(ID) {
+    initializeBPFMIPreEmitCheckingPass(*PassRegistry::getPassRegistry());
+  }
+
+private:
+  // Initialize class variables.
+  void initialize(MachineFunction &MFParm);
+
+  void processAtomicInsts();
+
+public:
+  // Main entry point for this pass.
+  bool runOnMachineFunction(MachineFunction &MF) override {
+    if (!skipFunction(MF.getFunction())) {
+      initialize(MF);
+      processAtomicInsts();
+    }
+    return false;
+  }
+};
+
+// Initialize class variables.
+void BPFMIPreEmitChecking::initialize(MachineFunction &MFParm) {
+  MF = &MFParm;
+  TRI = MF->getSubtarget<BPFSubtarget>().getRegisterInfo();
+  LLVM_DEBUG(dbgs() << "*** BPF PreEmit checking pass ***\n\n");
+}
+
+// Make sure all Defs of XADD are dead, meaning any result of XADD insn is not
+// used.
+//
+// NOTE: BPF backend hasn't enabled sub-register liveness track, so when the
+// source and destination operands of XADD are GPR32, there is no sub-register
+// dead info. If we rely on the generic MachineInstr::allDefsAreDead, then we
+// will raise false alarm on GPR32 Def.
+//
+// To support GPR32 Def, ideally we could just enable sub-registr liveness track
+// on BPF backend, then allDefsAreDead could work on GPR32 Def. This requires
+// implementing TargetSubtargetInfo::enableSubRegLiveness on BPF.
+//
+// However, sub-register liveness tracking module inside LLVM is actually
+// designed for the situation where one register could be split into more than
+// one sub-registers for which case each sub-register could have their own
+// liveness and kill one of them doesn't kill others. So, tracking liveness for
+// each make sense.
+//
+// For BPF, each 64-bit register could only have one 32-bit sub-register. This
+// is exactly the case which LLVM think brings no benefits for doing
+// sub-register tracking, because the live range of sub-register must always
+// equal to its parent register, therefore liveness tracking is disabled even
+// the back-end has implemented enableSubRegLiveness. The detailed information
+// is at r232695:
+//
+//   Author: Matthias Braun <matze@braunis.de>
+//   Date:   Thu Mar 19 00:21:58 2015 +0000
+//   Do not track subregister liveness when it brings no benefits
+//
+// Hence, for BPF, we enhance MachineInstr::allDefsAreDead. Given the solo
+// sub-register always has the same liveness as its parent register, LLVM is
+// already attaching a implicit 64-bit register Def whenever the there is
+// a sub-register Def. The liveness of the implicit 64-bit Def is available.
+// For example, for "lock *(u32 *)(r0 + 4) += w9", the MachineOperand info could
+// be:
+//
+//   $w9 = XADDW32 killed $r0, 4, $w9(tied-def 0),
+//                        implicit killed $r9, implicit-def dead $r9
+//
+// Even though w9 is not marked as Dead, the parent register r9 is marked as
+// Dead correctly, and it is safe to use such information or our purpose.
+static bool hasLiveDefs(const MachineInstr &MI, const TargetRegisterInfo *TRI) {
+  const MCRegisterClass *GPR64RegClass =
+      &BPFMCRegisterClasses[BPF::GPRRegClassID];
+  std::vector<unsigned> GPR32LiveDefs;
+  std::vector<unsigned> GPR64DeadDefs;
+
+  for (const MachineOperand &MO : MI.operands()) {
+    bool RegIsGPR64;
+
+    if (!MO.isReg() || MO.isUse())
+      continue;
+
+    RegIsGPR64 = GPR64RegClass->contains(MO.getReg());
+    if (!MO.isDead()) {
+      // It is a GPR64 live Def, we are sure it is live. */
+      if (RegIsGPR64)
+        return true;
+      // It is a GPR32 live Def, we are unsure whether it is really dead due to
+      // no sub-register liveness tracking. Push it to vector for deferred
+      // check.
+      GPR32LiveDefs.push_back(MO.getReg());
+      continue;
+    }
+
+    // Record any GPR64 dead Def as some unmarked GPR32 could be alias of its
+    // low 32-bit.
+    if (RegIsGPR64)
+      GPR64DeadDefs.push_back(MO.getReg());
+  }
+
+  // No GPR32 live Def, safe to return false.
+  if (GPR32LiveDefs.empty())
+    return false;
+
+  // No GPR64 dead Def, so all those GPR32 live Def can't have alias, therefore
+  // must be truely live, safe to return true.
+  if (GPR64DeadDefs.empty())
+    return true;
+
+  // Otherwise, return true if any aliased SuperReg of GPR32 is not dead.
+  for (auto I : GPR32LiveDefs)
+    for (MCPhysReg SR : TRI->superregs(I))
+      if (!llvm::is_contained(GPR64DeadDefs, SR))
+        return true;
+
+  return false;
+}
+
+void BPFMIPreEmitChecking::processAtomicInsts() {
+  for (MachineBasicBlock &MBB : *MF) {
+    for (MachineInstr &MI : MBB) {
+      if (MI.getOpcode() != BPF::XADDW && MI.getOpcode() != BPF::XADDD)
+        continue;
+
+      LLVM_DEBUG(MI.dump());
+      if (hasLiveDefs(MI, TRI)) {
+        DebugLoc Empty;
+        const DebugLoc &DL = MI.getDebugLoc();
+        const Function &F = MF->getFunction();
+        F.getContext().diagnose(DiagnosticInfoUnsupported{
+            F, "Invalid usage of the XADD return value", DL});
+      }
+    }
+  }
+}
+
+} // namespace
+
+INITIALIZE_PASS(BPFMIPreEmitChecking, "bpf-mi-pemit-checking",
+                "BPF PreEmit Checking", false, false)
+
+char BPFMIPreEmitChecking::ID = 0;
+FunctionPass *llvm::createBPFMIPreEmitCheckingPass() {
+  return new BPFMIPreEmitChecking();
+}
diff --git a/llvm/lib/Target/BPF/BPFTargetMachine.cpp b/llvm/lib/Target/BPF/BPFTargetMachine.cpp
@@ -178,6 +178,7 @@ void BPFPassConfig::addMachineSSAOptimization() {
 }
 
