Imported Upstream version 5.18.0.205

Former-commit-id: 7f59f7e792705db773f1caecdaa823092f4e2927

external/llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp

@@ -0,0 +1,276 @@
+//===-- WebAssemblyFrameLowering.cpp - WebAssembly Frame Lowering ----------==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief This file contains the WebAssembly implementation of
+/// TargetFrameLowering class.
+///
+/// On WebAssembly, there aren't a lot of things to do here. There are no
+/// callee-saved registers to save, and no spill slots.
+///
+/// The stack grows downward.
+///
+//===----------------------------------------------------------------------===//
+
+#include "WebAssemblyFrameLowering.h"
+#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
+#include "WebAssemblyInstrInfo.h"
+#include "WebAssemblyMachineFunctionInfo.h"
+#include "WebAssemblySubtarget.h"
+#include "WebAssemblyTargetMachine.h"
+#include "WebAssemblyUtilities.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineModuleInfoImpls.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "wasm-frame-info"
+
+// TODO: wasm64
+// TODO: Emit TargetOpcode::CFI_INSTRUCTION instructions
+
+/// We need a base pointer in the case of having items on the stack that
+/// require stricter alignment than the stack pointer itself.  Because we need
+/// to shift the stack pointer by some unknown amount to force the alignment,
+/// we need to record the value of the stack pointer on entry to the function.
+bool WebAssemblyFrameLowering::hasBP(
+    const MachineFunction &MF) const {
+  const auto *RegInfo =
+      MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
+  return RegInfo->needsStackRealignment(MF);
+}
+
+/// Return true if the specified function should have a dedicated frame pointer
+/// register.
+bool WebAssemblyFrameLowering::hasFP(const MachineFunction &MF) const {
+  const MachineFrameInfo &MFI = MF.getFrameInfo();
+
+  // When we have var-sized objects, we move the stack pointer by an unknown
+  // amount, and need to emit a frame pointer to restore the stack to where we
+  // were on function entry.
+  // If we already need a base pointer, we use that to fix up the stack pointer.
+  // If there are no fixed-size objects, we would have no use of a frame
+  // pointer, and thus should not emit one.
+  bool HasFixedSizedObjects = MFI.getStackSize() > 0;
+  bool NeedsFixedReference = !hasBP(MF) || HasFixedSizedObjects;
+
+  return MFI.isFrameAddressTaken() ||
+         (MFI.hasVarSizedObjects() && NeedsFixedReference) ||
+         MFI.hasStackMap() || MFI.hasPatchPoint();
+}
+
+/// Under normal circumstances, when a frame pointer is not required, we reserve
+/// argument space for call sites in the function immediately on entry to the
+/// current function. This eliminates the need for add/sub sp brackets around
+/// call sites. Returns true if the call frame is included as part of the stack
+/// frame.
+bool WebAssemblyFrameLowering::hasReservedCallFrame(
+    const MachineFunction &MF) const {
+  return !MF.getFrameInfo().hasVarSizedObjects();
+}
+
+
+/// Returns true if this function needs a local user-space stack pointer.
+/// Unlike a machine stack pointer, the wasm user stack pointer is a global
+/// variable, so it is loaded into a register in the prolog.
+bool WebAssemblyFrameLowering::needsSP(const MachineFunction &MF,
+                                       const MachineFrameInfo &MFI) const {
+  return MFI.getStackSize() || MFI.adjustsStack() || hasFP(MF);
+}
+
+/// Returns true if the local user-space stack pointer needs to be written back
+/// to memory by this function (this is not meaningful if needsSP is false). If
+/// false, the stack red zone can be used and only a local SP is needed.
