[WebAssembly] Restore __stack_pointer after catch instructions

Summary:
After the stack is unwound due to a thrown exception, the
`__stack_pointer` global can point to an invalid address. This inserts
instructions that restore `__stack_pointer` global.

Reviewers: jgravelle-google, dschuff

Subscribers: mgorny, sbc100, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D50980

llvm-svn: 340339

llvm/lib/Target/WebAssembly/CMakeLists.txt

@@ -20,6 +20,7 @@ add_llvm_target(WebAssemblyCodeGen
   WebAssemblyCFGStackify.cpp
   WebAssemblyCFGSort.cpp
   WebAssemblyLateEHPrepare.cpp
+  WebAssemblyEHRestoreStackPointer.cpp
   WebAssemblyExceptionInfo.cpp
   WebAssemblyExplicitLocals.cpp
   WebAssemblyFastISel.cpp

llvm/lib/Target/WebAssembly/WebAssembly.h

@@ -39,6 +39,7 @@ FunctionPass *createWebAssemblyArgumentMove();
 FunctionPass *createWebAssemblySetP2AlignOperands();
 
 // Late passes.
+FunctionPass *createWebAssemblyEHRestoreStackPointer();
 FunctionPass *createWebAssemblyReplacePhysRegs();
 FunctionPass *createWebAssemblyPrepareForLiveIntervals();
 FunctionPass *createWebAssemblyOptimizeLiveIntervals();
@@ -63,6 +64,7 @@ void initializeFixFunctionBitcastsPass(PassRegistry &);
 void initializeOptimizeReturnedPass(PassRegistry &);
 void initializeWebAssemblyArgumentMovePass(PassRegistry &);
 void initializeWebAssemblySetP2AlignOperandsPass(PassRegistry &);
+void initializeWebAssemblyEHRestoreStackPointerPass(PassRegistry &);
 void initializeWebAssemblyReplacePhysRegsPass(PassRegistry &);
 void initializeWebAssemblyPrepareForLiveIntervalsPass(PassRegistry &);
 void initializeWebAssemblyOptimizeLiveIntervalsPass(PassRegistry &);

llvm/lib/Target/WebAssembly/WebAssemblyEHRestoreStackPointer.cpp

@@ -0,0 +1,78 @@
+//===-- WebAssemblyEHRestoreStackPointer.cpp - __stack_pointer restoration ===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// After the stack is unwound due to a thrown exception, the __stack_pointer
+/// global can point to an invalid address. This inserts instructions that
+/// restore __stack_pointer global.
+///
+//===----------------------------------------------------------------------===//
+
+#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
+#include "WebAssembly.h"
+#include "WebAssemblySubtarget.h"
+#include "WebAssemblyUtilities.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/MC/MCAsmInfo.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "wasm-eh-restore-stack-pointer"
+
+namespace {
+class WebAssemblyEHRestoreStackPointer final : public MachineFunctionPass {
+public:
+  static char ID; // Pass identification, replacement for typeid
+  WebAssemblyEHRestoreStackPointer() : MachineFunctionPass(ID) {}
+
+  StringRef getPassName() const override {
+    return "WebAssembly Restore Stack Pointer for Exception Handling";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+};
+} // end anonymous namespace
+
+char WebAssemblyEHRestoreStackPointer::ID = 0;
+INITIALIZE_PASS(WebAssemblyEHRestoreStackPointer, DEBUG_TYPE,
+                "Restore Stack Pointer for Exception Handling", true, false)
+
+FunctionPass *llvm::createWebAssemblyEHRestoreStackPointer() {
+  return new WebAssemblyEHRestoreStackPointer();
+}
+
+bool WebAssemblyEHRestoreStackPointer::runOnMachineFunction(
+    MachineFunction &MF) {
+  const auto *FrameLowering = static_cast<const WebAssemblyFrameLowering *>(
+      MF.getSubtarget().getFrameLowering());
+  if (!FrameLowering->needsPrologForEH(MF))
+    return false;
+  bool Changed = false;
+
+  for (auto &MBB : MF) {
+    if (!MBB.isEHPad())
+      continue;
+    Changed = true;
+
+    // Insert __stack_pointer restoring instructions at the beginning of each EH
+    // pad, after the catch instruction. (Catch instructions may have been
+    // reordered, and catch_all instructions have not been inserted yet, but
+    // those cases are handled in LateEHPrepare).
+    auto InsertPos = MBB.begin();
+    if (WebAssembly::isCatch(*MBB.begin()))
+      InsertPos++;
+    FrameLowering->writeSPToGlobal(WebAssembly::SP32, MF, MBB, InsertPos,
+                                   MBB.begin()->getDebugLoc());
+  }
+  return Changed;
+}

llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp

@@ -30,6 +30,7 @@
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/MC/MCAsmInfo.h"
 #include "llvm/Support/Debug.h"
 using namespace llvm;
 
@@ -78,13 +79,23 @@ bool WebAssemblyFrameLowering::hasReservedCallFrame(
   return !MF.getFrameInfo().hasVarSizedObjects();
 }
 