 void BPFPassConfig::addPreEmitPass() {
+  addPass(createBPFMIPreEmitCheckingPass());
   if (getOptLevel() != CodeGenOptLevel::None)
     if (!DisableMIPeephole)
       addPass(createBPFMIPreEmitPeepholePass());
diff --git a/llvm/lib/Target/BPF/CMakeLists.txt b/llvm/lib/Target/BPF/CMakeLists.txt
@@ -39,6 +39,7 @@ add_llvm_target(BPFCodeGen
   BPFSubtarget.cpp
   BPFTargetMachine.cpp
   BPFMIPeephole.cpp
+  BPFMIChecking.cpp
   BPFMISimplifyPatchable.cpp
   BTFDebug.cpp
 
diff --git a/llvm/test/CodeGen/BPF/atomics.ll b/llvm/test/CodeGen/BPF/atomics.ll
@@ -1,19 +1,22 @@
-; RUN: llc < %s -march=bpfel -verify-machineinstrs -show-mc-encoding | FileCheck --check-prefixes=CHECK,CHECK-V2 %s
-; RUN: llc < %s -march=bpfel -verify-machineinstrs -show-mc-encoding -mcpu=v3 | FileCheck --check-prefixes=CHECK,CHECK-V3 %s
+; RUN: llc < %s -march=bpfel -verify-machineinstrs -show-mc-encoding | FileCheck %s
+; RUN: llc < %s -march=bpfel -verify-machineinstrs -show-mc-encoding -mcpu=v3 | FileCheck --check-prefix=CHECK-V3 %s
 
 ; CHECK-LABEL: test_load_add_32
-; CHECK-V2: r2 = atomic_fetch_add((u32 *)(r1 + 0), r2)
+; CHECK: lock *(u32 *)(r1 + 0) += r2
+; CHECK: encoding: [0xc3,0x21
 ; CHECK-V3: w2 = atomic_fetch_add((u32 *)(r1 + 0), w2)
-; CHECK: encoding: [0xc3,0x21,0x00,0x00,0x01,0x00,0x00,0x00]
+; CHECK-V3: encoding: [0xc3,0x21,0x00,0x00,0x01,0x00,0x00,0x00]
 define void @test_load_add_32(ptr %p, i32 zeroext %v) {
 entry:
   atomicrmw add ptr %p, i32 %v seq_cst
   ret void
 }
 