+bool WebAssemblyFrameLowering::needsSPWriteback(
+    const MachineFunction &MF, const MachineFrameInfo &MFI) const {
+  assert(needsSP(MF, MFI));
+  return MFI.getStackSize() > RedZoneSize || MFI.hasCalls() ||
+         MF.getFunction().hasFnAttribute(Attribute::NoRedZone);
+}
+
+static void writeSPToMemory(unsigned SrcReg, MachineFunction &MF,
+                            MachineBasicBlock &MBB,
+                            MachineBasicBlock::iterator &InsertAddr,
+                            MachineBasicBlock::iterator &InsertStore,
+                            const DebugLoc &DL) {
+  const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
+
+  const char *ES = "__stack_pointer";
+  auto *SPSymbol = MF.createExternalSymbolName(ES);
+  if (MF.getSubtarget<WebAssemblySubtarget>()
+        .getTargetTriple().isOSBinFormatELF()) {
+    MachineRegisterInfo &MRI = MF.getRegInfo();
+    const TargetRegisterClass *PtrRC =
+        MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
+    unsigned Zero = MRI.createVirtualRegister(PtrRC);
+
+    BuildMI(MBB, InsertAddr, DL, TII->get(WebAssembly::CONST_I32), Zero)
+        .addImm(0);
+    MachineMemOperand *MMO = MF.getMachineMemOperand(
+        MachinePointerInfo(MF.getPSVManager().getExternalSymbolCallEntry(ES)),
+        MachineMemOperand::MOStore, 4, 4);
+    BuildMI(MBB, InsertStore, DL, TII->get(WebAssembly::STORE_I32))
+        .addImm(2)  // p2align
+        .addExternalSymbol(SPSymbol)
+        .addReg(Zero)
+        .addReg(SrcReg)
+        .addMemOperand(MMO);
+  } else {
+    BuildMI(MBB, InsertStore, DL, TII->get(WebAssembly::SET_GLOBAL_I32))
+        .addExternalSymbol(SPSymbol)
+        .addReg(SrcReg);
+  }
+}
+
+MachineBasicBlock::iterator
+WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
+    MachineFunction &MF, MachineBasicBlock &MBB,
+    MachineBasicBlock::iterator I) const {
+  assert(!I->getOperand(0).getImm() && (hasFP(MF) || hasBP(MF)) &&
+         "Call frame pseudos should only be used for dynamic stack adjustment");
+  const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
+  if (I->getOpcode() == TII->getCallFrameDestroyOpcode() &&
+      needsSPWriteback(MF, MF.getFrameInfo())) {
+    DebugLoc DL = I->getDebugLoc();
+    writeSPToMemory(WebAssembly::SP32, MF, MBB, I, I, DL);
+  }
+  return MBB.erase(I);
+}
+
+void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
+                                            MachineBasicBlock &MBB) const {
+  // TODO: Do ".setMIFlag(MachineInstr::FrameSetup)" on emitted instructions
+  auto &MFI = MF.getFrameInfo();
+  assert(MFI.getCalleeSavedInfo().empty() &&
+         "WebAssembly should not have callee-saved registers");
+
+  if (!needsSP(MF, MFI)) return;
+  uint64_t StackSize = MFI.getStackSize();
+
+  const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
+  auto &MRI = MF.getRegInfo();
+
+  auto InsertPt = MBB.begin();
+  while (InsertPt != MBB.end() && WebAssembly::isArgument(*InsertPt))
+    ++InsertPt;
+  DebugLoc DL;
+
+  const TargetRegisterClass *PtrRC =
+      MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
+  unsigned SPReg = WebAssembly::SP32;
+  if (StackSize)
+    SPReg = MRI.createVirtualRegister(PtrRC);
+
+  const char *ES = "__stack_pointer";
+  auto *SPSymbol = MF.createExternalSymbolName(ES);
+  if (MF.getSubtarget<WebAssemblySubtarget>()
+        .getTargetTriple().isOSBinFormatELF()) {
+    unsigned Zero = MRI.createVirtualRegister(PtrRC);
+
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), Zero)
+        .addImm(0);
+    MachineMemOperand *LoadMMO = MF.getMachineMemOperand(
+        MachinePointerInfo(MF.getPSVManager().getExternalSymbolCallEntry(ES)),
+        MachineMemOperand::MOLoad, 4, 4);
+    // Load the SP value.