+// In function with EH pads, we need to make a copy of the value of
+// __stack_pointer global in SP32 register, in order to use it when restoring
+// __stack_pointer after an exception is caught.
+bool WebAssemblyFrameLowering::needsPrologForEH(
+    const MachineFunction &MF) const {
+  auto EHType = MF.getTarget().getMCAsmInfo()->getExceptionHandlingType();
+  return EHType == ExceptionHandling::Wasm &&
+         MF.getFunction().hasPersonalityFn() && MF.getFrameInfo().hasCalls();
+}
 
 /// 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);
+  return MFI.getStackSize() || MFI.adjustsStack() || hasFP(MF) ||
+         needsPrologForEH(MF);
 }
 
 /// Returns true if the local user-space stack pointer needs to be written back
@@ -97,10 +108,9 @@ bool WebAssemblyFrameLowering::needsSPWriteback(
          MF.getFunction().hasFnAttribute(Attribute::NoRedZone);
 }
 
-static void writeSPToGlobal(unsigned SrcReg, MachineFunction &MF,
-                            MachineBasicBlock &MBB,
-                            MachineBasicBlock::iterator &InsertStore,
-                            const DebugLoc &DL) {
+void WebAssemblyFrameLowering::writeSPToGlobal(
+    unsigned SrcReg, MachineFunction &MF, MachineBasicBlock &MBB,
+    MachineBasicBlock::iterator &InsertStore, const DebugLoc &DL) const {
   const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
 
   const char *ES = "__stack_pointer";

llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.h

@@ -45,7 +45,15 @@ class WebAssemblyFrameLowering final : public TargetFrameLowering {
   bool hasFP(const MachineFunction &MF) const override;
   bool hasReservedCallFrame(const MachineFunction &MF) const override;
 
- private:
+  bool needsPrologForEH(const MachineFunction &MF) const;
+
+  /// Write SP back to __stack_pointer global.
+  void writeSPToGlobal(unsigned SrcReg, MachineFunction &MF,
+                       MachineBasicBlock &MBB,
+                       MachineBasicBlock::iterator &InsertStore,
+                       const DebugLoc &DL) const;
+
+private:
   bool hasBP(const MachineFunction &MF) const;
   bool needsSP(const MachineFunction &MF, const MachineFrameInfo &MFI) const;
   bool needsSPWriteback(const MachineFunction &MF,

llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

@@ -58,6 +58,7 @@ extern "C" void LLVMInitializeWebAssemblyTarget() {
   initializeOptimizeReturnedPass(PR);
   initializeWebAssemblyArgumentMovePass(PR);
   initializeWebAssemblySetP2AlignOperandsPass(PR);
+  initializeWebAssemblyEHRestoreStackPointerPass(PR);
   initializeWebAssemblyReplacePhysRegsPass(PR);
   initializeWebAssemblyPrepareForLiveIntervalsPass(PR);
   initializeWebAssemblyOptimizeLiveIntervalsPass(PR);
@@ -280,6 +281,9 @@ void WebAssemblyPassConfig::addPostRegAlloc() {
 void WebAssemblyPassConfig::addPreEmitPass() {
   TargetPassConfig::addPreEmitPass();
 
+  // Restore __stack_pointer global after an exception is thrown.
+  addPass(createWebAssemblyEHRestoreStackPointer());
+
   // Now that we have a prologue and epilogue and all frame indices are
   // rewritten, eliminate SP and FP. This allows them to be stackified,
   // colored, and numbered with the rest of the registers.

llvm/test/CodeGen/WebAssembly/exception.ll

@@ -19,9 +19,11 @@ define void @test_throw() {
 }
 
 ; CHECK-LABEL: test_catch_rethrow:
+; CHECK:   get_global  $push{{.+}}=, __stack_pointer@GLOBAL
 ; CHECK:   try
 ; CHECK:   call      foo@FUNCTION
 ; CHECK:   i32.catch     $push{{.+}}=, 0
+; CHECK:   set_global  __stack_pointer@GLOBAL
 ; CHECK-DAG:   i32.store  __wasm_lpad_context
 ; CHECK-DAG:   i32.store  __wasm_lpad_context+4
 ; CHECK:   i32.call  $push{{.+}}=, _Unwind_CallPersonality@FUNCTION
@@ -63,6 +65,7 @@ try.cont:                                         ; preds = %entry, %catch
 ; CHECK:   try
 ; CHECK:   call      foo@FUNCTION
 ; CHECK:   catch_all
+; CHECK:   set_global  __stack_pointer@GLOBAL
 ; CHECK:   i32.call  $push{{.+}}=, _ZN7CleanupD1Ev@FUNCTION
 ; CHECK:   rethrow
 ; CHECK:   end_try
@@ -161,10 +164,12 @@ terminate10:                                      ; preds = %ehcleanup7
 ; CHECK:  call      foo@FUNCTION
 ; CHECK:  i32.catch
 ; CHECK-NOT:  get_global  $push{{.+}}=, __stack_pointer@GLOBAL
+; CHECK:  set_global  __stack_pointer@GLOBAL
 ; CHECK:  try
 ; CHECK:  call      foo@FUNCTION
 ; CHECK:  catch_all
 ; CHECK-NOT:  get_global  $push{{.+}}=, __stack_pointer@GLOBAL
+; CHECK:  set_global  __stack_pointer@GLOBAL
 ; CHECK:  call      __cxa_end_catch@FUNCTION
 ; CHECK-NOT:  set_global  __stack_pointer@GLOBAL, $pop{{.+}}
 ; CHECK:  end_try