 ; CHECK-LABEL: test_load_add_64
-; CHECK: r2 = atomic_fetch_add((u64 *)(r1 + 0), r2)
-; CHECK: encoding: [0xdb,0x21,0x00,0x00,0x01,0x00,0x00,0x00]
+; CHECK: lock *(u64 *)(r1 + 0) += r2
+; CHECK: encoding: [0xdb,0x21
+; CHECK-V3: r2 = atomic_fetch_add((u64 *)(r1 + 0), r2)
+; CHECK-V3: encoding: [0xdb,0x21,0x00,0x00,0x01,0x00,0x00,0x00]
 define void @test_load_add_64(ptr %p, i64 zeroext %v) {
 entry:
   atomicrmw add ptr %p, i64 %v seq_cst
diff --git a/llvm/test/CodeGen/BPF/atomics_2.ll b/llvm/test/CodeGen/BPF/atomics_2.ll
@@ -224,7 +224,7 @@ entry:
 }
 
 ; CHECK-LABEL: test_atomic_xor_64
-; CHECK: r2 = atomic_fetch_xor((u64 *)(r1 + 0), r2)
+; CHECK: atomic_fetch_xor((u64 *)(r1 + 0), r2)
 ; CHECK: encoding: [0xdb,0x21,0x00,0x00,0xa1,0x00,0x00,0x00]
 ; CHECK: w0 = 0
 define dso_local i32 @test_atomic_xor_64(ptr nocapture %p, i64 %v) local_unnamed_addr {
diff --git a/llvm/test/CodeGen/BPF/objdump_atomics.ll b/llvm/test/CodeGen/BPF/objdump_atomics.ll
@@ -2,7 +2,7 @@
 
 ; CHECK-LABEL: test_load_add_32
 ; CHECK: c3 21
-; CHECK: w2 = atomic_fetch_add((u32 *)(r1 + 0), w2)
+; CHECK: lock *(u32 *)(r1 + 0) += w2
 define void @test_load_add_32(ptr %p, i32 zeroext %v) {
 entry:
   atomicrmw add ptr %p, i32 %v seq_cst
@@ -11,7 +11,7 @@ entry:
 
 ; CHECK-LABEL: test_load_add_64
 ; CHECK: db 21
-; CHECK: r2 = atomic_fetch_add((u64 *)(r1 + 0), r2)
+; CHECK: lock *(u64 *)(r1 + 0) += r2
 define void @test_load_add_64(ptr %p, i64 zeroext %v) {
 entry:
   atomicrmw add ptr %p, i64 %v seq_cst
diff --git a/llvm/test/CodeGen/BPF/xadd.ll b/llvm/test/CodeGen/BPF/xadd.ll
diff --git a/llvm/test/CodeGen/BPF/xadd_legal.ll b/llvm/test/CodeGen/BPF/xadd_legal.ll

Original file line number	Diff line number	Diff line change
`@@ -178,6 +178,7 @@ void BPFPassConfig::addMachineSSAOptimization() {`
`178`	`178`	`}`
`179`	`179`
`180`	`180`	`void BPFPassConfig::addPreEmitPass() {`
	`181`	`+ addPass(createBPFMIPreEmitCheckingPass());`
`181`	`182`	`if (getOptLevel() != CodeGenOptLevel::None)`
`182`	`183`	`if (!DisableMIPeephole)`
`183`	`184`	`addPass(createBPFMIPreEmitPeepholePass());`
Original file line number	Diff line number	Diff line change
`@@ -224,7 +224,7 @@ entry:`
`224`	`224`	`}`
`225`	`225`
`226`	`226`	`; CHECK-LABEL: test_atomic_xor_64`
`227`		`-; CHECK: r2 = atomic_fetch_xor((u64 *)(r1 + 0), r2)`
	`227`	`+; CHECK: atomic_fetch_xor((u64 *)(r1 + 0), r2)`
`228`	`228`	`; CHECK: encoding: [0xdb,0x21,0x00,0x00,0xa1,0x00,0x00,0x00]`
`229`	`229`	`; CHECK: w0 = 0`
`230`	`230`	`define dso_local i32 @test_atomic_xor_64(ptr nocapture %p, i64 %v) local_unnamed_addr {`