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::LOAD_I32), SPReg)
+        .addImm(2)       // p2align
+        .addExternalSymbol(SPSymbol)
+        .addReg(Zero)    // addr
+        .addMemOperand(LoadMMO);
+  } else {
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::GET_GLOBAL_I32), SPReg)
+        .addExternalSymbol(SPSymbol);
+  }
+
+  bool HasBP = hasBP(MF);
+  if (HasBP) {
+    auto FI = MF.getInfo<WebAssemblyFunctionInfo>();
+    unsigned BasePtr = MRI.createVirtualRegister(PtrRC);
+    FI->setBasePointerVreg(BasePtr);
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::COPY), BasePtr)
+        .addReg(SPReg);
+  }
+  if (StackSize) {
+    // Subtract the frame size
+    unsigned OffsetReg = MRI.createVirtualRegister(PtrRC);
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
+        .addImm(StackSize);
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::SUB_I32),
+            WebAssembly::SP32)
+        .addReg(SPReg)
+        .addReg(OffsetReg);
+  }
+  if (HasBP) {
+    unsigned BitmaskReg = MRI.createVirtualRegister(PtrRC);
+    unsigned Alignment = MFI.getMaxAlignment();
+    assert((1u << countTrailingZeros(Alignment)) == Alignment &&
+      "Alignment must be a power of 2");
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), BitmaskReg)
+        .addImm((int)~(Alignment - 1));
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::AND_I32),
+            WebAssembly::SP32)
+        .addReg(WebAssembly::SP32)
+        .addReg(BitmaskReg);
+  }
+  if (hasFP(MF)) {
+    // Unlike most conventional targets (where FP points to the saved FP),
+    // FP points to the bottom of the fixed-size locals, so we can use positive
+    // offsets in load/store instructions.
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::COPY),
+            WebAssembly::FP32)
+        .addReg(WebAssembly::SP32);
+  }
+  if (StackSize && needsSPWriteback(MF, MFI)) {
+    writeSPToMemory(WebAssembly::SP32, MF, MBB, InsertPt, InsertPt, DL);
+  }
+}
+
+void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
+                                            MachineBasicBlock &MBB) const {
+  auto &MFI = MF.getFrameInfo();
+  uint64_t StackSize = MFI.getStackSize();
+  if (!needsSP(MF, MFI) || !needsSPWriteback(MF, MFI)) return;
+  const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
+  auto &MRI = MF.getRegInfo();
+  auto InsertPt = MBB.getFirstTerminator();
+  DebugLoc DL;
+
+  if (InsertPt != MBB.end())
+    DL = InsertPt->getDebugLoc();
+
+  // Restore the stack pointer. If we had fixed-size locals, add the offset
+  // subtracted in the prolog.
+  unsigned SPReg = 0;
+  MachineBasicBlock::iterator InsertAddr = InsertPt;
+  if (hasBP(MF)) {
+    auto FI = MF.getInfo<WebAssemblyFunctionInfo>();
+    SPReg = FI->getBasePointerVreg();
+  } else if (StackSize) {
+    const TargetRegisterClass *PtrRC =
+        MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
+    unsigned OffsetReg = MRI.createVirtualRegister(PtrRC);
+    InsertAddr =
+        BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
+            .addImm(StackSize);
+    // In the epilog we don't need to write the result back to the SP32 physreg
+    // because it won't be used again. We can use a stackified register instead.
+    SPReg = MRI.createVirtualRegister(PtrRC);
+    BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::ADD_I32), SPReg)
+        .addReg(hasFP(MF) ? WebAssembly::FP32 : WebAssembly::SP32)
+        .addReg(OffsetReg);
+  } else {
+    SPReg = hasFP(MF) ? WebAssembly::FP32 : WebAssembly::SP32;
+  }
+
+  writeSPToMemory(SPReg, MF, MBB, InsertAddr, InsertPt, DL);
+}